The Geo-Social Model: A Transdisciplinary Approach to Flow-Type Landslide Analysis and Prevention

Abstract

Landslide disaster risks increase worldwide, particularly in urban areas. To design and implement more effective and democratic risk reduction programs, calls for transdisciplinary approaches have recently increased. However, little attention has been paid to the actual articulation of transdisciplinary methods and their associated challenges. To fill this gap, we draw on the case of the 1993 Quebrada de Macul disaster, Chile, to propose what we label as the Geo-Social Model. This experimental methodology aims at integrating recursive interactions between geological and social factors configuring landslide for more robust and inclusive analyses and interventions. It builds upon three analytical blocks or site-specific environments in constant co-determination: (1) The geology and geomorphology of the study area; (2) the built environment, encompassing infrastructural, urban, and planning conditions; and (3) the sociocultural environment, which includes community memory, risk perceptions, and territorial organizing. Our results are summarized in a geo-social map that systematizes the complex interactions between the three environments that facilitated the Quebrada de Macul flow-type landslide. While our results are specific to this event, we argue that the Geo-Social Model can be applied to other territories. In our conclusions, we suggest, first, that landslides in urban contexts are often the result of anthropogenic disruptions of natural balances and systems, often related to the lack of place-sensitive urban planning. Second, that transdisciplinary approaches are critical for sustaining robust and politically effective landslide risk prevention plans. Finally, that inter- and trans-disciplinary approaches to landslide risk prevention need to be integrated into municipal-level planning for a better understanding of—and prevention of—socio-natural hazards.

Full text

Sustainability 2021, 13, 2501. https://doi.org/10.3390/su13052501 www.mdpi.com/journal/sustainability
Article
The Geo-Social Model: A Transdisciplinary Approach
to Flow-Type Landslide Analysis and Prevention
Valentina Acuña 1,*, Francisca Roldán 2, Manuel Tironi 1 and Leila Juzam 1
1 Centro para la Gestión Integrada del Riesgo de Desastres (CIGIDEN), Pontificia Universidad Católica de
Chile, Santiago 8320000, Chile; metironi@uc.cl (M.T.); leila.juzam@cigiden.cl (L.J.)
2 Centro para la Gestión Integrada del Riesgo de Desastres (CIGIDEN), Universidad Católica del Norte,
Antofagasta 1240000, Chile; francisca.roldán@cigiden.cl
* Correspondence: vmacuna@uc.cl; Tel.: +56-982184518
Abstract: Landslide disaster risks increase worldwide, particularly in urban areas. To design and
implement more effective and democratic risk reduction programs, calls for transdisciplinary ap-
proaches have recently increased. However, little attention has been paid to the actual articulation
of transdisciplinary methods and their associated challenges. To fill this gap, we draw on the case
of the 1993 Quebrada de Macul disaster, Chile, to propose what we label as the Geo-Social Model.
This experimental methodology aims at integrating recursive interactions between geological and
social factors configuring landslide for more robust and inclusive analyses and interventions. It
builds upon three analytical blocks or site-specific environments in constant co-determination: (1)
The geology and geomorphology of the study area; (2) the built environment, encompassing infra-
structural, urban, and planning conditions; and (3) the sociocultural environment, which includes
community memory, risk perceptions, and territorial organizing. Our results are summarized in a
geo-social map that systematizes the complex interactions between the three environments that fa-
cilitated the Quebrada de Macul flow-type landslide. While our results are specific to this event, we
argue that the Geo-Social Model can be applied to other territories. In our conclusions, we suggest,
first, that landslides in urban contexts are often the result of anthropogenic disruptions of natural
balances and systems, often related to the lack of place-sensitive urban planning. Second, that trans-
disciplinary approaches are critical for sustaining robust and politically effective landslide risk pre-
vention plans. Finally, that inter- and trans-disciplinary approaches to landslide risk prevention
need to be integrated into municipal-level planning for a better understanding of—and prevention
of—socio-natural hazards.
Keywords: geo-social model; landslide; transdisciplinarity; community-based approach; integrated
research; human induced landslides; geo-social map
1. Introduction
Landslides (Landslides will be described according to the classification of Cruden,
D. & Varnes, D.J., 1996) will increase worldwide [1]. Due to growing urbanization, con-
tinuing deforestation and augmenting precipitations related to climatic pattern variability
are intensifying landslide events [2–4], affecting particularly socioeconomically vulnera-
ble exposed communities in urban areas [5–7]. In the case of Chile, mass flows constitute
one of the greatest geological threats in urban areas, with considerable human losses; this
has been explained in developing countries as a consequence of higher poverty rates,
more corrupt governments, and weaker healthcare systems [6,8]. In particular, the Met-
ropolitan Region—where Quebrada de Macul is located—is one of the areas with the
highest periodicity of landslide events in the last 30 years [9]. In fact, from 1908 to the
Citation: Acuña, V.; Roldán, F.; Ti-
roni, M.; Juzam, L. The Geo-Social
Model: A Transdisciplinary Ap-
proach to Flow-Type Landslide Anal-
ysis and Prevention. Sustainability
2021, 13, 2501. https://
doi.org/10.3390/su13052501
Academic Editor: Lucio Di Matteo
Received: 24 December 2020
Accepted: 13 February 2021
Published: 25 February 2021
Publisher’s Note: MDPI stays neu-
tral with regard to jurisdictional
claims in published maps and insti-
tutional affiliations.
Copyright: © 2021 by the authors. Li-
censee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and con-
ditions of the Creative Commons At-
tribution (CC BY) license (http://crea-
tivecommons.org/licenses/by/4.0/).

Sustainability 2021, 13, 2501 2 of 44
present there have been 12 alluvial events [9] including on of the worst national catastro-
phes since the 1950s: The flow of 3 May 1993 in Quebrada de Macul (henceforth QM).
That morning, intense rainfall, high temperatures, and a zero-degrees isotherm at
2000 m a.s.l. combined, generating the perfect conditions for debris flow and mudflow.
The result was a mass removal event of different pulses of debris and mud flow with
accumulated material of 6.5 × 105 and 1 × 106 m3, and with a deposit thickness reaching
more than 3 m in the axis of the stream composed of silt, sand, and blocks of up to 3 m in
diameter, in addition to eucalyptus trunks and anthropogenic debris. It should be noted
that the first flow began at 11:40 am with a debris flow of up to 1 m high, reaching speeds
of up to 15 km/h, and 30 km/h in the second pulse developed 10 min later, directly im-
pacting the urban area, destroying houses, trucks, sheds, trunks, etc. The consequence was
the devastation of urban areas along the ravine in the districts of La Florida and Peñalolén
in the metropolitan area of Santiago (Figure 1). The disaster left 26 deaths, 8 missing, 85
injured, and more than 30,000 people affected. In addition, 307 houses were destroyed
and another 5610 were severely damaged [10].
Figure 1. Macul basin (line in red) and the impact zone of the alluvial event of 3 May 1993 (area in light blue) in contrast
to the present urban area.
The memory of these events is still present in the community today, standing as a
major sociocultural marker in affected neighborhoods [10]. Since the catastrophe, the area
has undergone intense demographic transformations, including rapid urbanization and
gentrification processes [11]. This has not reduced, however, the likelihood of a similar
event today. Research has confirmed that anthropogenic modifications in the basin
mouth, particularly the loss of ground waterproofing due to piedmont urbanization, di-
rectly affect the quantity and speed of water flows as well as the hydraulic characteristics
of mountain sediments, configuring an important source of alluvial susceptibility [12].
Additionally, the expected effect of climate change on the hydrometeorology of the area
will likely mean a decrease in rainfall and flow levels, as well as an increase in annual

Sustainability 2021, 13, 2501 3 of 44
temperatures [13–16]. This could have important effects on the occurrence of floods and
flow-type landslides by contributing to the increase in the elevation of the 0 °C isotherm.
Furthermore, as an increase in the frequency and/or intensity of warm storms is expected,
these can produce runoff with high amounts of sediment in shorts periods of time.
The case of QM brings to the fore the complex interactions between hydrological,
geological, infrastructural, and sociocultural processes in landslide causes and effects,
particularly in the perspective of landslides prevention at the local level. It also points to
the lack of integrated, transdisciplinary analyses in Chile, Latin America, and developing
countries at large. Research to date has contributed to the characterization of the QM basin
and its geo- and hydromorphological features [6,9,17–21], of the history—and current pro-
cesses—of the area’s territorial planning [22], and the social imaginaries and organization
around the QM disaster [10,23]. These research agendas, however, have remained largely
unconnected, hence blocking the articulation of integrated models for participatory land-
slide risk management at the local level. In turn, this lack of integration has perpetuated
existent and obdurate disciplinary demarcations in landslide planning [24]. This is not
uncommon in the region. There is still limited understanding about the association be-
tween geological processes and the social, economic, and cultural factors driving flow-
type landslides [4]. This integration deficit is particularly acute in contexts of weak insti-
tutional structures, as in the case of Latin America, which hamper robust and effective
risk reduction initiatives [25,26].
This contrasts with the call made by the Agency for Integrated Risk Reduction Re-
search and Prevention [27–31]—a call reinforced by the Sendai Framework [32] and the
Global Assessment Report on Disaster Risk Reduction [33]. As it has been suggested by
these calls, a critical challenge is to provide practical solutions, education, communication,
and public outreach to reduce landslide disaster risk, to which end transdisciplinary in-
volvement, knowledge co-production, and process-oriented and territorially embedded
initiatives are fundamental components [24,33,34]. This implies, first and foremost, a sub-
stantive epistemological shift in the way that geohazards are understood, analyzed, and
intervened. As argued by Alcántara-Ayala [24] (p. 155), “most of the work on landslides
has been undertaken from a discipline-focused approach, especially in the physical, earth
sciences and engineering fields. To a lesser extent, investigations have been carried out
from a social science perspective, whereas Integrated Research on Landslide Disaster Risk
is practically non-existing”. This may be caused, as Matsura and Razak [35] (p. 5) suggest,
because “hazard science is still predominantly conducted in a traditional framework of
basic geosciences in which scientists do not feel the responsibility to translate knowledge
into actions”.
To fill this gap, in this paper we develop what we call the Geo-Social Model: a sys-
tematic attempt at integrating diverse knowledges for assessing and acting upon complex
geoclimatic events. The Geo-Social Model aims at integrating geological and social anal-
yses for flow-type landslide reduction and planning, while also incorporating local com-
munities as fundamental scientific and political actors. Drawing on the case of QM, the
Geo-Social Model therefore is, we suggest, a research device, a policy tool, and an episte-
mological proposition.
The reminder of the paper is organized as follows. We first describe our analytical
framework and methodological approach to the QM case. Second, we apply the Geo-So-
cial Model through a transdisciplinary approach. Third, we identify the interactions be-
tween geological, planning, and social processes and visualize them via a geo-social map.
Finally, we discuss our results with the broader literature. While we apply the model to
the QM case, we suggest that the Geo-Social Model—by identifying and analyzing the
connections of the above-mentioned processes—offers a robust tool to (a) understand the
complex phenomenology of the landslides than impact in urban zones, (b) integrate the
community in disaster risk reduction initiatives, and (c) connect scientific research to pol-
icy making in diverse contexts.

