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Moraine-dammed lake failures in Patagonia and assessment of outburst susceptibility in the Baker Basin

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Glacier retreat since the Little Ice Age has resulted in the development or expansion of hundreds of glacial lakes in Patagonia. Some of these lakes have produced large (g‰¥ 106 m3) Glacial Lake Outburst Floods (GLOFs) damaging inhabited areas. GLOF hazard studies in Patagonia have been mainly based on the analysis of short-term series (g‰Currency sign 50 years) of flood data and until now no attempt has been made to identify the relative susceptibility of lakes to failure. Power schemes and associated infrastructure are planned for Patagonian basins that have historically been affected by GLOFs, and we now require a thorough understanding of the characteristics of dangerous lakes in order to assist with hazard assessment and planning. In this paper, the conditioning factors of 16 outbursts from moraine-dammed lakes in Patagonia were analysed. These data were used to develop a classification scheme designed to assess outburst susceptibility, based on image classification techniques, flow routine algorithms and the Analytical Hierarchy Process. This scheme was applied to the Baker Basin, Chile, where at least seven moraine-dammed lakes have failed in historic time. We identified 386 moraine-dammed lakes in the Baker Basin of which 28 were classified with high or very high outburst susceptibility. Commonly, lakes with high outburst susceptibility are in contact with glaciers and have moderate (> 8°) to steep (> 15°) dam outlet slopes, akin to failed lakes in Patagonia. The proposed classification scheme is suitable for first-order GLOF hazard assessments in this region. However, rapidly changing glaciers in Patagonia make detailed analysis and monitoring of hazardous lakes and glaciated areas upstream from inhabited areas or critical infrastructure necessary, in order to better prepare for hazards emerging from an evolving cryosphere.
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Nat. Hazards Earth Syst. Sci., 14, 3243–3259, 2014
www.nat-hazards-earth-syst-sci.net/14/3243/2014/
doi:10.5194/nhess-14-3243-2014
© Author(s) 2014. CC Attribution 3.0 License.
Moraine-dammed lake failures in Patagonia and assessment
of outburst susceptibility in the Baker Basin
P. Iribarren Anacona1, K.P. Norton1, and A. Mackintosh1,2
1School of Geography Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand
2Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand
Correspondence to: P. Iribarren Anacona (pablo.iribarren@vuw.ac.nz)
Received: 11 July 2014 – Published in Nat. Hazards Earth Syst. Sci. Discuss.: 29 July 2014
Revised: 15 October 2014 – Accepted: 19 October 2014 – Published: 5 December 2014
Abstract. Glacier retreat since the Little Ice Age has re-
sulted in the development or expansion of hundreds of glacial
lakes in Patagonia. Some of these lakes have produced large
(106m3) Glacial Lake Outburst Floods (GLOFs) damag-
ing inhabited areas. GLOF hazard studies in Patagonia have
been mainly based on the analysis of short-term series (50
years) of flood data and until now no attempt has been made
to identify the relative susceptibility of lakes to failure. Power
schemes and associated infrastructure are planned for Patag-
onian basins that have historically been affected by GLOFs,
and we now require a thorough understanding of the char-
acteristics of dangerous lakes in order to assist with haz-
ard assessment and planning. In this paper, the condition-
ing factors of 16 outbursts from moraine-dammed lakes in
Patagonia were analysed. These data were used to develop
a classification scheme designed to assess outburst suscep-
tibility, based on image classification techniques, flow rou-
tine algorithms and the Analytical Hierarchy Process. This
scheme was applied to the Baker Basin, Chile, where at least
seven moraine-dammed lakes have failed in historic time.
We identified 386 moraine-dammed lakes in the Baker Basin
of which 28 were classified with high or very high outburst
susceptibility. Commonly, lakes with high outburst suscepti-
bility are in contact with glaciers and have moderate (>8)
to steep (>15) dam outlet slopes, akin to failed lakes in
Patagonia. The proposed classification scheme is suitable for
first-order GLOF hazard assessments in this region. How-
ever, rapidly changing glaciers in Patagonia make detailed
analysis and monitoring of hazardous lakes and glaciated ar-
eas upstream from inhabited areas or critical infrastructure
necessary, in order to better prepare for hazards emerging
from an evolving cryosphere.
1 Introduction
Amongst the most frequent and damaging processes related
to glaciers are Glacial Lake Outburst Floods (GLOFs). The
failure of glacial lakes can release millions of cubic me-
tres of water in a short time (minutes to days) and pro-
duce floods with high peak discharges (104m3s1) and re-
markable erosive and transport capacity (Costa and Schuster,
1988; Breien et al., 2008). GLOFs can occur through differ-
ent mechanisms. Moraine-dammed lakes commonly fail due
to overtopping and the progressive enlargement of a breach
in the dam. Rainfall, meltwater and waves produced by mass
movements, ice avalanches or calving often trigger the over-
flow and subsequent moraine-dam failures (Costa and Schus-
ter, 1988; Emmer and Cochachin, 2013). Piping after earth-
quakes, the mechanical failure of ice-cored moraines and
flow waves from upstream lake failures have also been re-
lated to GLOFs (Lliboutry et al., 1977; Buchroithner et al.,
1982).
In the Himalayas, European Alps and the Andes GLOFs
have affected mountain communities for centuries, result-
ing in thousands of casualties (Hewitt, 1982; Grove, 1987;
Reynolds, 1998). However, the generation of new glacial
lakes as a consequence of glacier retreat, and the eco-
nomic exploitation of previously uninhabited valleys make
the emergence of new endangered areas likely. For example,
in Chilean Patagonia, hydroelectric generation plants are be-
ing planned in areas that have historically been influenced by
GLOFs (Dussaillant et al., 2009; Vince, 2010). Thus, there is
now an urgent need to better understand and assess the GLOF
hazard in these regions where detailed analyses are lacking.
Published by Copernicus Publications on behalf of the European Geosciences Union.
3244 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
Figure 1. (a) Geographical setting and name (unofficial) of failed moraine-dammed lakes in Patagonia used to develop a GLOF susceptibility
classification scheme. (b) Failed dams are located in zones with annual precipitation ranging from 500 to 2000 mm and where mean monthly
temperature in winter is generally above 0C. (c) Note the decrease in the number and magnitude of earthquakes south of the 46S and
the high frequency of shallow earthquakes (hypocentre <30km). Climate data extracted from Hijmans et al. (2005) and from the National
Climatic Data Center (http://www.ncdc.noaa.gov). Seismic data (period 1973–2012) retrieved from the Northern California Earthquake Data
Center (http://www.ncedc.org/anss/catalog-search.html).
A first step towards the analysis of GLOF hazards is the
identification of glacier lakes. Remote sensing methods (e.g.
image classification techniques) are especially suitable for
this task allowing rapid analysis of large areas (hundreds
of square kilometres) in an inexpensive way (Huggel et al.,
2002; Kääb et al., 2005). Using these methods, hazardous
lakes can be identified, and subsequently, if they are found
to pose a potential risk to lives or infrastructure, more de-
tailed local studies (e.g. GLOF modelling) might be devel-
oped (Mergili and Schneider, 2011) (e.g. Bajracharya et al.,
2007; Worni et al., 2012). Hazardous lakes are identified
by comparing lake characteristics (e.g. dam geometry and
potential for ice avalanche impacts entering the lake) with
those of failed lakes and their surroundings (McKillop and
Clague, 2007; Bolch et al., 2011; Wang et al., 2011; Emmer
and Vilímek, 2013). In Patagonia, data about failed moraine-
dammed lakes have not been systematically analysed and the
contributing factors of most of the failed moraine-dammed
lakes are unknown.
Since the beginning of the 20th century, at least 16
moraine-dammed lakes have failed in Patagonia (Iribarren
Anacona et al., 2014). Seven of these lakes are located in
the Baker Basin where major hydroelectric generation plants
are planned. One of these GLOFs (Laguna del Cerro Largo)
is probably the largest outburst of a moraine-dammed lake
(in terms of water volume released, 229×106m3)reported
worldwide (Hauser, 1993; Clague and Evans, 2000). In the
Baker Basin GLOFs have destroyed houses, forced the relo-
cation of a village and have damaged inhabitant’s livelihoods
(Iribarren Anacona et al., 2014). Furthermore, a flood wave
with GLOF characteristics killed three people boating in the
Baker River in January 1977 (El Diario de Aysén, 1977a, b).
This makes the Baker Basin an important location to study
the GLOF hazards.
In spite of the damage and the increasing frequency of
GLOFs in Patagonia, and the Baker Basin, GLOFs haz-
ards studies have been limited and based mainly on sta-
tistical analysis of short series (<50 years) of flood data
(HidroAysén, 2008; Vince, 2010). The relative susceptibil-
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P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3245
Figure 2. Location of moraine-dammed lakes and settlements in the
Baker Basin.
ity to failure of moraine-dammed lakes in the Baker Basin is
currently unknown as well as the extent to which these lakes
pose a threat to infrastructure or human life.
In summary, GLOFs might pose a significant hazard to
lives and newly developing infrastructure in Patagonia, but
several questions remain unanswered concerning their past
behaviour. Thecurrent status of moraine-dammed lakes, one
of the prime sources of GLOFs, remains uncertain. We aim to
analyse previously failed moraine-dammed lakes in Patago-
nia to identify the conditioning factors that led to failure, and
to use these data to identify the moraine-dammed lakes most
susceptible to future failure in the Baker Basin.
1.1 Setting
Patagonia is a region located in the southernmost part of
South America (40S) in the territories of Chile and Ar-
gentina (Fig. 1). This region hosts some of the largest temper-
ate ice masses on Earth (Harrison, 2011). However, glaciers
in Patagonia have suffered significantlosses in mass since the
maximum Little Ice Age (LIA) expansion (between the 16th
and 19th centuries) (Masiokas et al., 2009a), resulting in the
formation or growth of several ice-, bedrock- and moraine-
dammed lakes (Loriaux and Casassa, 2013). North-facing,
land-terminating glaciers with surfaces <5km2have shown
the fastest retreat in the region (Davies and Glasser, 2012).
The Baker Basin is located between 46 and 48S, in the
eastern side of North Patagonian Icefield (NPI) and has a sur-
face area of about 20 500 km2of which ca. 1940km2are cov-
ered by ice (Fig. 2). Climate varies from arid continental, in
the East (precipitation ca. 200mm year1) to maritime hy-
perhumid on the west side of the Andean main divide (pre-
cipitation ca. 2000 mm year1). Seismicity in the Baker basin
is low. Seismic activity has been concentrated in the north as-
sociated with Hudson Volcano eruptions; however seismic-
ity decreases south of 46S (Barrientos, 2007) and no recent
seismicity (from 1973 onwards) has been recorded in the rest
of the basin. The Baker Basin is sparsely populated, mainly
by low-density rural settlements. The number of tourists that
visit the region is low (Muñoz et al., 2006). The basin hosts
pristine rainforest, lakes and glaciers. Hundreds of glacier
lakes exist in the Baker Basin where major hydroelectric
schemes are planned. This makes the basin an ideal site to
study the hazard posed by glacier lakes in Patagonia.
