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Structure from motion and landslides: The 2010 Mt Meager collapse from slope deformation to debris avalanche deposit mapping

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  • Minerva Intelligence Inc.

Abstract and Figures

Structure from Motion (SfM) is a versatile photogrammetric tool that allows for rapid and high quality cartographic production. SfM can reconstruct the three-dimensional geometry of objects and surfaces in relative coordinates without the need for camera calibration parameters, or GCPs. Geometries and camera parameters can be retrieved during bundle adjustments from the redundancy of images. SfM can process newly acquired overlapping images as well as digitized historical vertical aerial photos. Measurements can be done with geographic coordinates or relative object coordinates without the need for precise GCPs. SfM is becoming a mature technology and a standard tool for geoscience and can be effectively applied to the study of historic landslides deformation to document ongoing motion or to map freshly emplaced deposits. The use of SfM in the detailed study of the 2010 Mt Meager landslide deposit, allowed a precise volume calculation and documentation of the slow deformation preceding the collapse. The 2010 Mt Meager landslide separated into a water-rich and a water-poor rheology phases with different run-out, characteristics and deposits. The slope prior the collapse was actively deforming and a glacier below the flank was retreating.
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20 Geotechnical News • June 2017 www.geotechnicalnews.com
GEOHAZARDS
Announcing
7th Canadian Geohazards
Conference – Geohazards 7:
Engineering Resiliency In A
Changing Climate
http://www.geohazards7.ca/
The Canadian Geotechnical Society
(CGS) is pleased to announce the 7th
Canadian Geohazards Conference –
Geohazards 7 – to be held June 3-6,
2018 at the Coast Canmore Hotel
& Conference Centre in Canmore,
Alberta. The CGS’s Geohazards
conferences are the premiere forums
in Canada for the sharing and dis-
semination of scientic and engineer-
ing knowledge related to geohazard
assessment and risk management.
Canmore is ideally situated for host-
ing Geohazards 7. It is located within
easy travel distance from the Calgary
International Airport, and is less than
a 30-minute drive from Banff National
Park. Heavy rainfall in June 2013
resulted in the worst oods in Alber-
ta’s history. Landslides, debris oods
and debris ows cut off highway and
rail access to Banff and Canmore, and
many homes constructed on allu-
vial fans were destroyed. Municipal
governments, the Province and the
engineering and geoscience commu-
nity have since carried out aggressive
programs to quantify geohazard risk,
increase public awareness of hazards,
and are constructing mitigation mea-
sures to reduce future risk. Canmore is
a terric venue to showcase the results
of some of these initiatives, which will
feature in the conference program and
eldtrip.
This conference will be of interest to
engineering and geoscience students
and consultants, industry, and gov-
ernment agency representatives who
are involved in planning, approval,
construction and operation of infra-
structure and residential develop-
ment in areas prone to geohazards.
The conference will touch on the full
gamut of hazards and risks associated
with oods, debris ows, landslides,
snow avalanche, earthquakes, volcanic
eruptions, degrading permafrost and
more. Arming participants with greater
awareness of methods for quantifying
geohazard magnitude and frequency
for risk assessment and mitigation
design, quantifying uncertainty in a
changing climate, and communicat-
ing with the public about geohazard
issues, are key objectives of the
conference.
Closing Notes
If you have a paper or project related
to Geohazards that you think would be
interesting to GN readers, please send
me note at Richard.Guthrie@stantec.
com. Have a safe and productive eld
season. We’ll see you in September.
Structure from motion and landslides:
The 2010 Mt Meager collapse from slope deformation
to debris avalanche deposit mapping
Gioachino Roberti, Brent Ward, Benjamin Van Wyk de Vries, Luigi Perotti
Topographic reconstruction is a funda-
mental operation in geotechnical and
geomorphological studies. In recent
years, three-dimensional surface
reconstruction has been revolutionized
by the development of Structure from
Motion (SfM) photogrammetry. The
SfM technique allows rapid base map
production from any set of overlap-
ping photographs. Surface information
can be retrieved from these images
without the need of camera calibra-
tion, ground control points, or any
other external information.
We present herein, the application of
SfM to the study of the 2010 Mount
Meager debris avalanche. We used
SfM to produce base maps for a large
scale (1:1000) geomorphic study
of the debris avalanche deposit, to
produce a post-event DEM of the