Sustainability 2021, 13, 2501 4 of 44
2. Materials and Methods
2.1. Analytical Framework
The analytical framework of this study is based on the category of geo-social pro-
cesses, highlighting the role of transdisciplinarity as both a conceptual and methodologi-
cal tool for landslide analysis and prevention.
2.1.1. The Geo-Social Model
In this paper, we attempt at integrating recursive interactions between geological and
social factors configuring and understanding landslides-related certain characteristics.
These interactions have been described independently, focusing on geology → social in-
teractions or on social → geology interactions [36,37], seldom recognizing co-determina-
tions (geology ←→ social interactions We borrow from Clark and Yusoff [38] and their
understanding of “geosocial formations” as processes in which geological events are in-
fluenced by social trajectories, just as much as social phenomena are shaped by geological
conditions. This approach builds on current theorizations that have recognized the mat-
tered condition of human and social life [39] and the urgent need to include more-than-
biological elements in the explanation of social processes [40,41]. This perspective is also
consistent with the ecosystem-based disaster risk reduction model [42] in as much as it
also attempts at linking physical exposure to infrastructure and socio-economic resilience.
Our model, however, emphasizes the relevance of geophysical conditions in the under-
standing of landslide-related hazards.
To operationalize our Geo-Social Model, we identify three analytical blocks or site-
specific environments in constant interaction: (1) The geological environment or the char-
acterization of the basin, which includes the geology and geomorphology; (2) the built
environment, encompassing infrastructural, urban, and planning conditions; and (3) the
sociocultural environment, which includes community memories, individual and collective
risk perceptions, and local organizations.
2.1.2. Transdisciplinary Approach
We define transdisciplinary research as iterative methods seeking the involvement
of actors from outside academia into the research process in order to integrate the best
available knowledge, reconcile values and preferences, as well as create ownership for
problems and solution options [43]. Transdisciplinary research, in the context of landslide
risk reduction, aims at combining different scientific disciplinary approaches with tradi-
tional, indigenous, and community knowledge to solve problems associated with local
risk reduction programs that account for diverse spatial-temporal scales under no episte-
mological and methodological constraints, entitling decision and policymaking for socie-
tal benefit and territorial sustainability [24,44].
The Geo-Social Model takes an explicit transdisciplinary perspective (Figure 2). By
embracing a holistic approach, the model assumes, in ontological terms, that environmen-
tal, social, and built systems are inextricably coupled. Epistemologically, it assumes that
co-produced and collaborative knowledge allows for mutual learning, better account of
uncertainties, and better policy decisions [45].

Sustainability 2021, 13, 2501 5 of 44
Figure 2. Location map of the Macul basin. (A) Chile location map on a national scale. (B) Location of the Metropolitan
Region of Santiago, Chile. (C) Location of the study area that includes the perimeter of the municipalities of the Metropol-
itan Region.

Sustainability 2021, 13, 2501 6 of 44
2.2. Research Site: The Macul Basin
Macul basin (QM) is located in the central zone of Chile, in the city of Santiago of the
Metropolitan Region; specifically, in the municipalities of La Florida and Peñalolén, in the
western zone of the Andes Mountains and the Central Depression (between the coordi-
nates 6,288,809–6,294,807 mN and 353,855–366,536 mE, respectively). Both represent cases
of population and urban growth (La Florida is the fourth district with the largest popula-
tion in the metropolitan region according to the 2017 CENSUS with 366,916 inhabitants
while Peñalolén occupies the 13th position with 241,599 inhabitants [46]). The urban ex-
pansion percentage towards the piedmont for the period 1995–2016 was 7.1 in La Florida
and 14.1 in Peñalolén [47] towards peripheral areas with a large presence in the piedmont
area with a spatial reconfiguration given by gentrification processes [48] (Figure 3).
Figure 3. Geo-Social Model diagram. Source: Authors’ own elaboration.
2.3. Methodology
We simultaneously applied disciplinary specific methods (Table 1), in-situ iterative
and participatory mixed methodology in order to share findings, identify interactions,
and find spaces of collaboration and co-construction of knowledge. For the last, we trian-
gulated evidence from the three environments. In general terms, triangulation refers to
the process by which multiple research strategies are brought together [49]. In this case,
we carried out holistic triangulation for capturing “more complete, holistic, and contex-
tual portrayal of the unit(s) under study” and enriching “our understanding by allowing
for new or deeper dimensions to emerge” [50] (pp. 603–604). We did this through period-
ical meetings between the research team where evidence from each environment was

Sustainability 2021, 13, 2501 7 of 44
shared and discussed. In order to establish transdisciplinary conceptual connections, vis-
ual aids were done through the use of diagrams and the elaboration of a geo-social map
with the ArcGIS—Arc.Map 10.8, Arcgis Pro 2.6 and Illustrator v24.1 software, which syn-
thesizes the interconnections between the results of the three environments of our Geo-
Social Model.
Table 1. Methodological synthesis.
Geological Environment Built Environment Socio-Cultural Environment
Meth-
ods
Generation of maps and geologi-
cal and geomorphological analy-
sis using quantitative and quali-
tative methodologies.
Qualitative case study approach:
archival research.
Qualitative case study ap-
proach: in-depth interviews,
ethnographic observations, and
participatory methods.
Materi-
als
Bibliographic references, digital
elevation model, satellite images
and historical geographic maps.
Chilean Daily Documentary Fund
(BN), digital map library (BN and
UCH) and administrative docu-
ments, mass media.
Oral testimonies, interviews,
observations, and photographs.
Data
Collec-
tion
Transfer, purchase, search infor-
mation and images.
Transfer and paleography of ar-
chival and audiovisual materials.
Participatory observation, in-
terviews, photographic record.
Data
analysis
Digitization of geographic infor-
mation, digital elevation model
processing and photointerpreta-
tion.
Hermeneutic and three level lec-
ture.
Contextual data analysis and
three level lecture.
In situ iterative and participatory mixed methodology
Periodic meetings, evidence shared and co-construction of knowledge.
For the geological environment, a geological characterization is developed, geomor-
phological landforms, in addition to a morphometric analysis representing the quantita-
tive analysis of the geographical surface [51], with the aim of deepening its characteriza-
tion and obtaining information on the hydrological response of the basin. All this because
these factors are considered, among the most relevant in the development of flow-type
landslides [52–55], which in turn are influenced by each other in different ways and de-
grees.
Specifically, the morphometric analysis is carried out by analyzing the basin (the
mouth area is not considered since the contribution area is analyzed, which in this case is
represented by the Macul basin) based on its physical parameters and its shape, from the
calculation and classification of numerical values based on the work of different authors
[56], in which case they include different parameters: Shape parameters, drainage net-
work, relief, and complementary parameters. The choice of each of these parameters and
the corresponding analysis is due to the type of information they provide and their use-
fulness for this particular area. For this purpose, Digital Elevation Model (DEM) pro-
cessing was carried out using specific geoprocessing tools of ArcGis Pro v26.0.0 and
ArcMap v10.8 software. The first and fundamental step is the delimitation of the area and
perimeter of the Macul basin (QM), in addition to generating the drainage network of the
basin with the use of Arc Hydro Tools and Hydrology of Spatial Analyst tools, whose
processing is summarized in Table 2.

Sustainability 2021, 13, 2501 8 of 44
Table 2. Geoprocessing of Digital Elevation Models (DEM) in ArcGis Pro v26.0.0 and ArcMap v10.8 software to obtain
relief and drainage parameters such as the area and perimeter of the Macul basin, as well as the drainage network.
Arc Hidro Tools—Spa-
tian Analyst Tool Basin Drainage Use
Fill Sink x x Digital correction of errors due to image resolution, obtaining more
accurate elevations and depressions. RASTER format.
Flow direction x x Characterization of the flow direction. RASTER format
Flow Accumulation x x Determines in which specific area there is a considerable flow accu-
mulation. RASTER format.
Stream Definition x
Definition of drainage density. RASTER format
Con—mathematical
conditional x
Stream Segmentation x
Distinguish each section of the stream based on its junctions. RAS-
TER format.
Stream Link
x
Stream Order x
Assign a numerical order to the segments of a RASTER representing
the drainage networks using Strahler’s methodology. RASTER for-
mat.
Catchment grid deline-
ation x Delineation of the sub-basins in question by cells. RASTER format.
Catchment polygon
processing x Transformation of RASTER format into VECTORIAL format.
Stream to Feature
x
Atribute Table—Calcu-
late Geometry x x Calculations tool on all or selected records for calculate area, length,
perimeter, and other.
Once these data were obtained, we proceeded to establish the methodology for ob-
taining each of the morphometric parameters mentioned above (Table 3), to subsequently
obtain the results using mathematical calculation tools of ArcGis Pro v26.0.0 and ArcMap
v10.8 software, and complementarity by exporting the resulting data in spreadsheets in
Microsoft Excel software. It should be noted that the hypsometric curve was obtained by
calculating ranges of height classes every 100 m, in order to subsequently calculate the
Relative Elevation and Relative Area of the basin. All this by means of geoprocessing
Mask, Reclass, dissolve of ArcGis Pro v26.0.0 with the use of DSM of 4.3 m and export of
data from the table of attributes to Excel spreadsheets to later generate the corresponding
graph.