2 Data and methods
Data from historical outburst floods in Patagonia were used
to develop an outburst susceptibility classification scheme
which was applied in the Baker Basin. This section details
the data used and procedures followed to (a) characterize the
failed moraine dams in Patagonia (b) to select, measure and
weight the outburst susceptibility factors and to (c) define the
outburst susceptibility classes (Fig. 3).
2.1 Data
Morphometric characteristics of dams, glaciers and lake
catchments were extracted from Landsat TM and ETM+im-
ages. Both Landsat TM and ETM+images have a spatial
resolution of 30m (15 m for the ETM+panchromatic band)
and were acquired from http://glovis.usgs.gov/. Topographic
data were derived from the Advanced Spaceborne Thermal
Emission and Reflection Radiometer Global Digital Eleva-
tion Model (ASTER GDEM V2). The spatial resolution of
the ASTER GDEM V2 is 1 arcsecond (approximately 30m)
and the DEM has a vertical accuracy of 17m (Tachikawa et
al., 2011).
2.2 Characterization of failed moraine-dammed lakes
in Patagonia
The 16 moraine-dammed lakes that failed in historic time in
Patagonia were mapped manually using Landsat images. In
the oldest events (before 1985) the lake area and glacier ex-
tent prior to the outbursts were reconstructed using historical
documents or geomorphic features (e.g. trimlines and lake
shorelines). Morphometric parameters in these cases are less
accurate than in GLOFs which occurred after 1985 but they
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3246 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
Table 1. Data of 16 GLOFs in Patagonia and characteristics of the moraine-dammed lakes and their surroundings prior to the failure.
Site Date Lake area (km2) Ov (m3×106) Pd (m3s1) Pl (km) H/L () Dh (m) Dos () Glc Ias Mms Plg
Before After
1. Gl. Frías 1942–1953 0.01 0 0.06 81 10? 35 Y(b) Y Y N
2. Gl. Ventisquero Negro 21 May 2009 0.55 0.32 4.36 1301 7.1 1.1 30 18 Y N Y Y
3. Río Lacaya 2000–2001 0.33 0.15 3.14 1048 21.5 3 10? 9 Y Y Y N
4. Monte Erasmo 1985–2000 0.71 0.69 0.16 150 6.0 2.1 10? 8 Y N Y Y
5. Estero El Blanco 2000–2003 0.12 0.04 1.05 511 5.4 5.1 10? 11 N N Y N
6. Río Engaño 11 Mar 1977 1.15 0.81 7.36 1839 6.5 2.1 50 24 Y Y Y Y
7. Estero El Pedregoso 1985–1987 0.12 0.09 0.28 214 5.0 8.4 4 Y(c) N Y Y
8. Río Los Leones 2000 0.02 0 0.16 150 2.3 7.4 40 22 N N Y N
9. Río Viviano 1987–1998 0.02 0.01 0.06 81 2.3 7.3 15 26 N Y Y N
10. Cerro Largo 16 Mar 1989 1.82 0.98 24.73 4092 13.0 1.1 160 26 Y Y Y N
11. Estero Las Lenguas 1987–1998 0.67 0.44 4.36 1301 23.8 1.3 110 21 Y Y Y N
12. Gl. Piedras Blancas 16 Dec 1913 0.21 4.5 2.6 80 21 Y Y Y Y
13. Seno Mayo 2001–2003 0.07 0.03 0.41 277 2.3 19 10? 8 Y N Y Y
14. Gl. Olvidado 2003 0.53 5.8 2.6 20 10 Y N Y Y
15. Última Esperanza 1999–2006 0.09 0.08 0.06 81 10.6 4.0 10? 5 Y(c) Y Y Y
16. Peninsula de las Montañas 2005–2006 0.07 0.06 0.06 81 2.0 8.4 10? 20 Y N Y Y
Abbreviations: Outburst volume (Ov), Peak discharge (Pd), Path length (Pl), Angle of reach (H/L), Dam height (Dh), Dam outlet slope (Dos), Glacier lake contact (Glc), Ice avalanche susceptibility (Ias), Mass movement
susceptibility (Mms) and Potential lake growth (Plg). Ov was calculated using the lake area lost after the GLOFs in the lake’svolume formula. (B) Data inferred from the position of Glacier Frías front in 1935-1938 (see Villalba
et al., 1990). (C) Lake in contact with a debris-covered glacier. GLOF data sourced from Iribarren Anacona et al. (2014) and references therein.
Figure 3. Flow chart of procedures followed to classify lake out-
burst susceptibility in the Baker Basin.
still provide an approximation of the lake and glacier condi-
tions prior to the dam failures (Table 1). The basin and glacier
topography were extracted automatically from the ASTER
GDEM using standard spatial analysis tools (see Reuter and
Nelson, 2008).
The GLOF paths were mapped on Landsat images and,
when available, high-resolution satellite images (5 m) from
Google Earth. GLOF angle of reach was measured along the
flow path, from the dam breach to the lowest area of stripped
vegetation or sediment deposition. Thus, path lengths may
be underestimated in the oldest events due to vegetation re-
Figure 4. Empirical curves showing the relationship between area
and volume of glacial lakes. The green curve was obtained from
38 data of lake area and volume of 25 moraine-dammed lakes
worldwide. Note that the lake volume does not increase propor-
tionally with an increase in the lake area and that the major diver-
gence between curves occurs on the largest lakes where fewer data
are available. Data extracted from O’Connor et al. (2001), Huggel
et al. (2002), Allen et al. (2009), Rivas (2012) and Loriaux and
Casassa (2013).
growth. The dam height and outlet slope were derived from
topographic profiles drawn over the ASTER GDEM (30m of
spatial resolution) on undisturbed sections of the dam near
the original lake outlet. Breaks in the topographic profile
were not straightforward to map in the case of small dams
(probably 10m in height), making it difficult to estimate
the dam geometry.
Lake volume and outburst peak discharges were calculated
using empirical formulae. Several formulae exist that relate
lake area and volume. Formulations by Huggel et al. (2002)
and Loriaux and Casassa (2013) are based on data of ice- and
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P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3247
moraine-dammed lakes, whereas the O’Connor et al. (2001)
formula is based on a small number of moraine-dammed
lakes. Ice- and moraine-dammed lakes often have different
geometries (McKillop and Clague, 2007) and therefore dif-
ferent volumes. Thus, we collected data from literature of a
large number of moraine dammed lakes worldwide (38 mea-
surements of lake area and volume from 25 lakes; Fig. 4)
and derived the following empirical formula to calculate lake
volume:
V=31.249A1.3399,
where Vis the lake volume in m3×106and Ais the lake
area in km2.
We compared the measured volume of 38 data of moraine
dammed lakes with the volume estimated with the derived
empirical formula. The mean error of the volume estimates
was ±71%.
The peak discharge was calculated using the following for-
mula proposed by Walder and O’Connor (1997):
Q=0.054V0.66,
where Vis the lake volume in m3.
Outburst parameters estimated by regression-based meth-
ods have large uncertainty. Dam breach peak discharge esti-
mates can have uncertainties of up to ±1 order of magnitude
(Wahl, 2004).
2.3 Selection of outburst susceptibility factors
Lakes dammed by temperate glaciers may be considered in-
herently unstable since ice-dam characteristics (e.g. glacier
thickness, crevassing and bed adhesion) are subject to fre-
quent changes, affecting the ice-conduit dynamics (Tweed
and Russell, 1999). Consequently, we considered all the ice-
dammed lakes as hazardous. Thus, we centred our analy-
sis on selecting variables to identify moraine-dammed lakes
susceptible to failure. Several variables have been used to
identify hazardous moraine-dammed lakes (see Emmer and
Vilímek’s, 2013, review paper). The dam geometry (e.g.
width-to-height ratio, flank steepness and dam freeboard)
and internal structure (e.g. presence of ice and particle size
distribution) are probably the most important conditioning
factors of outburst floods (Richardson and Reynolds, 2000a).
However, most dam characteristics can only be measured ac-
curately in the field or by using high-resolution satellite im-
ages or DEMs. We chose six characteristics of lakes, dams
and their surroundings that can be measured and modelled
using medium-resolution satellite images and DEMs. These
variables comprise outburst conditioning and triggering fac-
tors and also give an idea of the outburst damaging potential.
Due to the low spatial and temporal resolution of meteorolog-
ical data in Patagonia, extreme meteorological events were
not included in the analysis. The selected outburst factors are
described below.
Figure5. (a)Results of ice avalanche modelling and automatic clas-
sification of glaciers. (b) Examples of lake outlet slope measure-
ments.
2.3.1 Lake area
Lake dimensions have been directly related to outburst vol-
ume, peak discharge and the flood damage potential (Costa
and Schuster, 1988). Accordingly, larger lakes are consid-
ered to be more hazardous than small lakes. Furthermore,
lakes with larger areas are generally deeper (see e.g. Diaz
et al., 2007 database), and may exert higher hydrostatic pres-
sures over the dams making them more susceptible to failure
(Richardson and Reynolds, 2000b). Larger lakes also have a
greater surface area potentially exposed to mass movement
and ice avalanche impacts, increasing their outburst suscep-
tibility.
2.3.2 Glacier–lake contact
Lakes in contact with glaciers can be affected by calving and
the sudden floating of dead ice. Both mechanisms can pro-
duce waves capable of overtopping dams starting a breach-
ing process and subsequent dam failure (Richardson and
Reynolds, 2000a). Icebergs also can block the lake outlet,
raising the water level potentially overtopping and breaching
the dam. Thus, lakes in contact with glaciers are considered
more hazardous than lakes detached from the glacier snout.
2.3.3 Slope of glacier terminus
A glacier with a low-angle terminus can be an indicator of
a negative mass balance. Consequently, lakes in contact with
flat glacier fronts (slopes less than 5) are likely to grow as
a consequence of glacier retreat (Frey et al., 2010a). Lakes
that are expected to grow are more hazardous than lakes
which are expected to remain stable or shrink (examples of
minor moraine dammed lake area reduction, not related to
GLOFs, have been observed in Patagonia; see Fig. 5d in Lo-
riaux and Casassa, 2013), since the potential area exposed
to mass movements or ice avalanches may increase and the
dams may be subject to higher hydrostatic pressures.
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3248 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
2.3.4 Lake outlet slope
Steep outlets can be more easily enlarged than low-gradient
outlets if an increase in the lake discharge occurs. Progres-
sive erosion can widen and deepen the outlet leading to
lake drainage. Consequently, dams with steep outlets are
more susceptible to failure (O’Connor et al., 2001). Further-
more, high dams which produce outbursts with high peak
discharges (Walder and O’Connor, 1997) usually have steep
outlets (see Table 1).
2.3.5 Glacier steepness above lake
Steep (25) temperate glaciers are a common source of
ice avalanches (Alean, 1985). Ice avalanches impacting lakes
can generate impulse waves capable of overtopping dams
starting catastrophic lake drainage. The likelihood of an ice
avalanche impacting a lake depends on the distance, slope
and roughness of the terrain between the glacier and the wa-
ter body. Ice avalanches are the most common cause of out-
burst floods in the Himalayas (Wang et al., 2011) and have
also been reported in the Tropical Andes (Lliboutry et al.,
1977).