Sustainability 2021, 13, 2501 9 of 44
Table 3. Definition and methodology for obtaining morphometric parameters of the Macul basin.
Form Parameters
Name Equation or Method Description
Basin Area (A) [km
2
]
Geographic information system (GIS)
A measure of the surface area of a surface of a basin, defined as the orthogonal projection of the entire
drainage area of a runoff system directed directly or indirectly to the same natural channel (López,
2008).
Basin Perimeter (P) [km] It is defined as the measurement of the watershed envelope line, by the topographic watershed (Gaspari,
2012).
Axial Length (A
l
) [km] Distance in a straight line between the mouth and the farthest point on the perimeter (P) of the basin,
which in some cases coincides with the length of the main course (Gaspari, 2012)
Length of the main channel (Lc)
[km]
Represents the length of the channel over its entire length (km), including all the sinuosity of the chan-
nel.
Form Factor (F) (Horton, 1932)
It is defined as the ratio between the area (A) and the length of the drainage basin (L
c
).
Compactness Factor (K
c
) (Grave-
lius, 1914)
This factor is the oldest one, expresses the relationship between the perimeter of the drainage basin and
that of a circle of equal area (equivalent circle); thus, the higher the coefficient, the more distant the
shape of the basin will be with respect to the circle. P represents the perimeter (km) and A the area (km
2
)
of the Macul basin.
Drainage System Parameters
Name Equation or Method Description
Drainage order (n) (Strahler, 1964) Geographic information system (GIS)
Horton (1945) suggests a hierarchization of streams according to order number as a measure of the
branching of the main channel in a basin. This system is dimensionless and was later improved and
slightly modified by Strahler (1964), indicating that a stream may have one or more segments.
Bifurcation ratio (B
r
) (Strahler,
1964)
It is the ratio between the total number of drains of a certain order (n
i
) and the total number of drains of
the next higher order (n
i+1
).
Length Ratio (L
r
) (Strahler, 1964) The ratio of the average length of a certain order of drainage to the average length (L
i
) of the drainages
of immediately lower order (L
i-1
).
Density of the drainage network
(Dd) (Horton, 1945) [1/km]
Quotient between the total length of the channels of all the orders that make up the river system of the
basin (∑L
i
) and the total area of the basin (A).
F=
 (2)
()
2
()
= 0.28  (  ()
 (2))
= 
 +1
=  ()
 −1()
 =  ()
 (2)

Sustainability 2021, 13, 2501 10 of 44
Drainage Frequency (F) (Ordoñez,
2011 in Garay & Agüero, 2018)
[1/km
2
].
It is defined as the quotient between the total number of river courses (n
t
) and the area of the basin
(km
2
). When obtained, it establishes the greater or lesser possibility that any drop of water will find a
channel in a greater or lesser time.
Drainage hierarchy (J) Geographic information system (GIS) Represents the highest drainage order, obtained using Strahler’s (1964) drainage order methodology.
Relief Parameters
Name Equation or Method Description
Absolute elevation difference (H)
[m a.s.l.]
Corresponds to the difference between the maximum elevation (HM) and the minimum elevation (Hm),
measured in meters above sea level (m a.s.l.).
Average slope of the basin (Sm)
[%] Geographic information system (GIS) The average slope of a watershed is directly related to the degradation process to which a watershed is
subjected (López Cadenas de Llano, 1998).
Hypsometric curve (Strahler, 1964)
Geographic information system (GIS) and
mathematical calculations by calculating rel-
ative elevation and relative area, and then
applying the results to a graph
The hypsometric curve suggested by Langbein et al. (1947) graphically represents the elevations of the
terrain as a function of the corresponding surfaces. According to Strahler (1964), the importance of this
relationship lies in the fact that it is an indicator of the state of dynamic equilibrium of the basin, so the
basin can be in a state of youth (disequilibrium), in a state of old age (equilibrium) or at intermediate
levels.
Complementary Parameters
Name Equation or Method Description
Torrentiality coefficient (T
c
) (López
and Romero, 1987) (1/km
2
)
Index that measures the degree of torrentiality of the basin, by means of the ratio of the number of
drainages of order 1 (n
1
) with respect to the total area of the basin (A).
Basin Efficiency Index (I
e
) (Ara-
cena, 1993)
Relationship between drainage density (Dd), watershed drainage hierarchy (J), watershed area (A) and
average slope (Sm). This value relates the characteristics of the basin in terms of efficiency or productiv-
ity for the triggering of debris flow or alluvium processes.
Potentiality index (P
i
) (Börgel,
1978)
It determines the location of erosion and accumulation zones in a watershed; its determination is im-
portant. A high P
I
value will reveal that in a specific hydrological basin there is accumulation of debris,
which could be transported if high precipitation occurs, as to generate an alluvial event (Arcadis, 2008).
Storage Coefficient (S
c
) (Garay &
Agüero, 2018)
It allows evaluating the storage capacity of the basin during rainfall floods, through the relationship be-
tween the Logitude Ratio (R
l
) and the Bifurcation Ratio (R
b
). If the storage coefficient is high, there is a
lower drainage density, which implies a lower amount of water effectively available to runoff on the
surface, as a result of infiltration.
 = 
 (2)
 ( . . )=( − )
( . . . )
= 1
 (2)
= 1
0.3+(0.3)+
( (2)0.3)+ ( (%)0.1)
= ( 1
+  1
2+)
 (2)
 = 


Sustainability 2021, 13, 2501 11 of 44
In addition, a geomorphological landform map was made using a mainly qualitative
methodology (with the exception of the delimitation of slopes and escarpments, which
were identified from slope map from DEM and DSM) with the adaptation and modifica-
tion to this particular geographic area of the methodology applied by the Colombian Ge-
ological Service or SGC [57], since its objective is the zoning of susceptibility and threat
due to landforms, in addition to having a wide and successful experience in research and
application in urban areas. Landforms are considered as a land surface that reflects a typ-
ical configuration of each environment, defined in its development by a particular process
with morphological characteristics, as well as some intrinsic properties (lithology, fractur-
ing, weathering, among others), which are combined in a physical space and determine
the generation of a mass movement [57]. This was done through a bibliographic study,
identification, and mapping of existing landforms. Specifically, DEM and DSM (Table 4)
were used to delimit slopes and escarpments, as well as to identify riverbeds and to un-
derstand the morphology of the basin relief. In addition, the geological cartography gen-
erated was used, as well as photointerpretation at scales ranging from 1:1:1000 to 1:20,000
with the use of high-resolution satellite images. In its development, substantial surface
changes were identified in the mouth area, due to anthropogenic influence, and therefore,
multitemporal mapping is incorporated through Google Earth Pro v7.3.3.7786 images (Ta-
ble 4) and the use of historical maps for landform delimitation of urban areas and agricul-
tural and land leveling surfaces on alluvial fans, identifying their evolution over time and
advancing in the understanding of how they influence in triggering socio-natural disas-
ters.
Table 4. Description of the basic inputs used for the development of the analysis and characterization of the geological
environment.
N° Image Year Resolution DATUM Satellite (s) Utilization
1 Base Map (satelital) 2017—
2019
0.31 m × 0.31 m
0.46 m × 0.46 m
0.5 m × 0.5 m
WGS-1984
Esri. Maxar. GeoEye. Earth-
star Geographics.
CNES/Airbus DS. USDA.
USGS. AeroGRID. IGN.
and the GIS User Commu-
nity
Mapping
base
2 Image 1993 - Georeferencing
WGS-1984 Google Earth Pro
3 Historical map 1861 - Georeferencing
WGS-1984 -
4 Digital Surface Model
(DSM) - 4.3 m × 4.3 m WGS-1984
Acquired by the Research
Center for Integrated Disas-
ter Risk Management
(CIGIDEN) Morphomet-
ric and mor-
phological
analysis
5 Digital Elevation
Model (DEM) - 12.5 m × 12.5 m WGS-1984 National Aeronautics and
Space Administration
(NASA)
6 Digital Elevation
Model SRTM (DEM) - 30 m × 30 m WGS-1984
On the other hand, the geological characterization allows determining the type of
deposit present in the basin, which conditions certain characteristics in its hydrological
behavior, considering that deposits with high permeability tend to be mobilized by easy
infiltration, these being generally of alluvial, colluvial, and volcanoclastic deposits, among
others [58]. For this, an identification, mapping, and description of the consolidated and
unconsolidated geological units of the Macul basin (QM) was carried out by collecting,
digitizing, and using bibliographic information [6,9,21,59,60] in conjunction with photoin-
terpretation of the units that make up the study area based on a multiscale methodology

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from 1:1000 to 1:20,000 with the use of high-resolution satellite images (Table 4) with the
use of ArcGis Pro v26.0.0 software. Emphasis was given to unconsolidated geological
units, such as alluvial and colluvial deposits, among others, due to their preponderance
to be transported by flow-type landslides. Finally, the deposit area of the mouth zone cor-
responding to the alluvial event of 1993 was digitally zoned by georeferencing impact
maps from official geological reports of the National Service of Geology and Mining [54]
(SERNAGEOMIN—Naranjo & Varela, 1993), which contain empirical field data and rep-
resent accurate data of the most important alluvial event recorded in that area.
To account for the built and socio-cultural environment, we applied a qualitative case
study approach. This method allowed an in-depth and empirical examination of the allu-
vial phenomenon in the context of the community’s daily lives and memories. Specifically,
the case study approach responds to a delimited case in which there is little clarity of the
relationships between a specific phenomenon and its context [61] and involves the explo-
ration of it over time through the collection of detailed data and the use of multiple sources
of information [62,63].
For the built environment we used archival research, which consists in the analysis
of historical documentation from public and private archives. Data collection was done
through reviews and transcriptions of written press from the Chilean Daily Documentary
Fund of the National Library of Chile, its digital map library, and the map library of the
School of Architecture and Urban Planning at Universidad de Chile, a palaeography of
colonial maps was done. Administrative documents from the Ministry of Public Works,
Directorate of Hydraulic Works, and the corresponding municipalities were also com-
piled and analyzed. Finally, documents and photographs from personal archives of sur-
vivors were digitized, together with the audiovisual and written material from mass me-
dia social networks that recorded the 1993 event and its subsequent commemorations.
Data analysis was carried out applying a hermeneutic and three-level lecture.
For the socio-cultural environment we followed the same method via in-depth inter-
views, ethnographic observations, and participatory methods. Data collection was exten-
sive [62] using participatory observation techniques, interviews, and photographical reg-
ister. The participatory methodology consisted of the research team’s engagement in ac-
tivities carried out by local organizations and field visits made between July 2019 and
March 2020; both were accompanied by photographic records and observation notes [64].
In-depth interviews were conducted through a selective sampling of key actors who sur-
vived the alluvium (N = 10), applying a standard semi-structured interview and contex-
tual (non-cross-sectional) data analyses at three levels: Literal, interpretative, and reflec-
tive [65] following a general inductive approach that considered the emergence of con-
ceptual categories and themes from the data.
3. Results
The results given by the Geo-Social Model are synthesized in the following diagram
(Figure 4) showing the principal characteristics of each environment. To account for them
we first describe and analyze the evidence of each. Secondly, we make their interconnec-
tions visible through a geo-social map.

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Figure 4. Results synthesis diagram.
3.1. Geological Environment
Characterization of the Macul Basin (QM)—Geology and Geomorphology
Based on historical alluvial events, it has been determined in the case of Santiago that,
when flows develop, they usually directly impact the urban areas of the mountain foot-
hills. However, the origin of these alluvial phenomena is not located in these particular
areas; on the contrary, they originate in the so-called basins (water basins) located in this
case in the western zone of the Andes, whose type of flow will depend on certain condi-
tioning factors such as geological and geomorphological factors, among others. That is
why a characterization of the basin allows progress in the understanding of these phe-
nomena, and in turn, allows providing relevant information to the population and public
entities.
The geomorphological characterization using landforms resulted in the identification
and zoning of 18 types, representing denudational, structural, fluvial, and alluvial geo-
morphological environments and anthropogenic environments (Table 5). These land-
forms represent surface forms with their own distinctive characteristics of the basin,
among them the Sos structural mountain range, which is characterized by the great struc-
tural influence of the Andes mountain range translated into topographic prominences of
mountainous and elongated morphology with steep to abrupt slopes (Sesso and Seslso),
which provide direct runoff in addition to high flow velocities and possibly dragging of
material. In addition, Sos includes a significant number of landforms with denudational
and fluvial and alluvial environments (Dlcdra, Dus, Dflc, Duf, Fffp, Frt and Fac), which
are prone to be affected and contribute to debris flow towards low slope areas, which are
characterized by an important anthropogenic influence, represented in this case by the

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settlement of urban constructions on the alluvial fans of the mouth area (Au-Faf). This is
quite relevant, taking into consideration that the alluvial fans (Faf) indicate historical
and/or recent discharges of alluvial material, therefore they are indicators of areas of sus-
ceptibility to the impact of this type of phenomena; however, it is highly populated. The
results of multitemporal landform analysis (Figures 5 and 6), allowed us to identify its
evolution in terms of influence and modification of the surface of this particular area, re-
sulting in an initial tendency from 1881 to settlement in areas relatively far from the apex
of the outfall area, even with a low percentage of Au areal. This is quite different from the
current scenario, which resulted in a strong tendency to an increase of Au and Aatg settled
in Faff, towards areas increasingly closer to the Macul basin (apex of the mouth area),
some of them even being located near Aac (Figure 6), this being coherent based on records
of urban expansion in the foothills of the Cordillera (Section 3.3.2).
Figure 5. Trend of areal variation of landform with multitemporal area at the mouth of the Macul basin.

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Table 5. Result of the geomorphological analysis through the identification and characterization of landforms. The results of these are stipulated, in addition to the establishment of the
definition and characteristics of each one of them.
N°
Geomorpho-
logical Envi-
ronment
Name of Landform Code Description
1
Denudational
Environment
Escarpments or slide
slopes Dess Surfaces or planes of variable dimensions, usually very steep and with undulating morphology, which have
been exposed due to landslides of rocks or rotational or translational soils (adapted from SGC, 2012)
2 Lobe or cone of debris or
rock avalanches Dlcdra
Lobe or fan-shaped structure with a long, convex length and steep natural slopes. Its origin is related to non-
channeled avalanches induced by gravitational processes, which may be intensified by seismic events or heavy
rains (adapted from SGC, 2012).
3 Undifferentiated slide
lobe or cone Dus
Cone or lobe-shaped structure with a low and gently undulating morphology. Its origin is related to the accu-
mulation of materials of very diverse origin and granulometry, as well as to mass movements with the capacity
to remove very heterogeneous materials, which slide along a relatively planar or furrow-shaped fault surface.
4 Flow lobe or cone Dflc
Lobe- or fan-shaped structure with a terraced or locally terraced, hilly morphology, with very variable lengths
ranging from short to extremely long. Its origin is related to channeled fluvio-torrential events or to the
transport of materials resulting from soil saturation. Its deposit could be constituted by angular to subrounded
blocks embedded in a fine or medium-sized matrix (adapted from SGC, 2012).
5 Undifferentiated flow
lobe or cone Duf
A lobe or fan-shaped structure with a convex, convex, lobed morphology, with a very long and abrupt length.
Its origin is related to torrential avalanches possibly induced by seismic events or torrential rains capable of re-
moving very heterogeneous materials. Its deposit could be constituted by angular to subrounded rocky blocks
of diverse origin and granulometry embedded in a clayey sandy matrix and by the accumulation of blocks at
the wave front
(adapted from SGC, 2012).
6 Fluvial and
alluvial envi-
ronment
Alluvial or fluvial fan Faf
Cone-shaped surface, with concave to convex slopes of flat, terraced morphology. Its origin is related to radial
torrential and fluvial accumulation, where a stream flows into a flat area. The alluvial deposits are deposited
radially from the apex of the fan located at the outlet of the stream from the mountains. The channels flow cut-
ting the fan, being deeper at the fan apex and shallower as they move away from it (adapted from SGC, 2012).
7 Alluvial or fluvial fan of
1993
Faf
1993
Lobe-shaped surface, with a flat, terraced morphology. Its origin is related to the alluvial torrential accumula-
tion in the alluvial event of 1993, in a radial form, where a stream flows into a flat area corresponding to urban-
ized zones (adapted from SGC, 2012).

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8 Alluvial or fluvial chan-
nel Fac
Irregularly shaped channel excavated by erosion of perennial or seasonal streams, within rock massifs and allu-
vial or fluvial sediments. Depending on the amount of sediment load, slope and flow, they can form varied sys-
tems (adapted from SGC, 2012).
9 Flat or flood plain Fffp
Flat, low to undulating morphology surface, eventually floodable. It is located bordering alluvial river chan-
nels. It includes the minor fluvial planes in “V” shapes, where the fluvial currents tend to join with their tribu-
taries to form the main channel. Its deposits may be constituted by fine sediments, originated during fluvial
flooding events (adapted from SGC, 2012).
10 River terraces Frt
Superficies elongadas, planas a suavemente onduladas, modeladas sobre sedimentos fluviales, limitadas por
escarpes de diferente altura a lo largo del cauce de un arroyo. Su origen se relaciona a procesos de erosión y
acumulación fluvial dentro de antiguas llanuras de inundación. Sus depósitos podrían estar constituidos por
gravas, limos y arcillas, con disminución del tamaño a medida que se alejan del cauce del río (adapted from
SGC, 2012).
11
Structural en-
vironment
Erosive scarps of struc-
tural origin Sesso
Elongated, flat to gently undulating surfaces, modeled on fluvial sediments, bounded by escarpments of differ-
ent heights along a stream channel. Their origin is related to fluvial erosion and accumulation processes within
ancient flood plains. Their deposits could be made up of gravels, silts and clays, decreasing in size as they move
away from the riverbed (>55°) (adapted from SGC, 2012 and Sánchez, 2014).
12 Erosive slopes of struc-
tural origin Seslso
Sloping surfaces, with regular to irregular morphology, where tectono-structural and erosive processes prevail,
and may be defined by planes (strata, foliation, diaclasis, among others), either arranged in the opposite direc-
tion to the slope of the terrain (counter-slope) or in favor of the slope of the terrain (structural slope). They can
be long to extremely long, whose slopes, being of structural origin, are around steep slopes (45–54.9°) (adapted
from SGC, 2012 and Sánchez, 2014).
13 Structural origin saws Sos
Topographic promontories of mountainous and elongated morphology with long to extremely long slopes,
mostly straight, with very steep to abrupt slopes, where tectono-structural processes and erosion or accentu-
ated mass movements prevail. It corresponds to the Andes Mountain Range (adapted from SGC, 2012).
14 Anthropo-
genic envi-
ronment
Artificial channel Aac Channels constructed for dredging, rectification of channels for channeling the Macul stream in urban areas
and locally for water supply (adapted from SGC, 2012).
15 Slagheaps Asl
All types of solid waste resulting from demolition, repair of buildings or construction of civil works, i.e., the
leftovers of any action carried out on urban structures. In which the disposal process can be technical or non-
technical (adapted from SGC, 2012)

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16 Mining or extraction of
alluvial sediments Aemc
These are extensive areas dedicated to the open-pit extraction of materials and minerals, whose extraction pro-
cess is carried out on the surface of the land. It includes terraces made on hillsides for the extraction of construc-
tion materials such as blocks, sand and gravel, coming from alluvial fans, where it is also settled (adapted from
SGC, 2012).
17 Agricultural terraces or
grading areas Aatg
Modified and modeled surface on alluvial fans of the Macul basin, with the purpose of building housing and
infrastructure necessary for the population. They are made up of materiality of variable origin, whose settle-
ment are flat areas with large areas covered with concrete, and to a lesser extent with green areas and areas de-
void of vegetation (adapted from SGC, 2012).
18 Urbanized areas Au
Modified and modeled surface on alluvial fans for the purpose of building housing and infrastructure neces-
sary for the population. They are made up of materials of variable origin and are built in flat areas with large
areas covered with concrete, and to a lesser extent with green areas and areas devoid of vegetation.

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Figure 6. Multitemporal map of landform of the total Macul basin. The black arrow indicates changes in temporality.

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Regarding the morphometric analysis, this is made up of the parameters of Shape,
Drainage System, Relief, and Complementary. All this with the objective of inferring the
hydrometeorological response of the Macul basin:
Shape parameters (Table 6): A basin with an area (A) of rainwater catchment of 23.5
km
2
is obtained, representing the second largest area basin in the entire foothills of the
Santiago mountain range, only surpassed by the San Ramón basin (Figure 7 and Appen-
dix A1). According to the Horton Form factor (F) classification [66] and the compactness
factor classification (Kc) [67], they indicate that the Macul basin (QM) is a widened basin
with a short main channel and an intermediate shape between round-oval and an oblong
basin, with the consequence of having a tendency to concentrate the runoff of an intense
rainfall; easily forming large flow because the relative distances of the points of the divide
with respect to a central one does not present major differences and the time of concen-
tration becomes shorter.
Table 6. Results of the Form Parameters for the Macul basin.
Form Parameters
Name Results
Basin Area (A) [km
2
] 23.5
Basin Perimeter (P) [km] 21.6
Axial Length (A
l
) [km] 7.1
Length of the main channel (Lc) [km]
7.8
Form Factor (F) (Horton. 1932) 3
Compactness Factor (Kc) (Gravelius. 1914) 1.3
Figure 7. Macul basin, where the topographic map is shown, in addition to the result of the delimitation and obtaining of
the perimeter and area of the basin and the generation of the drainage networks according to their orders based on the
methodology of Strahler [68] by means of morphometric analysis.