2.3.6 Steepness of slopes above lake
Steep unvegetated slopes are a common source of mass
movements (Peduzzi, 2010) and can be indicators of high
geomorphic activity. Large and high-velocity landslides can
generate impulse waves of hundreds of metres of run-up that
can easily overtop dams starting progressive erosion and lake
drainage (Walder et al., 2003). Lakes can also be suddenly
drained by large waves without a dam-breaching process
(Clague and Evans, 2000). Mass movement impacts have
been related to outburst floods in Patagonia and other An-
dean regions (Hubbard et al., 2005; Harrison et al., 2006).
2.4 Measuring and modelling of selected factors
2.4.1 Glacier and lakes delimitation
Glaciers and lakes were delimited using multispectral clas-
sification techniques that exploit the maximum reflectance
difference of a surface (i.e. glaciers and lakes) in different
spectral channels to identify the desired object (Huggel et al.,
2002; Paul et al., 2002). Thresholded band ratios have been
successfully used in glacier inventories (e.g. Andreassen et
al., 2008; Svoboda and Paul, 2009). We mapped glaciers via
band rationing of the near-infrared and mid-infrared bands
of Landsat images in reflectance values (i.e. pixel values not
converted to radiance; Paul et al., 2002). The thresholds val-
ues to identify glaciers (bare ice) were defined comparing
visually the band ratio image with false composite Landsat
images (Table 2). Debris-covered glaciers were drawn man-
ually.
Lakes in the Baker Basin were mapped using the Normal-
ized Difference Water Index (NDWI) of Huggel (2002) ob-
tained from the following equation:
NDWI =(Near-Infrared BandBlue Band)
/(Near-Infrared Band+Blue Band).
The NDWI was applied on Landsat images in Digital Num-
bers. A cast-shadow mask was used to eliminate shadowy
areas mistakenly classified as lakes (see Huggel et al., 2002).
A median filter of 3×3 kernels was applied to smooth
the glacier and lake surfaces incorporating or eliminating iso-
lated pixels in the classified image (Paul et al., 2002). Mis-
classified lakes in shadowy areas and debris-covered glaciers
were corrected manually. The error in lake and glacier de-
limitation is estimated to be one pixel (i.e. ±30 m) although it
can be larger in shadowy areas. The lake inventory was devel-
oped using images from the years 2000 and 2002. However,
Landsat images of the years 2012 and 2013 also were anal-
ysed to manually incorporate recently formed lakes in the
inventory and to assess the glacier–lake contact status. Only
the area of lakes in contact with glaciers was determined us-
ing 2012–2013 images since the area of other lakes probably
remained stable (see Loriaux and Casassa, 2013). The 2012–
2013 images were not used as base for the entire inventory
since about 20% of the data in each Landsat 7 image were
lost after the failure of the scan-line corrector in May 2003
(USGS et al., 2003). Google Earth images were used to clas-
sify the dams (i.e. moraine, bedrock or ice dams). Only lakes
located in valleys glaciated during the LIA were included in
the analysis since lakes situated far from the LIA expansion
(including very large moraine-dammed lakes such as Gen-
eral Carrera and small lakes dammed by bedrock) were con-
sidered to be stable. Published geomorphological maps were
used to identify the glacier extent during LIA (Glasser et al.,
2011; Glasser and Jansson, 2008), which was also inferred
from trimlines and terminal moraines.
2.4.2 Slope steepness above lake and mass movement
modelling
Mass movement paths were mapped using the Modified Sin-
gle Flow Direction (MSF) model of Huggel et al. (2003). The
MSF simulates the trajectory of mass movements from the
source area following the steepest descent with a maximum
deviation of 45. The mass movement stops (i.e. the end of
the path) when it reaches a predetermined ending condition
generally set as the angle of reach (i.e. the angle of the line
connecting the starting and the ending zone of a mass move-
ment; Hsu, 1975) (see Huggel et al., 2003 and Gruber et al.,
2008 for model details).
Published data of the angle of reach of mass movements
and typical angles of detachment zones were used as input
to model the flow paths. The angle of reach and the slope of
the starting zone of rock falls, debris flows and other com-
plex mass movements vary locally according to the geol-
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P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3249
Table 2. Satellite images and threshold used to identify glaciers, lakes and vegetation.
Glacier band Lakes NDWI Vegetation NDVI
Sensor Image date Path/row ratio threshold threshold threshold
Landsat ETM+
8 Mar 2000 232/092 3 0.5 0.1
8 Feb 2013 232/092
18 Feb 2002 231/093 2.5 0.45 0.1
18 Feb 2002 231/092 1.5 0.45 –
8 Mar 2000 232/093 3 0.5 –
22 Feb 2012 232/093
Table 3. Pairwise comparison of outburst predictor variables and consistency ratio.
Glacier–lake Lake Glacier steepness Slope steepness Slope of Lake outlet
Matrix contact area above lake above lake glacier terminus slope
Glacier–lake contact 1 2 2 2 3 1
Lake area 1/2 1 1/2 2 2 1/3
Glacier steepness above lake 1/2 2 1 3 3 1/2
Slope steepness above lake 1/2 1/2 1/3 1 2 1/3
Slope of glacier terminus 1/3 1/2 1/3 1/2 1 1/5
Lake outlet slope 1 3 2 3 5 1
Consistency ratio: 0.026
Factor intensity: 1: Equal importance; 3: Moderate prevalence of one over another; 5: Strong or essential prevalence; 7: Very strong or demonstrated prevalence; 9:
Extremely high prevalence; 2, 4, 6 and 8: express intermediate values (after Saaty and Vargas 2001).
ogy, terrain roughness and vegetation coverage. Steep un-
vegetated slopes may indicate high geomorphic activity and
can be associated with loose, readily erodible material. Thus,
we assume potential starting zones for all mass movements
are unvegetated or sparsely vegetated slopes 30. We have
not distinguished between solid bedrock slopes and non-
cohesive slopes since this task can only be accurately ac-
complished by photo interpretation or fieldwork, which are
costly or time consuming, and consequently not suited to our
preliminary regional analysis.
Vegetation was mapped using the Normalized Vegetation
Index (NDVI) calculated using the following equation:
NDVI =(Near-Infrared BandRed Band)
/(Near-Infrared Band+Red Band).
The angle of reach of mass movements was considered sim-
ilar to that of rock avalanches (about 15; see Nicoletti and
Sorriso-Valvo, 1991) which are the events most likely to start
catastrophic lake drainages.
2.4.3 Glacier steepness above lake and ice avalanche
modelling
The ice avalanche paths were also delineated using the MSF
model based on empirical data of ice avalanches source
and angle of reach (Fig. 5). According to Alean (1985)
ice avalanches commonly start at slopes 25in temperate
glaciers (such as Patagonian glaciers) and have an angle of
reach of 17(data derived from about 100 ice avalanches
mostly from the European Alps). Thus, we mapped glacier
surfaces with slopes 25and used these areas as ice
avalanche detachment zones. The stopping condition in the
MSF model was set at an angle of reach of 17.
2.4.4 Lake outlet slope measurement
The lake outlet and the outlet slope were identified and mea-
sured automatically following a series of GIS procedures.
First, we identified the lake outlet as the point with maxi-
mum flow accumulation in the lake (see Gruber and Peck-
ham, 2008). From this point the steepest descent path 200
metres downstream (with a maximum deviation of 45) was
calculated using the Path Distance tool of ArcGIS. We as-
sumed that moraine-dam widths are less than 200m. Dam
widths of the largest failed lakes in Patagonia are 300m.
However, we used a smaller value since most of the moraine-
dammed lakes in the Baker Basin are small and this value
(200m) does not significantly affect the average slope of
larger dams. Finally, the mean slope of the steepest descent
path was calculated.
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3250 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
Table 4. Weight of variables associated with moraine-dammed lake failures.
Variable weight
Lake outlet Glacier–lake Glacier steepness Lake area Stability of slopes Slope of
slope contact above lake above lakeglacier terminus
30 25 18 12 9 6
Classes weight
151 Yes 1 251>0.5km21 Yes 1 Yes 1
8and <150.75 No 0 <250>0.1 to 0.5km20.75 No 0 No 0
<80 0.01 to 0.1 km20.5
Mass movements are a common cause of outburst floods. However, we assigned to this variable a low weight because the slope steepness and vegetation cover only provide a rough idea of
potential detachment zones.
2.5 Weighting process
After analysing 16 GLOFs in Patagonia, the six conditioning
factors were weighted using the Analytical Hierarchy Pro-
cess (AHP) (Saaty, 1980). We chose this method since it al-
lows evaluation of the consistency of the subjective judge-
ments which is not accomplished by other qualitative or
semi-quantitative GLOF hazard approaches (see Emmer and
Vilímek, 2013, for a review). The AHP is a multicriteria
decision-making technique which allows estimation of the
relative significance of factors contributing to an event based
on pairwise comparison, expert judgment and the linear al-
gebra transformation of the comparison factors matrix (Ta-
ble 3). The aim of the pairwise comparison is to assess the
significance of one factor compared to another. Values from
1 to 9 can be assigned to each factor, where a value of 1
means that both factors have equal importance and a value of
9 means that a factor has an extreme prevalence over another.
The AHP method has been used in natural hazard assess-
ments by several authors (e.g. Ayalew et al., 2005; Lari et
al., 2009). The AHP also allows the evaluation of the consis-
tency of the judgements based on the estimation of the eigen-
value of the factors matrix. Generally only consistency ratios
<0.1 are considered acceptable (Satty, 1980). We assigned
the higher weights to the GLOF factors more frequently as-
sociated with GLOFs in Patagonia. After weighting the six
GLOF factors, each factor was subdivided into classes for
which we assigned weights (Table 4). The total GLOF sus-
ceptibility score for each lake was obtained by multiplying
the weight of the factor by the weight of the classes and then
adding up the six factor scores. The highest possible score is
100.
To define the outbursts susceptibility classes we applied
the outburst classification scheme to the failed lakes in Patag-
onia. Five categories that represent five relative scales of out-
burst susceptibility were defined (Fig. 6). Twelve (75%) of
the 16 recorded failed lakes in Patagonia had scores 65.
Thus, a score of 65 was used as threshold to classify lakes
with high outburst susceptibility.
Figure 6. Outburst susceptibility score of the 16 moraine-dammed
lakes failed in Patagonia. These data were used to define five out-
burst susceptibility classes.
3 Results
This section summarizes characteristics of moraine-dammed
lakes failed in Patagonia. The data provide insights to iden-
tify moraine-dammed lakes with high outburst susceptibility
in the region.