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Drainage network parameters (Table 7): They resulted in a basin with drainage orders
from 1 to 5 according to Strahler’s methodology with predominantly dendritic and paral-
lel patterns in the upper zones of the basin, which reflect different runoff regimes in the
basin (Figure 6). On the other hand, according to the classification of Gil et al. [69], Sen-
ciales [70], Sala and Gay [71], and Sanchez [72] with respect to the Bifurcation Ratio (Br)
and Length (Lr), this indicates that the basin would present a significant rapidity of flow
waves, and also confirms that it is a rounded basin with a greater concentration of runoff
along the main channel; these values usually represent the highest flow hazards due to
sudden concentration of runoff.
Table 7. Result of the morphometric analysis of drainage system parameters.
Drainage System Parameters
Name Results
Drainage order (n) (Strahler, 1964) 1, 2, 3, 4 and 5
Bifurcation ratio (B
r
) (Strahler, 1964)
1.8
Length Ratio (L
r
) (Strahler, 1964) 0.9
Density of the drainage network (Dd) (Hor-
ton, 1945) [1/km] 6.1
Drainage Frequency (F) (Ordoñez, 2011 in
Garay & Agüero, 2018) [1/km
2
] 40.3
Drainage hierarchy (J) 5
Relief Parameters (Table 8): They indicate that the Macul watershed has an absolute
unevenness (H) of 2066 m a.s.l., in addition to having an average slope (Sm) of 62.3%
(31.2°) and maximum and minimum slopes of 276.3% (71.1°) and 0%, respectively, which
can have repercussions on important rainfall runoff velocities, which can drag important
sedimentary material towards areas of lower slope (Figure 8). On the other hand, the Hyp-
sometric Curve (Figure 9), according to Guerra and González [73], allows estimating the
state of potential dynamic equilibrium of the basin, under the hypothesis that this function
relates altitude with area, therefore it changes with time as the basin undergoes denuda-
tion; on the other hand, it can relate the differential activity between the processes of tec-
tonic construction and degradation by erosion, activities not necessarily related to the age
of the basin. The results indicate that the Macul basin (QM) is in an intermediate phase
between a mature basin and a young basin, which in turn can be related to the relationship
with the tectonic uplift of the Andes Mountains representing the endogenetic processes
that affect it, together with the modeling of the surface through exogenetic processes,
which translates into the denudation and alluvial and fluvial environment of the basin,
represented by the presence of active transport of the basin to smaller areas.
Table 8. Result of the morphometric analysis of relief parameters.
Relief Parameters
Name Results
Absolute elevation difference (H) [m a.s.l.] 2066
Average slope of the basin (Sm) [%] 62.3
Maximum slope of the basin (SM) [%]
276.3
Minimum slope of the basin (Smin) [%] 0
Hypsometric curve (Strahler, 1964) -

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Figure 8. Morphometric maps of the Macul basin, Metropolitan Region (Chile). (A) It represents the topographic map with
units m a.s.l. (B) Map of slopes in units of degrees. The topographic profile represents the height trends of the main chan-
nel, related in turn to the location of some urban areas.

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Figure 9. Values and graph of the hypsometric curve for the Macul basin.
Complementary parameters (Table 9): The results of Tc, Ie, and Sc according to the clas-
sifications of López and Romero [56] Aracena [74], and Garay and Agüero [75] indicate
that the Macul basin (QM) presents torrential characteristics, in addition to presenting
more favorable conditions for the triggering of debris flow or alluvium processes, present-
ing a high density of drainage per basin surface, allowing rapid runoff towards the main
channel of the basin, decreasing the infiltration capacity of the basin. In addition, Pi, ac-
cording to Borguel’s classification [76], indicates that the basin has a high capacity for
sediment accumulation, and therefore a high availability of sediments, which can result
in significant sediment transport to areas of lower slope in the event of a hydrometeoro-
logical event.

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Table 9. Result of the morphometric analysis of complementary parameters.
Complementary Parameters
Name Results
Torrentiality coefficient (T
c
) (López and Romero, 1987) (1/km
2
) 20.3
Basin Efficiency Index (I
e
) (Aracena, 1993) 16.6
Potentiality index (P
i
) (Börgel, 1978)
2.2
Storage Coefficient (S
c
) (Garay & Agüero, 2018) 0.5
Finally, the geology, the Macul basin (QM) is characterized by consolidated and un-
consolidated units, (Figures 10 and 11), where a result and description of each one can be
found in Table 10. The large areal extension of Tia stands out, making up 79.9% of the
basin area, however, if we take into consideration the total area (basin area and mouth
area), this unit represents 43% of the total area. The importance of characterizing this for-
mation lies in the fact that part of its area represents exposed rock in the basin, equivalent
to the area of direct rainfall runoff (53% of the formation). On the other hand, the rest of
the area is made up of unconsolidated sedimentary units, represented by the materials
found in the alluvial beds (Qa, Qai) and on the slopes of these watersheds (Qac, Qc, Qrm),
being deposited on top of a consolidated rock unit (Tia). These materials are characterized
by having a varied origin and above all for not being consolidated and for presenting a
heterogeneity in their composition and particle size; therefore, they do not present a re-
sistance to downslope displacement once the alluvial flow has developed and are likely
to be constituent material of these flows. The predominant unit in this case is the colluvial
deposits (Qc), which represent 9% of the basin area. Now, if we consider the basin as a
whole, the piedmont deposits (Qap) would be the predominant ones, represented by 43%
of the total area (Figure 9) however, the delimitation of this area is approximate [9], so this
percentage can vary. It is affected by faults that affect the Abanico Formation and part of
the unconsolidated sedimentary deposits, highlighting the active San Ramón Fault, whose
movement is reverse of west vergence with a preferential NS trace.
Table 10. Geological units belonging to the Macul basin.
Code Description
Qa
Active alluvial deposits (Holocene): Fluvial and alluvial clastic sedimentary deposits filling active
ravines and gullies where some streams flow, whose deposits come out on less steep areas known
as piedmont (Qap and Qap 1993). These deposits are composed of non-consolidated to slightly ce-
mented and apparently unlayered gravel, sand, clays, and silt, having variable thicknesses and
showing grayish-brown colors. Gravel deposits are predominantly matrix-poor, and they contain
polymictic and polymodal angular and subangular clasts with moderate sphericity, mainly coming
from Abanico Formation (adapted from Moreno et al., 1991 and Naranjo & Varela, 1996).
Qac
Alluvial and colluvial deposits (Holocene): Active and inactive alluvial and colluvial non-consoli-
dated clastic sedimentary deposits, which are primarily located on active ravines and at the foot of
the slopes. These deposits are composed of gravel, sand, silt, and clays to a lesser extent. The gravel
is polymodal, occasionally matrix-rich containing subrounded to angular clasts, furthermore its li-
thology is influenced by the surrounding rocks, especially by the ones from Abanico Formation.
The matrix proportion is variable and composed of grains ranging from clayey silt to sand showing
grayish-brown colors (adapted from Moreno et al., 1991).
Qc
Colluvial deposits (Holocene): Diamictic clastic sedimentary deposits that have a highly heteroge-
neous granulometry ranging from boulders to clayey-silty matrix with angular clasts, whose litho-
logic composition corresponds to the surrounding rocks. The amount of matrix is higher than the
amount of clasts, being, therefore, matrix-rich. These laminar deposits develop steep slopes around
20 to 25° at the foot of the exposed flanks setting up thick cone-shaped piles, which in some cases
reach tens of meters. Created by mechanical and chemical weathering. Its age is primarily Holocene
(adapted from Moreno et al., 1991).

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Qap
1993
Piedmont alluvial deposits 1993 (Holocene): Represents the technical record of the urban area af-
fected by flows of alluvial sediments on 3 May 1993. They are represented by torrential-alluvial
clastic sedimentary deposits which are fining-upward from the apex of the alluvial fan to its distal
zone, due to the energy dissipation caused by the spread of the flow at a less steep slope. The de-
posits reach an estimated volume of 1 × 10
6
m
3
with a volumetric concentration of 40%, liquid and
solid flow of 72 m
3
/s and 48 m
3
/s, respectively. They are composed of mud and debris flows includ-
ing clays, silt, sand, and gravel with boulders of up to 5 m in diameter, eucalyptus trunks, and an-
thropogenic material as well. Some records show the development of two main flow waves, each of
them having particular features; the first flow wave was 1 m high (<1.2 m) reaching speeds close to
15 km/h and sweeping rock boulders of up to 1 m in diameter, eucalyptus trunks and grayish mud
along. The second wave was made up of mud and debris flow that surpassed 3 m in height reach-
ing speeds up to 30 km/h, being this one the most harmful wave (Ayala & Cabrera, 1996).
Qap
Piedmont alluvial deposits (Holocene): Torrential-alluvial clastic sedimentary deposits arranged in
various alluvial fans covering from the apex of Macul basin and its ravines that cross the western
part of the Andean Range and join to each other on the middle and distal part to set up an only
sloping surface. The sediments are comprised of sandy gravel with some alternating sand beds that
show a decrease in the coarser grains size from 1.5 m in diameter in the apex of the fans to 1 m in
the middle part. The grain size keeps diminishing to the distal zone, increasing in turn, the amount
of sand. Internally, they are poorly or non-layered. The origin of these deposits is given by the inter-
mittent torrential input from high energy water streams, which interfingers with newer deposits,
just like the piedmont alluvial deposit of 1993 (adapted from Moreno et al., 1991 and Naranjo &
Varela, 1996).
Qai
Inactive alluvial deposits (Pleistocene—Holocene): Alluvial and fluvial clastic sedimentary depos-
its, which fill ravines and gullies where some streams flow, developing low slopes and inactive al-
luvial fans. It is comprised of gravel, sand, silt, and clays to a lesser extent, developing stratification
surfaces locally and variable thicknesses. Gravel is mainly matrix-rich, having polymodal grains
from 1 cm to 3 m, subrounded and polymictic, comprised predominantly of Abanico Formation
clasts. The matrix is composed primarily of coarse sand to grayish-brown silt-clays. To the top, it
shows the development of vegetation and a soil horizon (adapted from Moreno et al., 1991).
Qrm
Landslide deposits (Pleistocene—Holocene): Clastic sedimentary deposits formed due to land-
slides that affected rocks, debris, or soils in moderate to steep slopes. Comprised of diamictic sedi-
ments of angular clasts, polymodal and monomictic. The clasts are surrounded by a matrix mainly
composed of a mixture of sand, silt and, clay. The thickness varies depending on the deposit loca-
tion and the deposits show brownish-yellow colors, which are a distinctive feature. The age ranges
from the upper Pleistocene to the Holocene (adapted from Moreno et al., 1991 and Naranjo &
Varela, 1996).
Tia
Abanico Formation (Upper Cretaceous to Lower Tertiary): Stratigraphic sequence of sedimentary
and volcanic rocks, the latter are tuff and volcanic breccias having alternating gray-brown to violet
grayish-red effusive volcanic rocks, which in some close areas have an estimated thickness of 3000
m. Particularly, in some areas there is a development of regolith that could or not have vegetation.
Its Upper Cretaceous to Lower Tertiary age is given based on its stratigraphic relationships and fos-
sil-bearing interbedded sedimentary rocks (adapted from Thiele, 1980).

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Figure 10. Areal analysis of the geological units of the Macul basin. (A) Basin and mouth area. (B) Only the Macul basin.
Figure 11. Geological map of the Macul basin, showing the different geological units of unconsolidated sediment and rock
units that make up the basin and the mouth area. (A) Plan view of the geological map. (B) Relief view of the geological
map.

Sustainability 2021, 13, 2501 26 of 44
3.2. Built Environment
3.2.1. Water Pipelines and Critical Hydraulic Infrastructures
It is often argued that the Zanjón de la Aguada is born in QM and corresponds to one
of the main natural channels of the Greater Santiago metropolitan area [77]. However, the
history of the area suggests that this is not exactly the case, but instead the result of new
water pipeline systems and hydraulic infrastructures that interacted critically with the
geological environment of the basin already described.
Historical sources refer to the connection of QM with the Zanjón and also the con-
struction of a channel to connect the Maipo River with the Mapocho to avoid agricultural
droughts [78] (p. 91). In 1742, it was already indicated that there was a need to open up a
ditch in the foothills of Macul to this end (Figure 12). In 1772, it was pointed out that there
was “a ravine over which it was necessary to build an aqueduct that was to join the south-
ern and northern rivers [...] which was also open, over an extension of several blocks, with
very little time left to reach the Zanjón” (Emphasis added) [78] (p. 46). Around 1820, it
was insisted that “six drains be opened from the Ugareta gully to the Mapocho, in the
watering hole [...] in the Macul estuary [...] and at other points as necessary to prevent the
flows” (Emphasis added) [78] (p. 84). Furthermore, in 1861, the indication of a “channel
to be opened to the waters of the stream” was reiterated (Emphasis added) (Figure 13).
Figure 12. 1742 Plan of the land between the city of Santiago and the Maipo River with various projects to bring water
from the high river to the city. At the center of the image there is an estuary represented in yellow that says “Plain where
the ditch must be opened up to the skirt of Macul” [79].

Sustainability 2021, 13, 2501 27 of 44
Figure 13. 1861 Drawing of the Macul farm of the testamentary Mrs. Mercedes Gandarillas de Larraín. It can be seen the
basin, QM and the “channel to be opened to the waters of the stream” downstairs [80].
Although the exact date when Zanjon joined the QM estuary is unknown, by the end
of the 19th century its connection was established resulting in an inundation of problems.
In 1899, “Neighbors of San Miguel detected that the cause of that [flows] was the conver-
sion of the trench, at the level of the chacarilla of Macul, into a channel for irrigation...
reason why it had stopped being a natural drainage” [81] (Emphasis added) (p. 2). Inun-
dations left dozens of victims and fatalities [82] and continued to be a hazard in the 20th
century. In 1982, a flow collapsed the Las Perdices bridge (Interview J.A., July, 2019) and
in 1984, the irrigation channel burst [83]. The disaster of 1933 ended up causing the over-
flowing of the three main channels.
In addition to the construction of bridges and canals in the mouth area, local histories
and accounts indicate that during the 20th century, the owner of Fundo [estate] Las Pircas
built a dam in the ravine for fish farming and the operation of the “Quebrada de Macul
Drinking Water Plant” [84] (This water plant was destroyed by the 1993 event, and re-
placed by one built a few meters below the vestiges of the original. According to Aguas
Andinas [water utilities operator] it was built to supply drinking water to the residential
sector of Las Pircas (Observation Notes, August, 2020).
In summary, Zanjón de la Aguada was originally a natural stream of drinking water
for Santiago that began to be intervened for agricultural purposes around the 19th cen-
tury. This anthropic intervention resulted in early inundations in the eastern and western
areas of Santiago. These interventions were part of a larger network of canalizations and
hydraulic infrastructures that were built in the 19th and 20th centuries in Santiago’s pied-
mont. The plans carried out to connect the Maipo and the Mapocho rivers—which in-
cluded management protocols, hydraulic works, and water catchments—interfered criti-
cally with the geological environment through the modification of alluvial deposits, nat-
ural riverbeds, and the hydrological regime of rivers. These interruptions were critical
elements influencing the characteristics, intensity, destructive power of the flow, and scale
of future alluvial events.
3.2.2. Piedmont Urbanization
The urban expansion in the piedmont sharpened the effect of the previously men-
tioned hydraulic interventions. Urbanization began in 1952, initially unfolding in the
northwestern limit of the basin. In the 1960–1982 period, the rate of urban development
increased significantly [23]. This forced, in 1984, the expansion of the municipality’s urban

Sustainability 2021, 13, 2501 28 of 44
limit [10], an expansion that did not account for the hydro-geological particularities of the
territory [85]. Thus, by 1993, the study area was not only occupied by large hydraulic in-
frastructures, but also by an expanding urban population [10] that shared the territory
with remaining informal settlements that located near the riverbed as a result of a general
pattern of illegal land occupation that began in the 1960s [86].
It is important to highlight that even after the 1993 event, urban expansion has con-
tinued, and even intensified. After the disaster, informal settlements were relocated [10]
and exclusion zones were enforced [23] following new land use codes that demanded mit-
igation measures for any new construction near the watercourse [87]. The result, rather
than moderating the area’s urbanization, was a sharp increase in residential developments
in the QM zone, particularly in the 1992–2012 period [87]. In 1998, the “Santa Sofía de
Macul” real estate project was approved, “marking the beginning of large-scale urbaniza-
tion of the Florida foothills, replacing nearly 250 hectares of native vegetation with hous-
ing” [88] (p. s/n). At the same time, the construction of “Las Pircas” project began on the
north bank [89] of the QM basin, and in 2004 the “Lomas de Lo Cañas” project, located by
the Santa Sofia Creek’s excretion cone south of QM [88] also began its construction.
As a result, by 2005, the Macul-San Ramón basin had the highest levels of urban oc-
cupation in eastern Santiago [12]. By 2018, it was estimated that residential land use of the
area was 1591.9 hectares [87]. Rural roads continued to be paved to ensure “the normal
runoff of water and the protection of the edges and slopes” [90] (p. 111). Today, according
to modifications intended to be made to the District Regulatory Plan, the urbanization of
foothills could continue [91].
In short, the accelerated process of urbanization of the piedmont interacts problem-
atically with the hydro-geological conditions of the area. Urbanization implies the defor-
estation of the vegetal cover and waterproofing of the soil cover that directly affect the
infiltration time, amount of direct stormwater runoff, and sediment quality that can be
displaced from the mountains [12]. Although urbanization ideally requires reforestation
and permanent protection of riverbanks, the decisions related to urban planning show
that its risks have been made invisible through the prioritization of real estate projects
becoming an important source of risks for the inhabitants.
3.2.3. Mitigation Works
As a result of the 1993 disaster, the Directorate of Hydraulic Works (DOH) conducted
a study for the construction of protection infrastructures for urban areas surrounding the
alluvial channel of the river mouth. This consisted of seven alluvial control structures lo-
cated exactly in the limit between Peñalolén and La Florida districts. The latter involved
the modification of the riverbed trajectory and the construction of decanting infiltration
pools placed along 1590 m, with an estimated storage capacity of sediments and clasts of
70,000 m
3
[87].
The construction of mitigation works considered historic parameters, taking into ac-
count a volumetric concentration around a 38% and a detritic flow of 75 m
3
/s. However,
research [9,17] has estimated that the volume of deposits registered in the 1993 alluvium
was 840,000 m
3
, that is to say, significantly superior to the actual retention capacity. For
this reason, in 2018, DOH began a process of excavating a larger decanter on the south
side of the main channel of the stream [92] (The works considered (a) Slope retaining
walls, (b) System of torrent correction dikes, (c) Retention system in hollow, (d) Improve-
ment of decanting pools, (e) Canalization with stone masonry and (f) Construction of Las
Perdices Avenue Bridge [93].

Sustainability 2021, 13, 2501 29 of 44
3.3. Socio-Cultural Environment
3.3.1. Geographic Memory of QM and First Settlements
The geographic memory of QM and the first settlement locations show a complex
socio-cultural environment that is in many ways at odds with the geological features of
the area and its associated risks. According to local accounts, the alluvial channel emerges
dynamic in form, time, and space. As the oldest neighbor said, “By the year 1938, 1940,
the creek was not large, because all the small alluviums, which have always occurred, had
scattered [the creek] along the pastures” (Interview O.Z., July, 2019). Confirming this dy-
namism, another informant pointed out that the creek was different in its spatial charac-
teristics, changing locations over time: “When I arrived to this sector, I had contacts with
the ancient people, they say that the Macul ravine had run from Quilin to where it is now”
(Interview J.A., March, 2020). Other accounts evoked a ravine located on Los Presidentes
street (Observation Notes., September, 2020), and the toponymy of QM street also indi-
cates a northern location.
Other evidence of a dynamic channel is found in the field tests carried out in the
sector at the end of the 1980s. Before building a complex on Quilín Street—north of QM—
one informant told us that in soil tests “a lot of different material came out, including sand,
pebbles, like the same [type of soil] when a river passes” (Interview J.A., March, 2020). He
added that when the urbanization of QM Street began, “they couldn’t lay pipes because
they found a sand bank” (Ídem). Another informant said that QM morphology was not
the same: “It was more here […] It was not right as it is now” (Interview A. C., July, 2019).
When we asked if the flow itself had caused the transformation, he replied “No, the can-
alists who made the detour changed it [...] just as they made bridges, they made every-
thing new” (Ídem). He was referring to the mitigation works carried out after the disaster.
This report is consistent with the first settlement location according to ethnohistorical
records. When the Spanish colonizers arrived, Macul alluded to an indigenous village lo-
cated in the space they called “comarca” of Ñuñohue. These towns, also called “pueblos
de indios” [Indian towns], were sectors located in “parts of valleys or ravines, near rivers
or water holes” [94] (p. 30). In fact, the settlement was located north of the current alluvial
channel in the coordinates 33°30′–70°34′ [95] where two spring waters came from a slope
of the mountain range [96] (p. 121). As indicated in the plan from 1614 (Figure 14) there
was a “ditch that comes from Macul” that “[...] goes up to the skirt of the mountain range
that could be wide beynte [twenty] quadras and long” [96] (p. 121). Although it has been
suggested that these waters came from the San Ramón ravine [96], the georeferencing and
historical maps of the town of Macul suggest that the ravine could be part of QM old
natural channel.