3.1 Characteristics of GLOFs, failed lakes and their
surroundings
3.1.1 GLOFs characteristics
Moraine-dammed lakes that failed in historic time in Patago-
nia had areas ranging from 0.01 to 1.82km2(Table 1). Four-
teen lakes experienced just a partial emptying; including the
largest lake (Laguna del Cerro Largo) which released an esti-
mated water volume of 229×106m3(Hauser, 2000). The
outburst paths (patches of stripped vegetation and/or debris
deposition visible in Landsat images) range from few kilo-
metres up to 27km in length and commonly are less than
100m wide. However, GLOFs probably reached farther ar-
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P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3251
Figure 7. Accumulated percentage of GLOF paths within different
angles of reach (H/L). Most path sections with H/L 10(where de-
bris flows often occur) are located at distances 3000 m from failed
lakes. Sections with H/L10(89 % of the total path lengths) of-
ten have diffusive and rapidly attenuating flows. H/L was measured
every 10m from 15 failed moraine-dammed lakes in Patagonia.
eas since vegetation recovery might conceal evidence of flow
after just a few years. This has been corroborated by eye-
witness’s accounts (interviews held by the authors with in-
habitants of Los Leones valley and Bahía Murta Village)
which indicate that floating debris (large trees) were trans-
ported during GLOFs to the river outlets, kilometres from
the preserved geomorphic evidence, clearly posing a risk for
inhabited areas. GLOF paths are dominated by steep slopes
up to five kilometres from the lakes (Fig. 7). These sections
of the GLOF paths favour the development of debris flows
and the transport of coarse material from failed dams. In the
lowest areas, patches of stripped vegetation and bank erosion
are common, although the flows attenuate due to wider val-
leys and lower slopes.
3.1.2 Dam characteristics
Outbursts have affected moraine dams with different geome-
tries. Drained lakes were dammed by both, steep moraine
arcs and relatively flat ground moraines. No relationship be-
tween moraine heights and failure was evident, although
higher dams (associated with larger lakes) resulted in GLOFs
with higher peaks discharges. The heights of the failed dams
vary from a few metres to up to 160m. In eight cases the
dams were small making it difficult to accurately estimate
their dimensions. However, they were probably 10m high.
Nine dams were vegetated at the time of failure and one of
them (Piedras Blancas) was covered by mature forest dat-
ing from the early 1600s (Masiokas et al., 2009b). Most of
the failed lakes had moderate to steep outlet slopes. The out-
let slope of 14 lakes was 8and 8 lakes had outlet slopes
5. The dam’s internal composition is known in just one
case. The Ventisquero Negro dam was composed of non-
cohesive coarse material (boulders and blocks) in a matrix of
Figure 8. Types of moraine dams failed in Patagonia; (a) lake
perched over moraine deposits (b) lake dammed by ground
moraines and partially by bedrock (c) lake dammed by a small crest-
shaped dam and (d) lake behind large and steep vegetated dam. Im-
ages sourced from Google Earth.
sand and gravel. This dam was vegetated and also presented
an ice-core at the time of failure (Worni et al., 2012). Estero
el Pedregoso Lake was dammed by (or was embedded in)
glaciofluvial deposits and was partially dammed by bedrock
(Fig. 8).
3.1.3 Characteristics of upstream catchments
Moraine-dammed lakes that produced outburst floods in
Patagonia were located in different settings. Thirteen lakes
were in contact with a glacier at the time of failure and in
at least three cases (Ventisquero Negro, Olvidado and Penín-
sula de las Montañas) glaciers exhibited rapid retreat before
the outburst floods (Fig. 9). For example, between 2000 and
2003 the Olvidado Glacier retreated 271m per year (Rivera
and Casassa, 2004) significantly increasing the lake surface
before the failure. Half of the lakes were located in areas
prone to ice avalanches. In fact, the upper-edge of Lacaya and
Las Lenguas lakes were at the toe of reconstituted glaciers,
clear indicators of high snow and ice avalanche activity
(Fig. 9). All of the lakes were surrounded by steep (25)
valley walls or moraines. Rock-falls, snow avalanches and
debris flows are common in this setting. However, a mass
movement was definitely identified as the cause of the dam
failure in just one case (see Harrison et al., 2006). In the other
cases (excluding Piedras Blancas and Frías outbursts) no ev-
idence of large mass movements (i.e. fresh landslide scars
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3252 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
Figure 9. Settings of moraine-dams failed in Patagonia; (a) lake
in the head of a catchment at the toe of a reconstituted glacier,
(b) growing lake in contact with a retreating glacier and (c) lake
distant from the glacier tongue. Note the steep slopes and glaciers
surrounding the lakes.
or deposits) in the lake’s surroundings were identified when
comparing images before and after the outburst floods.
3.1.4 Triggering factors
The triggering of only 3 of the 16 GLOFs is known. However,
these events exemplify the variety of factors that can cause
outburst floods. These factors include gravitational processes
and meteorological events. The outburst of the Calafate Lake
in the Río Los Leones Valley was caused by the impact of
a rock-fall into the lake. The rock-fall detached from a re-
cently deglaciated slope and completely covered the lake’s
area (Harrison et al., 2006) generating impact waves that
probably caused an almost instantaneous lake emptying. The
Río Engaño outburst was caused by a different gravitational
process. Reconnaissance flights carried out few days after the
Río Engaño outburst indicate that the lake was impacted by
glacier ice (this might correspond to an ice avalanche or calv-
ing) that probably caused waves which overtopped the dam
and started the lake drainage (El Diario de Aysén, 1977c).
The Ventisquero Negro outburst occurred after prolonged
(180mm of rain in 6 days) and intense (50 mm of rain in
the 48h prior the outburst) rainfall that possibly caused an
overflow and subsequent dam breach and failure (Worni et
al., 2012).
3.2 Glacial lakes in the Baker Basin
Overall, 480 glacial lakes with surfaces 0.01km2were
identified in the Baker Basin. Distinguishing between
bedrock and moraine-dammed lakes proved to be difficult.
All uncertain cases (<10%) were classified as moraine-
dammed lakes in order to evaluate their outburst suscepti-
bility. A preliminary classification indicated that 85 lakes are
dammed by bedrock and 386 (80%) lakes are dammed by
moraines. Only three lakes are dammed by glaciers. Two of
them are dammed by the Colonia Glacier, the Lake Cachet
2 (drained 10 times between 2008 and 2012) and a smaller
(0.35km2) unnamed lake located 10 km to the north. A fourth
ice-dammed lake (Laguna Bonita) emptied at least two times
between 2002 and 2008. However, glacier retreat since the
last outburst now impedes the lake refilling (Iribarren Ana-
cona et al., 2014). Of the 386 moraine-dammed lakes at least
seven have produced outburst floods.
3.2.1 Lake outburst susceptibility in the Baker Basin
According to our classification scheme, the majority of the
moraine-dammed lakes in the Baker Basin have low outburst
susceptibility. The lakes have low-gradient outlets, are dis-
connected from glaciers or are small (<0.1km2)(Fig. 10).
However, such lakes may still produce outburst floods as
they are subject to ice avalanches or mass movement im-
pacts. Seven moraine-dammed lakes are in the range of very
high outburst susceptibility and 21 lakes are in the range of
high outburst susceptibility (Fig. 6). A closer look of these
lakes, however, shows that the largest lakes are located in
flat valleys and have superficial drainage through large (sev-
eral metres) low-gradient outlets making a catastrophic lake
drainage unlikely. This is the case for example of the Fiero,
Laguna Soler and Cachet 1 lakes. While these lakes are ex-
posed to ice avalanches or mass movements, impact waves
may be attenuated after travelling long distances (Slinger-
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P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3253
Figure 10. (a) Characteristics of 16 failed moraine-dammed lakes
in Patagonia and (b) characteristics of 386 moraine-dammed lakes
in the Baker Basin.
land and Voight, 1979), reducing the outburst susceptibility.
Low-gradient outlets also limit the transformation of even-
tual outburst floods into debris flows since this phenomenon
generally starts in slopes 10(Hungr et al., 1984). Smaller
lakes with high or very high outburst susceptibility which are
in the surface range (1.82km2)of failed lakes in Patagonia
more closely resemble their characteristics (i.e. lakes with
steep outlet slopes in contact with glaciers and exposed to
ice avalanches and mass movements) (Fig. 11). The com-
puted (hypothetical) peak discharge of GLOFs from the 28
lakes most susceptible to failure range from 70 to more than
10000 m3s1in the worst scenario (100% of the lake vol-
ume drained) (Fig. 12). However, the complete drainage of
moraine-dammed lakes is uncommon.
The risk from GLOFs remains low in spite of the large
number of glacial lakes existing in the Baker Basin, with 28
lakes having high or very high outburst susceptibility. This is
because the population and infrastructure threatened by out-
burst floods is scarce, since the region is mostly uninhabited
(Fig. 13). Debris flows are the most damaging process trig-
gered by the sudden drainage of glacial lakes since they can
Figure 11. Examples of lakes classified with high or very high out-
burst susceptibility. Steep glaciers, moraines and rock-slopes sur-
round small and medium-sized lakes. Large growing lakes are in
contact with retreating glaciers and have vegetated dams (panel E).
Icebergs are common in proglacial lakes in contact with grounded
glaciers.
Figure 12. Potential peak discharge of GLOFs from lakes with high
or very high outburst susceptibility in the Baker Basin.
develop high-impact pressures, can obstruct rivers causing
back water flooding or floods from the sudden drainage of
these ephemeral lakes. However, not all outburst floods can
develop into debris flows, as they depend on sediment avail-
ability, channel morphology and slope gradient.
We modelled debris flow paths from the 28 moraine-
dammed lakes with higher outburst susceptibility in the
Baker Basin (using the MSF model described in Sect. 2.4.2,
and setting as a source zone the lake area and as stop-
ping condition an angle of reach of 10) and none of them
reached currently inhabited zones (Fig. 14). However, flood
waves travel larger distances and could potentially flood for-
est and agricultural lands, damaging local inhabitants’ liveli-
hoods (Table 5). Floods can also affect transport routes isolat-
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3254 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
Figure 13. Classification of lake outburst susceptibility in the Baker
Basin. Note that most of the lakes with high or very high outburst
susceptibility are located on the west side of the basin.
ing populated areas, as has been demonstrated by historical
events (Hauser, 2000; Worni et al., 2012).
4 Discussion
4.1 Documented outburst floods from
moraine-dammed lakes in Patagonia
The 16 documented lakes that produced outburst floods in
Patagonia are located in areas which became ice free as a
consequence of 20th and early 21th century ice retreat, and
most of the lakes (13, namely 81%) were in contact with
glaciers at the time of failure. Calving-induced waves, the
obstruction of the lakes outlets by icebergs, and the increase
in the hydrostatic pressure over the dams as a result of lake
growth/deepening may explain some of these outburst floods.
The melting of ice-cored moraines also may be related to
dam failures (through dam subsidence or the erosion of oth-
erwise ice-cemented debris (Richardson and Reynolds, 2000;
McKillop and Clague, 2007) since at least one of the failed
moraine-dammed lakes in Patagonia had an ice-core (Worni
et al., 2012). Other recently formed dams, close to glacier
fronts, may also contain buried ice. Thus, most of the out-
burst floods may be an expression of the adjustment of the
landscape to new and evolving glacial conditions after LIA
(Clague and Evans, 2000).
Most of the failed lakes had steep (15) dam outlet
slopes. The higher shear stress in these steep slopes prob-
ably favoured the dam’s erosion when overflows or an in-
crease in the lake discharge occurred. The four largest dams
(50m in height) were covered by mature forest at the time
of failure. However, the vegetation could not stop the pro-
gressive erosion of these steep dams and subsequent catas-
trophic lake drainages. In fact, trees were incorporated in
the flow increasing its damaging capacity. The largest dams
had narrow fronts, closely resembling classic examples of
failed moraine-dammed lakes worldwide (e.g. Lliboutry et
al., 1977). These lakes could be identified as potentially haz-
ardous through a quick examination of aerial photographs
or satellite images. However, two small failed lakes had low
dams with flat and broad surfaces and superficially appeared
stable. A possible factor contributing to their failure is that
lower dams can be easily overtopped by waves or a rise in
lake level since they have less potential freeboard (i.e. there
is less height difference between the lake surface and the low-
est point of the dam).