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Figure 14. 1614 Plan with the location of the ditches that watered the lands of the cacique Martín de Macul [96] (p. 120).
The 16th century was a time of upheaval for indigenous peoples due to the establish-
ment of the encomienda system and land grants, which enslaved the indigenous population
and gave ownership of lands and waters to the Spanish colonizers. The indigenous town
of Macul survived as an Indigenous settlement until the 18th century, a period in which,
however, it was common to see old roads intervened, new bridges built for the passage of
wagons, old irrigation ditches widened, and water courses changed for irrigation [95].
This meant a subdivision of land and intensification of agricultural productivity, giving
way to a built environment that radically modified the old indigenous hydraulic struc-
tures, socio-territorial organizations, and ecological relationships.
In other words, the geographic memory of QM indicates that its natural channel
would have been located in a different place from the current one due to early anthropic
modifications. This makes sense with the triangulation that can be made between the eth-
nohistorical information of the first indigenous settlements, local memory, satellite images
of the alluvial fan, and the areas of restriction indicated by the Communal Regulatory Plan
(For more details see Santiago Metropolitan Ordinance Plan: https://ci-
perchile.cl/pdfs/2015/03/mineria-maipu/PRMS.pdf (accessed on 10 October 2020). or
PLADECO Peñalolén 2013–2016: https://www.penalolen.cl/wp-content/up-
loads/2016/10/DIAGNOSTICO-COMUNAL.pdf (accessed on 10 October 2020). And/or
“Informe Consolidado de la Evaluación de Impacto Ambiental de la Declaración de Im-
pacto Ambiental del Proyecto Modificación PRC Peñalolén”: https://in-
fofirma.sea.gob.cl/DocumentosSEA/MostrarDocumento?do-
cId=3b/b9/f056be499fc09a8f5f8f0ddc907f13fa0a1f (accessed on 10 October 2020)) that
show a secondary branch of the ravine in a northern direction. Likewise, after the allu-
vium, the riverbed was artificially modified, changing again the natural channel direction.
3.3.2. Memory of 1993 Alluvium and Perceptions of Risk
Memory and risk perceptions illuminate the tensions between the geological, built,
and socio-cultural environments described above, and the way local organizations make
sense of them. When 1993 survivors remember the disaster, they explain it as a shared
responsibility: Nature and human.
Neighbors are well aware of the anthropogenic root-causes of the disaster. As one of
them said: “it has never been made explicit that man (sic) is also to blame, so don’t come
and say ‘nature, nature, nature’” (Interview J.A., July, 2019). In fact, doing field visits with

Sustainability 2021, 13, 2501 31 of 44
them (Figure 15) they indicated how the territory has changed over time: “Before there
were farms...And up on the place where they take out gravel now, there were pastures”
(Interview N.A., July, 2019). He continued: “That’s the Las Perdices bridge... A tiny bridge
that lasted ten minutes before being taken away [by the 1993 landslide]... If those bridges
had been expedited, and if it had been cleaned up there, this [destruction] would have
been much less” (Interview J.A., July, 2019).
People also remember the calicheras, or sand pits above canal Las Perdices that were
exploited by local families and part of the precarious local economy. These calicheras
played a critical buffering role: “when it rained the water did not run straight down the
stream, but filled the calicheras with material” that would otherwise be dragged down by
the flow (Interview J.A., July, 2019). However, these calicheras were banned in 1973. In
lieu, in 1981, a larger sand extraction plant was built, increasing the exploitation surface
area and the volume of extraction consecutively [88]. This operation altered the riverbed,
exposing the accumulated material to runoff events. Another neighbor, reflecting on the
rocks from the pavement of old riverbeds that the landslide dragged down the streets,
asserted vividly: “the stream always asks for what was hers” (Interview A.C., June, 2019).
Figure 15. Activities done in the research site with neighbors and civil organizations. (A) Tour guided by old inhabitants.
(B) Excursion with BEAF—Florida High Forest Brigade. (C) Neighbor drawing of the basin, vegetation, and critical infra-
structures. (D) Neighbors sharing maps of floodable park project in a communal activity.
In sum, survivors suggest that when the geological environment interacted with an
ill-planned built environment, the alluvium became a disaster. In spite of this, the exclu-
sion zones defined after the flows impacted were arbitrarily made, and the urbanization
of the piedmont contradictorily increased. Neighbors indicate that after the flow, the ex-
clusion zone of La Higuera—one of the most affected sectors—was defined “to the taste
of the consumer” (Interview S. P., June, 2020), that is prioritizing real estate considerations
instead of community safety. Actually, they remember that one time the mayor of La Flor-
ida, reacting to the community’s call for a better post-disaster planning, said defiantly
about the definition of the exclusion zone: “‘If I get angry, I will draw a line like this, like

Sustainability 2021, 13, 2501 32 of 44
this,’ in a zigzag, and he scratched like this, and that’s how it was” (Interview S. P., June,
2020).
In this regard, local organizations claim that urban planning has made risks invisible
as a result of real estate pressure. “how do they authorize all that,” they ask, “how do they
authorize the construction of houses a meter and a half away from a ravine?... they have
no idea of the consequences, there are schools and infant schools half a block from the
stream… the drains are just not enough” (Interview N.A. & J.A., July, 2019). New residen-
tial projects, moreover, have not replaced the original vegetation cover with a proper re-
forestation process (Figure 16).
Figure 16. State of reforestations in the south west of Alto Macul real estate project. Source: Authors’ photographic archive.
As a response to these conflicts and gaps, community organizations have imple-
mented different risk reduction strategies, establishing multi-sectoral collaborations. In
fact, they invited us to participate in the communal emergency plan whose main objective
is to elaborate a “Protocol for Emergencies and Disasters limited to the territory, updated
and specific to the local reality, which will define the organization and responsibility to
act in situations of Emergencies and Disasters” [97] (p. 4).
In sum, our results suggest that the disaster of QM cannot be understood from the
geological environment alone. The socio-cultural environment, composed of memories
and social perceptions of risk, shows how the geological and built environment interact,
within the specificities of local occupational patterns, in the compounding of the disaster.
4. Geo-Social Model: Mapping Environmental Interactions in the Macul Basin
As an exploratory methodology that seeks to render visible, through transdiscipli-
nary processes, the interactions between the geological, built, and socio-cultural environ-
ments, the Geo-Social Model can be translated into a geo-social map of the Macul Basin
(Figure 17). This map, as an exercise in making the complexities of the territory public,
contributes to a better understanding of the alluvial phenomenon, and hence emerges as
a relevant conceptual and methodological tool for landslide risk reduction and prevention
in the future.

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Figure 17. Geo-social map of the discharge (or mouth) area of the Macul basin, Metropolitan Region (Chile).

Sustainability 2021, 13, 2501 34 of 44
The geo-social map (Figure 17) shows and synthesizes an evident intersection be-
tween the three environments. The estimated perimeter of the mouth of the alluvium—
that is part of the geological environment—overlaps with the built environment because
it is mostly urbanized (PUA and AU) except for the few agricultural and grading areas
that remain in the area (AATG). In addition, as we already showed, the artificial channel
Zanjón de la Aguada (ZDAC) intercepts perpendicularly with the two main water chan-
nels of the study area—Canal Las Perdices (LPC) and San Carlos (SCC)—forming the crit-
ical area of the disaster where, in effect, is the alluvial fan of the 1993 event (FAF 1993). In
this area, hydraulic infrastructures identified (MAB and MIB) are critical due to the earlier
connection established between the QM and the Zanjón de la Aguada, which is estimated
according to historical records in the 19th century. It is also visualized that the zones of
restriction or exclusion of construction (EEEZ and LHEZ) are inhabited by old houses and
a recent informal settlement (TD) as evidenced by the socio-cultural environment. The
zone of mining extraction (AMEAS and ASMEZ), which is part of the built environment,
currently covers an area of 365,886 m
2
of the alluvial fan and can increase the detritic ma-
terial of the alluvial flow and therefore its destructive power because of the unconsoli-
dated material and its location close to the main channel. Upstream, at the apex of the
river mouth, is the drinking water plant (PWP), considered as a critical infrastructure that
can provide solid and liquid material, as it is exposed to the trajectory of a possible alluvial
flow, due to its location and for not containing protection works.
Mitigation works (MCL_NE, MCL_SW) located in the southern zone of the mouth
area, have a preferably southwestern trajectory, and form the so-called artificial channels
(AAC). This particular trajectory represents a problem in terms of the lack of protection
of the northern area of the alluvial fan (FAF), which in turn is made up of agricultural
areas and mainly urbanized areas (AU) whose construction is relatively recent. This is
because according to estimates based on geological evidence (Deposits of piedmont and
alluvial fan, FAF 1993) and social evidence (Testimonies I_JA, I_OZ, ON and MIV ethno-
historical sources), the natural trajectory of the channels is possibly in a west and north-
west direction, specifically along Quilin Norte street, and areas near Los Presidentes Av-
enue mainly coinciding with the Las Pircas neighborhood (channel geo-social location).
More proof of this is the ethno-historical evidence reported by the socio-cultural environ-
ment, which indicate, based on geographical coordinates of the historical record, that the
indigenous settlement of Macul (MIV) was located in the western area of the mouth of the
river, coinciding with Quilin Norte street (I_JA). To this is added that the indigenous peo-
ples used to be located in sectors bordering the natural trajectories of water, which allows
us to conclude that the natural course of QM is coincident with the area mentioned above
(I_JA). In other words, both the current riverbed and the mitigation works are part of a
built environment that comes into conflict with the geological and socio-cultural environ-
ment of the area of study, this could lead to socio-natural disasters if are not considered
in the future urban planning.
5. Discussion
Although several research studies have been developed around landslides [52–54,98–
101], there is still a need to deepen the understanding and characterization of their main
conditioning and triggering factors and their in a context of anthropogenic intervention.
Based on this, from the geological discipline, several investigations have been carried
out in the Macul basin, inspired mainly by the great impact on urban areas of the alluvial
event of 1993 and the subsequent minor alluvial activations in the basin. For instance,
Naranjo and Varela [17] conducted a geological analysis of the causes, mechanisms, and
effects of the 1993 event, inferring that the main conditioning factor was the large accu-
mulation of unconsolidated sediments in the basin, which came from previous events de-
posited mainly in the alluvial channels, and inferring that the intense rainfall was the main