All the failed lakes were located in areas prone to mass
movements but only one outburst flood was certainly caused
by this phenomenon (Harrison et al., 2006). The dimen-
sions of impact waves, and hence the likelihood of a dam
overtopping, are directly related to the volume and veloc-
ity of the mass movements and the lake bathymetry (Walder
et al., 2003). Large and high-velocity mass movements are
more likely to trigger outburst floods (Walder et al., 2003).
Mass movement modelling shows that lakes in Patagonia
are exposed to this phenomenon. However, frequent low-
magnitude rock-falls, debris flows or snow avalanches are
probably not capable of generating large-impact waves, dam
overtopping, and catastrophic lake drainage.
There is evidence of just one outburst flood that might have
been triggered by an ice avalanche. However, ice avalanche
modelling shows that several failed lakes were located in ar-
eas prone to ice avalanching. The deposits of ice avalanches
can be rapidly obliterated hampering their identification af-
ter few months or years (Kellerer-Pirklbauer et al., 2012).
Thus, this process cannot be discarded as one of the triggers
of other outburst floods. The failure of lakes as a consequence
of an upstream outburst is another potential cause of large
floods (Xin et al., 2008). However, none of the failed lakes
in Patagonia is known to have occurred by this mechanism.
Large lakes (>0.5km2)in areas of low relief are common
in Patagonia and may delay or attenuate outburst floods as
has been demonstrated in the Cachet 2 events (Dussaillant et
al., 2009). Therefore, chain lake ruptures may be restricted
to smaller lakes in high-relief catchment heads which show
quick responses to large and rapid water influxes.
Only two lakes were completely emptied by outburst
floods. This is because moraine dams generally impound
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P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3255
Table 5. Potential damages caused by debris flows and floods originated from moraine-dammed lakes with high or very high outburst
susceptibility in the Baker Basin.
Forest and
Routes (m) Others bush (km2)
Debris flow – Vehicle track – Mining camp (disused) 16
(angle of reach 10)=300 Foot – 1 Bridge – 1 planned dam
paths =1600
Flood (angle – Route 7 =– 1 Bridge in
of reach 5) 1000 – Vehicle secondary route - 1.3
track =300 -1 Bridge in Route 7
Figure 14. GLOF modelling from lakes with high or very high out-
burst susceptibility closest to inhabited zones. Forestry land, routes
and a planned dam are in the path of potential debris flows (angle
of reach 10) and floods. The flow width in D is probably exag-
gerated in its unchannelized path.
only part of the lake’s water volume (the rest of the wa-
ter occurs below the moraine base in overdeepened valleys).
Hence, in spite of the existence of lakes of hundreds of me-
tres in depth in Patagonia (see e.g. Warren et al., 2001), com-
plete lake drainage is unlikely.
Failed moraine-dammed lakes in Patagonia ranged in area
from 0.01 to 1.82 km2. Although larger lakes exist, they have
not failed in historic time. A probable explanation for the fail-
ure of these, comparatively, smaller lakes is that the area and
volume of small lakes can grow quickly after small glacier
changes, dramatically altering the catchment hydrology. Fur-
thermore, large lake systems have had longer periods of ad-
justment (e.g. development of large low-gradient outlets) to
new climatic, glacial and hydrologic conditions since most of
the large lakes were formed during or before the LIA. This
adjustment may have included prehistoric outburst floods
that helped to shape lower and wider outlets.
4.2 Outburst susceptibility classification
Here we have carried out the first systematic analysis of the
conditioning and triggering factors of outburst floods from
moraine-dammed lakes in Patagonia. We weighted these fac-
tors (using the AHP method) to define outburst susceptibility
classes. In conjunction, these data were used to develop a
methodological scheme to assess the outburst susceptibility
of glacier lakes in Patagonia. The approach builds on simi-
lar analyses (e.g. Bolch et al., 2011), however, the weight-
ing of the outburst factors was based on empirical data from
past outburst floods in Patagonia and thus is representative
of the Patagonian geographical context. Thus, it can be used
as a first-order approach to identify hazardous lakes in this
region.
Twelve (75%) of the 16 failed lakes in Patagonia had
scores 65 (other failed lakes had scores ranging from 30
to 49) and thus we selected this score to identify lakes with
high outburst susceptibility. This score does not comprise all
the failed lakes in Patagonia but includes lakes with at least
three characteristics that make them susceptible to failure.
The suggested approach, however, has drawbacks – for ex-
ample, the omission of dam characteristics in the analysis
and the subjectivity of the weighting scheme. Furthermore,
the rapid nature of glacier changes in Patagonia (see Davies
and Glasser, 2012) means that this analysis needs to be up-
dated regularly.
The use of medium-resolution (15–30m) satellite images
and DEMs limit the inclusion of dam characteristics that
can be critical to explain outburst floods, such as dam free-
board and resistance to erosion. However, these resources al-
low a rapid extraction of data from hundreds of lakes in a
short time. The relatively coarse spatial resolution of the im-
agery means that distinguishing between lakes dammed by
moraines and bedrock was not straightforward in all cases.
In some examples, categorical identification of features is
not even possible using finer-resolution satellite images and
aerial photographs. Thus, detailed local-scale analyses of the
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3256 P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia
Figure 15. Geomorphic effects of an outburst flood (Los Leones
Valley) produced by the impact of a rock avalanche. The small lake,
detached from the glacier tongue at the time of failure, was clas-
sified with low outburst susceptibility in spite of the steep outlet
slope. Note the elevated traces (40m) of the impact wave and the
large boulders (>6m in diameter) transported by the flow.
lakes classified with high or very high outburst susceptibility
needs to be carried out to judge whether outburst preventive
or mitigation measures are required. The identification of po-
tential source of mass movements (slope steepness and veg-
etation coverage) can be refined using empirical data from
landslide inventories in glacial and periglacial belts in Patag-
onia, or geomorphic features such as fresh scars and landslide
deposits.
Although the weighting scheme used in the Baker Basin
is subjective, it has the advantage of being based on GLOFs
conditioning and triggering factors in Patagonia. It is thus
better suited to the identification of potentially hazardous
lakes in this region than approaches developed for other ge-
ographical contexts. Furthermore, the evaluation of the con-
sistency of the judgments in the weighting scheme (Table 3)
is an advantage of the AHP method in relation to other qual-
itative or semi-quantitative approaches used in GLOF hazard
assessments (see Emmer and Vilímek, 2013, for a review).
Glacier fluctuations can shift the source area of ice
avalanches and expand or generate new glacial lakes, result-
ing in a change in outburst susceptibility and hazard over
time (Huggel et al., 2001, 2004). This makes periodic mon-
itoring of glaciers, lakes and their surroundings necessary
in Patagonia, particularly near inhabited areas or critical in-
frastructure. The rapid growth of the Olvidado Lake three
years before the outburst in 2003 is an example of the speed
at which glacier and lake changes can occur in this region
(Rivera and Casassa, 2004).
In the Baker Basin 28 lakes were classified with high or
very high outburst susceptibility. Most of the lakes are lo-
cated in uninhabited valleys or dozens of kilometres from set-
tlements or infrastructure. However, modelled debris flows
and floods from hazardous lakes reached forestry land, a
planned dam, and transportation routes. Damage to access
routes by GLOFs can increase accessibility problems faced
by Patagonian settlements (Muñoz et al., 2006). These 28
lakes, based on the results of this study, are more suscepti-
ble to failure than other lakes. However, this does not imply
that other lakes cannot also fail. For example, large, albeit
infrequent, landslides or ice avalanches can cause the sudden
drainage of otherwise stable lakes (Fig. 15).
The approach used in this study has the advantage that can
be applied at regional-scale using publicly available satellite
images and DEMs allowing the analysis of hundreds of lakes
in an inexpensive way. Also, it is based on simple and robust
image classification and flow modelling techniques proven in
different geographical settings (Paul et al., 2002; Huggel et
al., 2003; Frey et al., 2010b; Bolch et al., 2011). Thus, it is
suitable for identifying the lakes most susceptible to fail in
Patagonia as a first approach to GLOF hazard assessments.
5 Conclusions
We analysed 16 historic outburst floods from moraine-
dammed lakes in Patagonia and our analysis shows that lakes
in contact with glaciers and having moderate (8) to steep
(15) outlet slopes are more likely to fail. The influence of
other factors, such as dam height and vegetation coverage,
on the lake outburst susceptibility is less clear. The dam ge-
ometry and vegetation coverage, however, had a direct influ-
ence on the flow hydrology (e.g. peak discharge and debris
transport) and hence the damage potential of flows. GLOF
paths in Patagonia display a rapid decrease in damage poten-
tial downstream of the lakes. Most of the steep path slopes
favouring debris flow occurrence and fast flows (the most
damaging processes linked with GLOFs) were at distances
3000m from failed dams. However, as has been demon-
strated by historical events, attenuated flows might still en-
danger widespread areas in unconfined valleys. Furthermore,
wood transport has been common during GLOFs and can af-
fect distant zones.
The characteristics of failed lakes in Patagonia were used
to develop an outburst susceptibility scheme (based on the
AHP method and remote sensing and GIS techniques) which
was applied in the Baker Basin, Chilean Patagonia. The
scheme allowed categorizing the outburst susceptibility of
hundreds of lakes in a short time in a qualitative, yet repro-
ducible way. The scheme integrated data from past GLOFs
in Patagonia making it suitable for wider application in the
region. The scheme might be used to complement GLOF
hazard assessments in Patagonia which until now have re-
lied mostly on statistical analysis of short-term series of flood
data. The identification of the lakes more susceptible to fail-
ure, and the empirical modelling of the floods, are first steps
toward a full GLOF hazard assessment which should ulti-
mately include data on potential flood intensity (e.g. flood
Nat. Hazards Earth Syst. Sci., 14, 3243–3259, 2014 www.nat-hazards-earth-syst-sci.net/14/3243/2014/
P. Iribarren Anacona et al.: Moraine-dammed lake failures in Patagonia 3257
volume, velocity and sediment entrainment/deposition) and
GLOF probability in a determined time span.
Acknowledgements. We thank Rodrigo Iribarren for assistance in
the field. This work was improved by the constructive reviews of
Martin Mergili, Adam Emmer and an anonymous reviewer, and
by the comments of the Editor Paolo Tarolli. Michael Crozier is
also thanked for his comments on an earlier draft of this paper. P.
Iribarren Anacona is a Becas Chile fellow.