Sustainability 2021, 13, 2501 35 of 44
triggering factor. However, like this research, Ayala and Cabrera [9] indicate that the de-
velopment of landslides is not only influenced by unconsolidated sediments, but also by
the characteristics of other triggering factors.
The latter was the first research studying the vulnerability of certain urban areas in
relation to areas possibly impacted by flow-type landslides. In this regard, Naranjo and
Varela [17] made a zoning of the 1993 impact area in Macul with field data and Garrido
[102] zoned areas for possible impacts using LAHARZ and MSF (Modified Single Direc-
tion Flow Model) algorithms, giving results relatively close to the zoning provided by
Naranjo and Varela [17]. The MSF model shows the three most probable directions for
impact by flow-type landslides, which are quite close to the actualized results provided
by the geo-social map. On the other hand, Martínez [21], uses the Weighted Map Overlay
methodology with the IS Susceptibility Index by applying a methodology of Lara [58],
making an advance in the application of conditioning factors, but disregarding within
these the anthropogenic influence on its development.
As can be seen, although these investigations represent an important advance in the
knowledge of these factors, there is still a lack of consensus in the determination of the
main determinants of river landslides. However, the morphometric analysis is in a certain
way complementary since it gives good results in terms of determining the response of
the basin in a quantitative way, which confirms what was delivered in the geological anal-
yses and by landform regarding the fact that the Macul basin (QM) has optimal character-
istics for the development of debris flows [56,69,71,77]. In addition, its results can be used
as a complementary analysis or as a qualitative method validation methodology, taking
into account that the greatest weakness of this analysis is its absolute dependence on the
quality of the digital elevation model, in addition to the inaccuracy of ranges inherent to
any analysis.
Additionally, they tend to underestimate the anthropogenic influence in the devel-
opment and magnitude of the impact of threats due to the difficulty that this entails. In
this scenario, the problematization of flow-type landslides through the Geo-Social Model
and a transdisciplinary approach can help to clarify this conundrum, providing advances
in the way landslides are understood and assessed.
In general, even though many studies recognized the role of humans in landslide
processes, there are few reviews about this topic; and conceptual and methodological
problematizations [103,104]. Indeed, landslides are more commonly attributed to have
been caused by heavy rainfall [4], but as the results of the Geo-Social Model show, land-
slides—particularly in urban contexts—are often the result of anthropogenic disruptions
of natural balances and systems. This is coherent with other studies carried out recently
worldwide that started to conceptualize landslides as Human-Induced Landslides (IHL)
that is to say, events that are “triggered or partially aggravated by anthropic activities”
[104] (p. 217).
More specifically, the results of the built and socio-cultural environment are oriented
in this direction showing that anthropic activities are the result of interventions that are
the effect of long histories of infrastructuring, urbanization, and occupation of the geolog-
ical environment that while exceed the memory of current inhabitants, are passed inter-
generationally, and registered in the material and cultural trajectories of the community
and its perceptions of risk.
In first place, infrastructuring took form in QM via water canalizations that changed
the natural channel for agricultural purposes in a long-term duration perspective and also
through the construction of critical hydraulic infrastructures. In this regard, QM research
does not point out histories of infrastructuring and its influence in landslides; from a
worldwide perspective, there are few examples that account for these important trigger-
ing factors but they are coherent with the Geo-Social Model results. For example, in Bel-
gium, Preuth et al. [105] has shown that water pipes crossing active landslides caused
deformations increasing the negative effect of water. In addition, Jaboyedoff et al. [104]

Sustainability 2021, 13, 2501 36 of 44
confirm that small modifications of slope topography or diversion of a surface water col-
lector may induce landslides in many cases. Additionally, river erosion caused by modi-
fication of the course can produce landslides because it can change the course or the debris
flow initiating new erosion banks which can promote landslides [106,107]. As Sepúlveda
and Petley [108] have argued, this lack of evidence may be explained due to a research
deficit in Latin America and the Caribbean, where the mechanisms are not yet well un-
derstood, distribution causes and triggers of landslides.
Secondly, the rapid urbanization process experienced in QM evidenced occupation
of hazard prone areas and pavimentation of original rural roads extending as a main re-
gional problem has already been pointed out by national research and local organizations.
The latter can be understood in low- and middle-income countries as a consequence of a
badly planned and poorly managed urban expansion [109]. In effect, it is well known that
landslide vulnerability in mountain environments is increased in dense urbanization ar-
eas and/or where precarious squatter settlements have developed at the foot of slopes
[3,4,26,108,110,111].
Thirdly, the geographic memory of QM indicates—for the first time—that its natural
channel would have been located in a different place from the current one due to early
anthropic modifications. Furthermore, the local memory of the event indicates the anthro-
pogenic root—causes of the disaster, and social perceptions of risk show both the defi-
ciencies of urban planning but also prevention strategies implemented locally as some
scholars had already shown in QM in the past. This is coherent with Ullberg’s concept of
‘memory scape’ [112–114]. In the field of social sciences, this refers to the dynamic config-
uration of memory in disasters, constituted by memories, forgetfulness, and reminis-
cences that are expressed through multiple ways, ranging from everyday practices, public
documents, rituals, monuments, signs, and all kinds of physical signs that became part of
disaster landscapes. As is argued by Masi [115], this concept is a valuable input for recog-
nition and understanding of social behaviors, which are not only gravitating as demands
of explicit statements of public interventions, but essential when formulating public poli-
cies on risk management and disaster mitigation.
The geo-social map, as an experimental and exploratory tool for mapping the envi-
ronmental interactions in the Macul basin (QM), is an exercise of making the aforemen-
tioned territory complexities visible and useful for the community. Even the appropriate
consideration of different risk perceptions, social, political, and institutional aspects are
essential for successful risk management [116]. There is still limited experience on how
technical risk analysis can be applied in areas with scarce or absent data as it happens in
developing countries of Latin America, and also how it can be effectively combined with
community-based risk management approaches [117]. As a result of a transdisciplinary
approach for landslides analysis and prevention, the geo-social map through a TDA ap-
proach functions as a primary tool to understand the complex geo-social characteristics of
flow-type landslides and to inspire new modes of making hazard assessments in the fu-
ture hand in hand with communities affected by landslides.
As Takeuchi et al. [118] and other scholars have shown, TDA practices have not been
widely exercised both in discipline and in actions. Even there are few examples world-
wide that apply this approach, one of the main differences between this research and oth-
ers carried out is the attempt of co-production of knowledge connecting epistemologically
different disciplines and actors to create holistic approaches using concepts and methods
originally created in other disciplines, to relate, integrate, bring together, synthetize, and
merge them [119]. Most examples of TDA research emerge from physical, earth sciences,
and engineering fields [24,35], and are often applied in a top-down manner [117].
The TDA approach of the Geo-Social Model seeks to fill this gap through the integra-
tion of epistemologically different disciplines—geology, social sciences, humanities—and
the rescue of community-based resources. This is new, since TDA research carried out
worldwide and in Latina America has its spotlight on science and technology stakeholders

Sustainability 2021, 13, 2501 37 of 44
[35] or national policy makers capabilities [120,121] in a general top-down manner. De-
spite this contribution, one of the main limitations of the research is the experimental and
exploratory character of the mapping, and further research must be done in order to ad-
vance in the inclusion of geo-social features in landslides analysis and future hazard maps.
6. Conclusions
We developed what we labeled the Geo-Social Model to understand the interactions
between geological processes, built interventions, and socio-cultural conditions in the for-
mation and consequences of the 1993 landslide in Quebrada de Macul, Santiago. As an
exploratory tool, this methodology brings together insights from the earth, social, plan-
ning, and engineering sciences to better understand and prevent socio-natural hazards in
a process in which the community is not only the final recipient of the results, but the
main actor defining the research questions, aims, and methods. While our exploration is
place-dependent, we claim that as a methodology the Geo-Social Model can be adapted
to other territories and communities to advance in a more integrated research in land-
slides.
As a way of conclusion, we want to discuss three main challenges of landslide anal-
ysis and prevention that arise from our research process. First, flow-type landslides—par-
ticularly in urban contexts—are often the result of anthropogenic disruptions of natural
balances and systems. These interventions, in turn, are the effect of long histories of ur-
banization, infrastructuring, and occupation that, while exceeding the memory of current
inhabitants, are passed intergenerationally and registered in the material and cultural tra-
jectories of the community. If the so-called Anthropocene has been coined to call into at-
tention the co-production of the geological and the social, then research into and interven-
tion upon urban landslides in the Anthropocene has to account for the histories (and sto-
ries) of communities about the geological modifications of their environment.
Second, transdisciplinary approaches are critical for sustaining robust and politically.
effective landslide risk prevention plans. What we learned in Quebrada de Macul is that
this entails a re-accommodation of disciplinary identities. While earth scientists are re-
quired to integrate forms of evidence and narration coming from social sciences and the
humanities that do not fit easily into ‘scientific’ accounts, social scientists have to engage
with community demands, which usually revolve around ‘hard’ data about past and fu-
ture events. Both earth and social scientists have to adapt their theories and methodolo-
gies to policy-oriented and often politically charged goals. Without the needed flexibility
to meet these requirements, transdisciplinarity risks being mere tokenism, a sexy concept
devoid from its epistemological and political implications.
Finally, inter- and trans-disciplinary approaches to landslide risk prevention need to
be integrated into municipal-level planning. Without understanding the compound na-
ture of landslides, and devising plans accordingly, landslides in Chile and elsewhere will
continue to affect millions of people. In the case of the Global South, the lack of resources
at the local level requires the implementation of ad-hoc programs at the state or federal
level to channel professional and technological resources to municipalities, districts, or
any other territorial subdivision. Fundamentally, it requires the empowerment of local com-
munities to secure their substantial participation in landslide risk prevention plans: While
governments often celebrate participation as arenas of encounter between communities
and experts, they often forget that the first step is to create the conditions for community
participation by restituting their political and territorial control.

Sustainability 2021, 13, 2501 38 of 44
Author Contributions: Conceptualization, M.T. and V.A.; methodology, F.R. and V.A.; software,
F.R.; validation, F.R. and V.A.; formal analysis, F.R. and V.A.; investigation, V.A., L.J., and F.R.;
resources, V.A., F.R., and L.J.; data curation, F.A. and V.A.; writing—original draft preparation,
V.A., F.R., and M.T.; writing—review and editing, V.A., F.R., and M.T.; visualization, F.R.; super-
vision, M.T.; project administration, CIGIDEN; funding acquisition, CIGIDEN. All authors have
read and agreed to the published version of the manuscript.
Funding: This research was funded by CIGIDEN (Center for Integrated Research on Disaster Risk
Management) N° 15110017 FONDAP 2011, and FONDECYT N° 1190528.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available on request from the
corresponding author.
Acknowledgments: We thank the generosity of our collaborators and territorial organizations that
actively work on the study area: Volunteer Forestry Brigade Alto La Florida (BEAF), National For-
estry Corporation (CONAF), Defense Movement for access to Water, Land and the Protection of the
Environment (MODATIMA), Alluvion Territorial Assembly (ATA), Intercultural Center Quebrada
de Macul (CIQMA), Neighborhood Council “El Esfuerzo”, Exclusion Zone leaderships, MAPUCHE
community of Quebrada de Macul and the inhabitants of “Toma Dignidad”. We also appreciate the
technical assistance of Fernando Candia, the comments made by the geologist Matías Clunes and
the sociologist Ricardo Rivas while we were carrying out the research; the dialogues established
with foundation Proyecta Memoria -particularly with his director Víctor Orellana and the executive
director Patricio Mora- and with Patricia Díaz, the creator and director of the web project “Disaster
Archive”. Finally, to CIGIDEN especially to L4 “Disaster culture and risk governance” and L1 “Solid
Earth Process Threats”.
Conflicts of Interest: The authors declare no conflict of interest and the funders had no role in the
design of the study; in the collection, analyses, or interpretation of data; in the writing of the manu-
script, or in the decision to publish the results.

Sustainability 2021, 13, 2501 39 of 44
Appendix A
Figure A1. Map of classification by area of the hydrographic basin (km
2
), in the eastern part of the city of Santiago
(Chile).
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