Edited by: P. Tarolli
Reviewed by: M. Mergili, A. Emmer, and one anonymous referee
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... The glacier recession in the last decades has resulted in a considerable increase in the number and size of the glacial lakes across the Andes , but also the noticeable increase in the catastrophic events derived by changes in the cryosphere during the last century. Glacier and permafrost hazards such as Glacial Lake Outburst Floods (GLOFs), permafrost degradation, glacier detachment and its subsequent debris flow, slope instability triggering landslides, rock-ice avalanches (Dussaillant et al., 2009;Iribarren-Anacona et al., 2014Wilson et al., 2018Wilson et al., , 2019 In terms of hazards derived from glacial lakes, most of those lakes in the Southern Andes are impounded by moraine-dams or icedams. The potential failure of the dammed lake can release thousands to millions of cubic meters of water in a very short period of time, affecting downstream communities and essential infrastructure. ...
... GLOFs can occur or be initiated by different mechanisms, the most common with the moraine-dammed lakes overtopping. The overtopping can be accomplished by mass movement, ice avalanches, debris flows, and calving processes resulting in a progressive failure of the structure of the moraine (Haerberli, 1983;Emmer and Vilímek, 2013;Mergili et al., 2013Iribarren-Anacona et al., 2014 and can induce cascading hazards often related to a changing cryosphere (Richarson and Reynolds, 2000;Haeberli and Whiteman, 2014). Another mechanism that can potentially trigger a GLOF is seismic activity . ...
... In total more than 30 ice and moraine dammed lakes have failed since the 18 th century (Iribarren-Anacona et al., 2014), including the largest event at Perito Moreno Glacier, where 5000 x 10 6 m 3 of water were added to the Lago Argentino in 1956 (Walder and Costa, 1996). More recently in the Chileno Valley (NPI) a large GLOF event occurred in December 2015. ...
Thesis
Glaciers on Earth along other components of the cryosphere are important for the climate system. However, it is widely known that the vast majority of glaciers are retreating and thinning since the early part of the 20th century. Additionally, future projections have highlighted that at the end of the 21st century, glaciers are going to lose a considerable part of their remaining mass. These glacier changes have several implications for physical, biological and human systems, affecting the water availability for downstream communities and contribute to sea level rise. Unlike other regions, where glaciers are less relevant for the overall hydrology, glaciers in South America constitute a critical resource since minimum flow levels in headwaters of the Andean mountains are usually sustained by ice melt, especially during late summer and droughts, when the contribution from the seasonal snow cover is depleted. In the last decades, the number of studies has increased considerable, however, in the Southern Andes and the surrounding sub-Antarctic islands glaciers still are less studied in comparison with their counterparts in the Northern Hemisphere. The few studies on glacier mass balance in this region suggest a risk of water scarcity for many Andean cities which freshwater supply depends on glacial meltwater. Additionally, glaciers on sub-Antarctic islands have not been completely assessed and their contribution to the sea level rise has been roughly estimated. Hence, the monitoring of glaciers is critical to provide baseline information for regional climate change adaptation policies and facilitate potential hazard assessments. Close and long-range remote sensing techniques offer the potential for repeated measurements of glacier variables (e.g. glacier mass balance, area changes). In the last decades, the number of sensors and methods has increased considerably, allowing time series analysis as well as new and more precise measurements of glacier changes. The main goal of this thesis is to investigate and provide a detailed quantification of glacier elevation and mass changes of the Southern Andes with strong focus on the Central Andes of Chile and South Georgia. Six comprehensive studies were performed to provide a better understanding of the development and current status of glaciers in this region. Overall, the glacier changes were estimated by means of various remote sensing techniques. For the Andes as a whole, the first continent-wide glacier elevation and mass balance was conducted for 85% of the total glacierized area of South America. A detailed estimation of mass changes using the bi-static synthetic aperture radar interferometry (Shuttle Radar Topography Mission -SRTM- and TerraSAR-X add-on for Digital Elevation Measurements -TanDEM-X- DEMs) over the years 2000 to 2011/2015 was computed. A total mass loss rate of 19.43 ± 0.60 Gt a-1 (0.054 ± 0.002 mm a-1 sea level rise contribution) from elevation changes above ground, sea or lake level was calculated, with an extra 3.06 ± 1.24 Gt a-1 derived from subaqueous ice mass loss. The results indicated that about 83% of the total mass loss observed in this study was contributed by the Patagonian icefields (Northern and Southern), which can largely be explained by the dynamic adjustments of large glaciers. For the Central Andes of Chile, four studies were conducted where detailed times series of glacier area, mass and runoff changes were performed on individual glaciers and at a region level (Maipo River basin). Glaciers in the central Andes of Chile are a fundamental natural resources since they provide freshwater for ecosystems and for the densely populated Metropolitan Region of Chile. The first study was conducted in the Maipo River basin to obtain time series of basin-wide glacier mass balance estimates. The estimations were obtained using historical topographic maps, SRTM, TanDEM-X, and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results showed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, with more negative values between 2000 and 2013. A mean basin-wide glacier mass balance of −0.12 ± 0.06 m w.e. a-1 , with a total mass loss of 2.43 ± 0.26 Gt between 1955–2013 was calculated. For this region, a 20% reduction in glacier ice volume since 1955 was observed with associated consequences for the meltwater contribution to the local river system. Individual glacier studies were performed for the Echaurren Norte and El Morado glaciers. Echaurren Norte Glacier is a reference glacier for the World Glacier Monitoring Service. An ensemble of different data sets was used to derive a complete time series of elevation, mass and area changes. For El Morado Glacier, a continuous thinning and retreat since the 20th century was found. Overall, highly negative elevation and mass changes rates were observed from 2010 onwards. This coincides with the severe drought in Chile in this period. Moreover, the evolution of a proglacial lake was traced. If drained, the water volume poses an important risk to down-valley infrastructure. The glacier mass balance for the Central Andes of Chile has been observed to be highly correlated with precipitation (ENSO). All these changes have provoked a glacier volume reduction of one-fifth between 1955 and 2016 and decrease in the glacier runoff contribution in the Maipo basin. The thesis closes with the first island-wide glacier elevation and mass change study for South Georgia glaciers, one of the largest sub-Antarctic islands. There, glaciers changes were inferred by bi-static synthetic aperture radar interferometry between 2000 and 2013. Frontal area changes were mapped between 2003 and 2016 to roughly estimate the subaqueous mass loss. Special focus was given to Szielasko Glacier where repeated GNSS measurements were available from 2012 and 2017. The results showed an average glacier mass balance of −1.04 ± 0.09 m w.e. a-1 and a mass loss rate of 2.28 ± 0.19 Gt a-1 (equivalent to 0.006 ± 0.001 mm a-1 sea level rise) in the period 2000-2013. An extra 0.77 ± 0.04 Gt a-1 was estimated for subaqueous mass loss. The concurrent area change rate of the marine and lake-terminating glaciers amounts to −6.58 ± 0.33 km2 a-1 (2003–2016). Overall, the highest thinning and retreat rates were observed for the large outlet glaciers located at the north-east coast. Neumayer Glacier showed the highest thinning rates with the disintegration of some tributaries. Our comparison between InSAR data and GNSS measurements showed good agreement, demonstrating consistency in the glacier elevation change rates from two different methods. Our glacier elevation and mass changes assessment provides a baseline for further comparison and calibration of model projection in a sparsely investigated region. Future field measurements, long-term climate reanalysis, and glacier system modelling including ice-dynamic changes are required to understand and identify the key forcing factors of the glacier retreat and thinning.
... Bolch et al., 2011, Rounce et al, 2016). In line with global observations ( Carrivick and Tweed, 2016), the majority of the GLOF events in Chile and Argentina have resulted from the failure of ice dammed lakes, many of which have developed beside outlet glaciers of the Northern and Southern Patagonia Icefield (NPI and SPI) ( Iribarren Anacona et al., 2014). Unlike moraine dammed lakes, which rarely fail more than once, ice dammed lakes can often fail repeatedly on a regular or irregular basis. ...
... Despite this situation, monitoring of glacial lake development and evolution in Chile and Argentina has been limited, with past investigations only covering relatively small regions of Patagonia (e.g. Loriaux and Casassa, (2013), Iribarren Anacona et al. (2014) and Paul and Mölg (2014)). In response to current limitations, this study aims to characterise the physical attributes, spatial distribution and temporal development of glacial lakes in the Central and Patagonian Andes through the use of Landsat satellite imagery (acquired in ̴ 1986, ̴ 2000 and ̴ 2016) and other high-resolution image datasets available in Google Earth and Bing Maps. ...
... Previous studies have attempted to rank glacial lake failure susceptibility and determine downstream impacts using medium resolution satellite-derived imagery and elevation data as part of quantitative, semi-quantitative and qualitative GLOF hazard, vulnerability and risk assessment approaches (e.g. Iribarren Anacona et al., 2014;Emmer et al., 2016;Rounce et al., 2016). During such approaches, GLOF generation parameters and their relative importance for a given area are chosen either (1) statistically (quantitatively)-based on physical measurements and/or observations, (2) subjectively (qualitatively)-according to the experience of the researchers, or (3) through a combination of statistical and subjective assessment (semi-quantitatively) ( Emmer & Vilimek, 2013). ...
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The prevalence and increased frequency of high-magnitude Glacial Lake Outburst Floods (GLOFs) in the Chilean and Argentinean Andes suggests this region will be prone to similar events in the future as glaciers continue to retreat and thin under a warming climate. Despite this situation, monitoring of glacial lake development in this region has been limited, with past investigations only covering relatively small regions of Patagonia. This study presents new glacial lake inventories for 1986, 2000 and 2016, covering the Central Andes, Northern Patagonia and Southern Patagonia. Our aim was to characterise the physical attributes, spatial distribution and temporal development of glacial lakes in these three sub-regions using Landsat satellite imagery and image datasets available in Google Earth and Bing Maps. Glacial lake water volume was also estimated using an empirical area-volume scaling approach. Results reveal that glacial lakes across the study area have increased in number (43%) and areal extent (7%) between 1986 and 2016. Such changes equate to a glacial lake water volume increase of 65?km3 during the 30-year observation period. However, glacial lake growth and emergence was shown to vary sub-regionally according to localised topography, meteorology, climate change, rate of glacier change and the availability of low gradient ice areas. These and other factors are likely to influence the occurrence of GLOFs in the future. This analysis represents the first large-scale census of glacial lakes in Chile and Argentina and will allow for a better understanding of lake development in this region, as well as, providing a basis for future GLOF risk assessments.
... In a study conducted for the Swiss Alps,Huggel et al. (2004)described that the assessment of such threats must consider basic glaciological, geomorphological and hydraulic principles together with experiences gained from previous events (Fig. 1a–d). GLOF events have widely been reported around the world's high mountains (Carrivick and Tweed, 2016;Emmer et al., 2016a) including the Himalayas (Worni et al., 2013;Komori, 2008;Bolch et al., 2008Bolch et al., , 2010Wang, 2016), Tien Shan (Bolch et al., 2012b(Reynolds, 2014), Alps (Huggel et al., 2002), Peruvian Andes (Lliboutry et al., 1977;), Canadian Rockies (Clague and Evans, 2000) and Chilean Patagonia (Worni et al., 2012;Anacona et al., 2014). The present study is focused on Sikkim Himalaya, India and research studies indicate that glacial lakes in Sikkim are increasing in number and size (e.g.). ...
... An intensity-likelihood matrix for Lake Palcacocha (Somos-Valenzuela et al., 2016) and combinations of vulnerability and exposure indices (IPCC, 2014;Allen et al., 2016) have also been applied to estimate the GLOF hazard. The Analytic Hierarchy Processes (AHP) method used in the current study (see Section 3.5) has already been widely used to assess natural hazards (Ayalew et al., 2005;Lari et al., 2009;Anacona et al., 2014;Wang et al., 2015;Wang, 2016) and allows to evaluate the consistency (Saaty, 1980) of the judgements based on the estimation of the eigenvalues of the factors matrix. ...
... There is no established statistical procedure to determine the probability of a GLOF event (ICIMOD, 2011). In the present study, a widely used scientific based approach called WIOA using AHP (Anacona et al., 2014) was employed to prioritise the susceptibility of previously selected 21 hazardous glacial lakes (see Section 3.4) to outburst flood. AHP is a pairwise comparison matrix, which expresses the relative preference among the factors. ...
Article
Climatic changes alter the climate system, leading to a decrease of glacier mass volumes and swelling glacial lakes. This study provides a new inventory of glacial and high-altitude lakes for Sikkim, Eastern Himalaya, and evaluates the susceptibility of lakes to Glacial Lake Outburst Flood (GLOF). By using satellite data of high spatial resolution (5 m), we obtain 1104 glacial and high-altitude lakes with total area 30.498 km2, of which 472 have an area > 0.01 km2. Applying pre-defined GLOF susceptibility criteria on these 472 lakes yields 21 lakes susceptible to GLOF, which all increased in area from 1972–2015. Using Analytic Hierarchy Processes (AHP), the pairwise comparison matrix further reveals that 5 of these glacial lakes have low, 14 have medium and 2 have high GLOF susceptibility. Especially these 16 glacial lakes with high and medium GLOF susceptibility may threaten downstream communities and infrastructure and need further attention. http://www.sciencedirect.com/science/article/pii/S0169555X1630887X
... Los Ñadis). These floods occurred due to the catastrophic drainage of moraine-dammed lakes located in steep catchment heads (Iribarren Anacona et al., 2014). The bedload transport during GLOFs might be significant but has not yet been measured. ...
... The landscape of the Baker basin is particularly dominated by glacial landforms and deposits owing to episodes of glacier advance and recession . Glaciers are currently covering 1940 km 2 of the basin (7%) and have retreated since Little Ice Age forming lakes and exposing drift-mantled slopes and massive diamictons in the main valleys (Davies and Glasser, 2012;Iribarren Anacona et al., 2014). Sediment supply from deglaciated slopes and redeposition of glacial till resulted in large outwashes and braided rivers (e.g. ...
Article
Characterizing river corridors from a hydro-morphological standpoint is a fundamental requisite for the analysis of their past evolution and for the plausible prediction of how rivers may adjust to changing climatic conditions and to increasing human impacts. The River Baker (Chilean Patagonia) is a highly dynamic fluvial system with relatively limited human intervention, which flows throughout a mountainous landscape following a narrow floodplain which widens towards the Pacific Ocean. Here, we characterize its current morphology as a basis for understanding its geomorphic dynamics, using satellite images as data source and following a hierarchical classification procedure. The Baker was divided into 9 segments and 34 reaches based on channel confinement and geometry. The geomorphic classification resulted in several confined (41%) and semiconfined (53%) reaches, whereas only 6% of them were classified as unconfined. Most of the confined reaches were single thread and the majority of the semiconfined ones were sinuous. Braided reaches were identified in all confinement categories and represent 30% of the reaches. We identified and characterized 246 islands and 393 fluvial bars and delimited 170 wetlands. Finally, we could statistically relate the island density to the braiding index, active channel width and sinuosity index, whereas the presence of bars is influenced by the active channel width, and degree of braiding and sinuosity. This characterization represents a starting point in the geomorphological analysis of the river and serves as a basis to plan future investigation efforts aiming at unravelling the morpho-dynamics of this unexplored large austral fluvial system.
... It appears that at Imja and Lower Barun Lakes it may have contributed to the higher retreat rates and increased calving more than at the relatively smaller and more shallow Thulagi Lake. Furthermore, glacial lakes with calving ice fronts are also linked with a relatively higher likelihood of failure [45,[93][94][95], adding further to the hazard posed by both Imja and Lower Barun Lakes. ...
... Identifying the possible triggers at each lake, the range of associated hazards, and the percentage and rates of water spilling out of the lakes is beyond the scope of this paper. In general, potential failures and prospects for damaging GLOFs is dependent upon on the volume of lake-water; the lakes' topographic settings and unstable surroundings; the pattern of lake evolution; the type and rapidity of breach and seepage coming through the unconsolidated (or poorly consolidated) end moraine, indicating the piping of water and instability of the moraine; and of course the vulnerabilities downstream from the lakes [17,30,94,127,128]. ...
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Glacier recession driven by climate change produces glacial lakes, some of which are hazardous. Our study assesses the evolution of three of the most hazardous moraine-dammed proglacial lakes in the Nepal Himalaya—Imja, Lower Barun, and Thulagi. Imja Lake (up to 150 m deep; 78.4 × 106 m3 volume; surveyed in October 2014) and Lower Barun Lake (205 m maximum observed depth; 112.3 × 106 m3 volume; surveyed in October 2015) are much deeper than previously measured, and their readily drainable volumes are slowly growing. Their surface areas have been increasing at an accelerating pace from a few small supraglacial lakes in the 1950s/1960s to 1.33 km2 and 1.79 km2 in 2017, respectively. In contrast, the surface area (0.89 km2) and volume of Thulagi lake (76 m maximum observed depth; 36.1 × 106 m3; surveyed in October 2017) has remained almost stable for about two decades. Analyses of changes in the moraine dams of the three lakes using digital elevation models (DEMs) quantifies the degradation of the dams due to the melting of their ice cores and hence their natural lowering rates as well as the potential for glacial lake outburst floods (GLOFs). We examined the likely future evolution of lake growth and hazard processes associated with lake instability, which suggests faster growth and increased hazard potential at Lower Barun lake.
... A multicriteria Analytical Hierarchy Process (AHP) method is used to assess the magnitude (e.g., low, medium, and high) of glacial lakes susceptibilities. AHP based multi-criteria has been widely employed in other regions for outbursts susceptibility assessment [28][29][30][31][32][33]. Similar techniques for examining the outbursts susceptibility were used in Uzbekistan [34], Cordillera blanca, Peru [18], and the Himalayan region [35]. ...
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Northern latitudes of Pakistan are warming at faster rate as compared to the rest of the country. It has induced irregular and sudden glacier fluctuations leading to the progression of glacial lakes, and thus enhancing the risk of Glacier Lake Outbursts Floods (GLOF) in the mountain systems of Pakistan. Lack of up-to-date inventory, classification, and susceptibility profiles of glacier lakes and newly formed GLOFs, are few factors which pose huge hindrance towards disaster preparedness and risk reduction strategies in Pakistan. This study aims to bridge the existing gap in data and knowledge by exploiting satellite observations, and efforts are made to compile and update glacier lake inventories. GLOF susceptibility assessment is evaluated by using Analytical Hierarchy Process (AHP), a multicriteria structured technique based on three susceptibility contributing factors: Geographic, topographic, and climatic. A total of 294 glacial lakes are delineated with a total area of 7.85 ± 0.31 km 2 for the year 2018. Analysis has identified six glacier lakes as potential GLOF and met the pre-established criteria of damaging GLOFs. The historical background of earlier GLOF events is utilized to validate the anticipated approach and found this method appropriate for first order detection and prioritization of potential GLOFs in Northern Pakistan.
... ASTER GDEM V2 was acquired from the Earth Remote Sensing Data Analysis Centre (ERSDAC), Japan ( Tachikawa et al. 2011). The spatial characteristics such as glacier catchment, surface gradient, lake area, glacier-lake interface and outlet slope are the important factors used to determine the outburst potentials ( Anacona et al. 2014). Spatial characteristics for both basins and lakes were extracted from above data in ArcGIS 10 environment. ...
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Geospatial studies carried out in two major proglacial lakes of Samudra Tapu and Gepang Gath (Chandra basin, Western Himalaya) showed substantial expansion in their area and volume over the last four decades (1971-2014). The linear and areal expansions for the lakes Samudra Tapu and Gepang Gath were 1889 m, 1509 m and 1 km2, 0.6 km2 respectively. The results show that increased melting of the feeder glaciers over this period is major contributor to expand the volumes approximately 20 times of both the lakes Samudra Tapu and Gepang Gath. This expansion of lakes volume of Samudra Tapu and Gepang Gath from 3.4 x 106 m3 to 67.7 x 106 m3 and 1.5 x 106 m3 to 27.5 x 106 m3 respectively are quite significance in terms of hazards generated from GLOF. This kind of climate change induced increase in the rate of glacial melting is a cause of concern, as the Himalaya Mountains may turn out to be vulnerable to natural hazards like Glacial Lake Outburst Floods (GLOF).
... Indeed this sea level contribution is~10% of that from all glaciers and ice caps worldwide (Rignot et al., 2003). Over the next two centuries, mass loss from these glaciers has implications for sea level rise (Braithwaite and Raper, 2002;Gardner et al., 2013;Glasser et al., 2011;Levermann et al., 2013), for increased hazards from glacial lake outburst floods (Anacona et al., 2014;Dussaillant et al., 2009;Harrison et al., 2006;Loriaux and Casassa, 2013), and for water resources. ...
Article
South American glaciers, including those in Patagonia, presently contribute the largest amount of meltwater to sea level rise per unit glacier area in the world. Yet understanding of the mechanisms behind the associated glacier mass balance changes remains unquantified partly because models are hindered by a lack of knowledge of subglacial topography. This study applied a perfect-plasticity model along glacier centre-lines to derive a first-order estimate of ice thickness and then interpolated these thickness estimates across glacier areas. This produced the first complete coverage of distributed ice thickness, bed topography and volume for 617 glaciers between 41oS and 55oS and in 24 major glacier regions. Maximum modelled ice thicknesses reach 1631 m ± 179 m in the South Patagonian Icefield (SPI), 1315 m ± 145 m in the North Patagonian Icefield (NPI) and 936 m ± 103 m in Cordillera Darwin. The total modelled volume of ice is 1234.6 km³ ± 246.8 km³ for the NPI, 4326.6 km³ ± 865.2 km³ for the SPI and 151.9 km³ ± 30.38 km³ for Cordillera Darwin. The total volume was modelled to be 5955 km³ ± 1191 km³, which equates to 5458.3 Gt ± 1091.6 Gt ice and to 15.08 mm ± 3.01 mm sea level equivalent (SLE). However, a total area of 655 km² contains ice below sea level and there are 282 individual overdeepenings with a mean depth of 38 m and a total volume if filled with water to the brim of 102 km³. Adjusting the potential SLE for the ice volume below sea level and for the maximum potential storage of meltwater in these overdeepenings produces a maximum potential sea level rise (SLR) of 14.71 mm ± 2.94 mm. We provide a calculation of the present ice volume per major river catchment and we discuss likely changes to southern South America glaciers in the future. The ice thickness and subglacial topography modelled by this study will facilitate future studies of ice dynamics and glacier isostatic adjustment, and will be important for projecting water resources and glacier hazards.
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Climatic change-induced glacier recession has been accompanied by formation and growth of proglacial lakes in the Himalayan region, which pose an emerging significant threat to the downstream communities/settlements in the form of outburst floods. To understand spatiotemporal evolution patterns, sources and driving mechanism of formation and expansion of glacial lakes, a temporal inventory of glacial lakes (area > 2000 m²) in Chandra basin has been developed from 2000 to 2014 using IRS LISS-III images. From 2000 to 2014, the total number of glacial lakes in Chandra basin increased from 28 to 46 and area expanded from 1.91 ± 0.24 km² to 3.26 ± 0.24 km². Glacier recession and increased glacier melt runoff due to climate warming led to the formation and expansion of glacial lakes in space vacated by glacier recession. The increase in number and area of ice-dammed lakes at higher elevations confirms the continued glacier retreat in the basin. Lakes in contact or in the proximity of the mother glacier exhibit higher growth and formation rate. The accelerated growth of glacial lakes has resulted in increased hazard and damage potential of glacial lake outburst floods in Chandra basin. Seven potentially dangerous lakes are identified and analysed qualitatively for outburst probability.
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Large water waves generated by landslides impacting with a body of water are known from Disenchantment and Lituya Bays, Alaska; Vaiont reservoir, Italy; Yanahuin Lake, Peru; Shimabara Bay, Japan; and many fiords in Norway. The combined death toll from these events most likely exceeds 20,000 people. Such waves may be oscillatory, solitary, or bores and nonlinear mathematical theories or linearizing assumptions are thus needed to describe their wave amplitudes, celerities, and periods. In this paper the following approaches are compared: (1) the Noda simulation of a vertically falling and horizontally moving slide by linearized impulsive wave theory and estimation of nonlinear wave properties; (2) the Raney and Butler modification of vertically averaged nonlinear wave equations written for two horizontal dimensions to include three landslide forcing functions, solved numerically over a grid for wave amplitude and celerity; (3) the empirical equations of Kamphuis and Bowering, based on dimensional analysis and two-dimensional experimental data; and (4) an empirical equation developed in this report from three-dimensional experimental data, i.e., log(ηmax/d) = a + b log(KE), where a, b = coefficients, ηmax = predicted wave amplitude, d = water depth, and KE = dimensionless slide kinetic energy. Beyond the slide area changes in waveform depend upon energy losses, water depth and basin geometry and include wave height decrease, refraction, diffraction, reflection, and shoaling. Three-dimensional mathematical and experimental models show wave height decrease to be a simple inverse function of distance if the remaining waveform modifiers are not too severe. Only the Raney and Butler model considers refraction and reflection. Run-up from waves breaking on a shore can be conservatively estimated by the Hall and Watts formula and is a function of initial wave amplitude, water depth, and shore slope. Predicted run-ups are higher than experimental run-ups from three-dimensional models. The 1958 Lituya Bay and 1905 Disenchantment Bay, Alaska events are examined in detail, and wave data are developed from field observations. These data and data based on a Waterways Experiment Station model are compared to wave hindcasts based on various predictive approaches, which yield a large range of predicted wave heights. The most difficult problems are in matching the exact basin geometry and estimating slide dimensions, time history, and mode of emplacement. Nevertheless, the hindcasts show that the mathematical and experimental model approaches do provide useful information upon which to base engineering decisions. In this regard the empirical equation developed in this report is at least as satisfactory as existing methods, and has the advantage of requiring less complicated input data.
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Floods from failures of natural and constructed dams constitute a widespread hazard to people and property. Expeditious means of assessing flood hazards are necessary, particularly in the case of natural dams, which may form suddenly and unexpectedly. We revise statistical relations (derived from data for past constructed and natural dam failures) between peak discharge (Q(p)) and water volume released (V(0)) or drop in lake level (d) but assert that such relations, even when cast into a dimensionless form, are of limited utility because they fail to portray the effect of breach-formation rate. We then analyze a simple, physically based model of dam-breach formation to show that the hydrograph at the breach depends primarily on a dimensionless parameter η = kV 0/g 1/ 2d 7/ 2, where k is the mean erosion rate of the breach and g is acceleration due to gravity. The functional relationship between Q(p) and η takes asymptotically distinct forms depending on whether η << 1 (relatively slow breach formation or small lake volume) or η >> 1 (relatively fast breach formation or large lake volume). Theoretical predictions agree well with data from dam failures for which k, and thus η, can be estimated. The theory thus provides a rapid means of predicting the plausible range of values of peak discharge at the breach in an earthen dam as long as the impounded water volume and the water depth at the dam face can be estimated.
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A study intended to be mainly of practical use in the prediction of ice-avalanche hazards was carried out. About 100 ice avalanches, mostly from the Alps, were documented. Starting zones of these ice avalanches could be classified by using simple terrain characteristics. Ice avalanches from some starting zones at relatively low altitudes and with large, homogeneously inclined bedrock planes occur predominantly in summer and autumn. No such seasonal variation in frequency was found in connection with other types of starting zones occurring either at higher altitudes or involving abrupt changes of the bedrock’s gradient. One- and two-parameter models for the estimation of run-out distances of landslides and snow avalanches were tested for their use with ice avalanches. Introduction of the second (v 2 proportional) frictional parameter leads only to moderately improved accuracy in the prediction of run-out distances. For relatively short run-out distances (several hundred meters), an alternative method of estimation, based on terrain characteristics, is proposed.
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Cascade Range alpine glaciers have shrunk substantially as average annual temperature has risen 0.5 to 2 degrees Celsius since culmination of the Little Ice Age in the mid- to late 1800's. In recently deglaciated areas in the Cascade Range, hundreds of lakes have formed. Most of these newly formed lakes are partly or entirely bound by bedrock rims and are stable, but at least 30 are dammed by unconsolidated moraines that are susceptible to breaching. The highest concentration of lakes dammed by Neological moraines in the conterminous United States is in the Mount Jefferson and Three Sisters Wilderness Areas in central Oregon, where there are currently eight moraine-dammed lakes. The largest lake, Carver Lake on South Sister, has a volume of almost 1 million cubic meters. Most of these lakes formed between 1920 and 1940 during a period of substantial warming and glacier retreat. In the Mount Jefferson and Three Sisters Wilderness Areas, there have been 11 debris flows from 4 complete and 7 partial emptyings of moraine-dammed lakes. Most of these breaches occured between 1930 and 1950, but some were as recent as the 1970's. All moraine-dam breaches in the Three Sisters and Mount Jefferson Wilderness Areas occurred during the melt season (July-October), usually during periods of warm or rainy weather. Many breaches were probably a result of erosion of the steep outlet channels, triggered by unusually large discharges caused by (1) waves generated by rockfalls or ice avalanches into the lake or (2) increased lake outflow caused by precipitation and melting snow and ice. Water flows from breached moraine dams rapidly evolved into debris flows that traveled as far as 9 kilometers before stopping or evolving into sediment-laden water flows. Peak discharges of at least four of the flows exceeded 300 cubic meters per second. Flows from breached morainal dams transformed from clear water at the outlet into debris flows within 500 meters of the breaches by incorporating large volumes of loose Neoglacial till and outwash from the moraines and proglacial outwash. For the two largest lake releases, the volume of sediment eroded near the outlet exceeded 25 percent of the total volume of water released. Morphological evidence indicates that sediment was introduced into flows by bank collapse and channel incision. Indirect discharge estimates (primarily by a critical-depth procedure) show that peak discharges increased in erosional reaches; in one instance by more than a factor of four. Erosion and sediment entrainment was restricted to reaches with slopes that exceeded 8°, and deposition occured in reaches with slopes less than 18°. Several moraine-dammed lakes still exist, and some pose downstream hazards. Two of the lakes are remnants of previously larger lakes that have partially breached their moraine dams. Five lakes in the Three Sisters and Mount Jefferson Wilderness Areas are impounded by Neoglacial moraines that have not been breached. Qualitative assessments of downstream hazards from moraine-dammed lakes are possible on the basis of the topographic setting of the lake and downstream channel conditions. Quantitative assessment of the likelihood of breaching or the magnitude of downstream flows is difficult because of the variety of mechanisms that trigger breaches, the sensitivity of outflow hydrographs to breach shape and erosion rate, and the large uncertainty of downstream flow characteristics.
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Landscape concept implies several qualities and meanings. Considering this, a method for its integral appraisal is presented to be applied in the water landscapes in the river Baker basin, Aysén region. This it is an exceptional territory because of its heterogeneousness, singularity, and environmental quality, territorial and social importance of the aquatic systems that constitute it. The conceptual bases for the integral appraisal of these water landscapes has as reference for the analysis orientated to main cultural and physical qualities. The objective is to value these landscapes like spatial expression of a geographical context, as a setting for the action of the man, an identity bearer environment, an indicator of the environmental quality and a component of the territory that is essential to support determined activities, like tourism. An analysis oriented in the perspectives enunciated will permit to build a method of appraisal of the water landscapes that can support the river Baker basin management and other similar territories, rescuing the various meanings and functions of the landscape.
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An approach for semi-automatic lake detection based on multispectral optical remote sensing data and digital elevation models (DEM) is presented in this contribution. After preprocessing of the satellite images, all data are processed in a Geographic Information System (GIS). Preliminary hazard assessment of the detected lakes in a test region was performed: Potential ice avalanches and debris fl ows originating in glacier lake outbursts are modeled by means of hydrological fl ow-routing models. The strength of the presented methods is the ability to quickly create an overview of the glacier lake situation and related hazard potentials over large regions. With few adjustment works, the presented approach can be applied to mountain regions all over the world.
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Field and geophysical studies have allowed us to identify processes leading to ice-cored moraine degradation for three natural dams investigated in Peru and Nepal. As potentially hazardous lakes form on the snouts of debris-covered glaciers they may separate a stagnant ice body from the upper reaches of the glacier to form an ice-cored end-moraine complex. The ice-cored moraines appear to degrade through ablation beneath the debris cover, by localized thermokarst development, and by associated mass movement. Relict glacier structures serve as a focal point for the onset of accelerated thermokarst degradation. Once exposed, the ice core then undergoes accelerated wastage through the combined affects of solar radiation and mechanical failure due to the rheological response of the ice to deepening kettle forms. Continuing degradation reduces the lake freeboard, weakens the moraine dam, and can lead to its catastrophic failure.
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Physical readjustments involved in glacier fluctuations present high risk situations at certain times and places. An outline of the history of glacier fluctuations in Holocene times and particularly the Little Ice Age provides the context for a discussion of the types of hazards associated with climatically led oscillations in populated areas and their timing. The threat from such glaciers has diminished but not disappeared with the recession of the last century. The impact of the more dramatic oscillations of surging glaciers and those with floating tongues has been limited by their restricted spatial distribution. Increased penetration of economic development into hitherto remote mountain regions and escalation of the numbers of people involved in sports such as skiing and mountaineering increase glacier hazard. Any future change in climate towards the conditions obtaining in the Little Ice Age would now involve greater risk from hazard than existed in former centuries. A more probable change in climate is rising temperature caused by more carbon dioxide in the atmosphere resulting in rising sea levels and perhaps surging of the Antarctic icesheet.