collapse scar and generate sequential
DEMs to track the deformation of the
Mt Meager ank pre-collapse. In the
www.geotechnicalnews.com Geotechnical News • June 2017 21
GEOHAZARDS
study of the deposit and the collapse
scar we processed oblique helicopter
digital photos taken with a standard
SLR camera. For the observations of
the ank prior to the collapse, we used
digitized historical vertical aerial pho-
tos. We processed both oblique photos
and vertical historical aerial photos
with the commercial SfM software
package PhotoScan. SfM is a powerful
tool for geologists and geomorpholo-
gists and quickly becoming standard
technique in interpretive geoscience.
Structure from Motion
Originally, Structure from Motion
(SfM) refers to the computing vision
problem of reconstructing the geom-
etry of an object (Structure) from a
moving sensor (Motion). With the
use of SfM, the three-dimensional
geometry of scenes and objects can
be retrieved from sequential two-
dimensional images by measuring
geometric differences between images.
In geoscience, SfM refers to a com-
posite workow of Structure from
Motion and Multi View Stereo (MVS)
algorithms. The SfM process matches
features between images, estimates
the camera position and parameters,
and delivers a sparse point cloud in
generic x, y, z object coordinates. The
MVS increases the number of matches
to generate a denser point cloud. The
point cloud can be then georeferenced
by adding ground control points
(GCP) and interpolated to generate
digital elevation models (DEM).
The use of SfM does not require
specialized personnel or expensive
software, making three-dimensional
modelling accessible to everyone. This
technique is broadly applied from the
hand-sample reconstruction to outcrop
modelling and medium scale topogra-
phy generation. SfM-derived DEMs
have been proven to be of comparable
quality to Lidar DEMs. While SfM is
most often used with imagery taken
from a hand-held camera or unmanned
aircraft vehicles (UAV)few studies
have explored the application with his-
torical aerial photos. Limitations exist
related to the automated workow
where errors are difcult to identify
and control, however, recent work has
focused on assessing and reducing
such errors allowing broader accep-
tance of SfM
SfM allows for a rapid and high-
resolution cartographic production
effective in the assessment of natural
disasters. For landslides it can be used
to generate post-event topography, to
get sequential DEMs of slow moving
landslides, or to perform kinematic
analysis of joints and discontinuity
sets.
There are many open source and
commercial SfM packages available.
We used PhotoScan to reconstruct the
2010 Mt Meager landslide deposit,
landslide scar and the slope distress of
the ank prior to the collapse. Photo-
scan includes, in a single package, the
whole workow from image match-
ing to orthophoto and DEM extrac-
tion, allowing point cloud and mesh
editing. Its efciency, straightforward
workow, and a user-friendly interface
has made Photoscan successful with
a wide scientic literature to prove its
reliability and precision.
The 2010 Mt Meager landslide
In 2010 the south ank of Mt Meager
(British Columbia, Canada) failed
catastrophically (Figure 1) generat-
ing the largest (~50 Mm3) landslide
in Canadian history (Guthrie et al.,
2012). The collapse evolved as four
structurally controlled sub-failures that
retrogressed from the base of the ank
to the peak of the mountain (Roberti et
al., in press.). The rock mass fractured
forming a rapid debris avalanche that
reached peak velocity of 90 m/s, ran
up to 270 m on the valley sides and
travelled 12.7 km damming Capricorn
Creek for 19 h and partially damming
Lillooet River for 2 h.
SfM-derived base maps were used
for detailed descriptions of the
deposit and revealing the separation
of a water-rich frontal debris ow
and a water-poor, less mobile debris
avalanche core in the landslide event.
The SfM analysis of historical aerial
photos over Meager Peak allowed
the description of the ongoing slow
deformation on the ank responding to
glacier pulsations at its base. We cal-
culated the volume of the collapse and
the geometry of the sub-failures by
Figure 1. Photograph of the main collapse of Mt Meager. Note helicopter for
scale (photograph courtesy of R. Guthrie).
22 Geotechnical News • June 2017 www.geotechnicalnews.com
GEOHAZARDS
comparing the 2006 and the post-event
DEMs. Glacial retreat in the years
preceding the collapse, in addition
to faulting, deformation, and smaller
failures, were all evident in the lower
ank from SfM analysis.
Details of the volume and mechan-
ics of the 2010 Mt Meager landslide
are expected to be released shortly
in an upcoming paper in Landslides
(Roberti et al., in press). At this point
we can say that we improved on the
original volume estimate of Guthrie, et
al. (2012), that the landslide is some-
what larger than previously supposed,
and that, using SfM, we were able
to make a more precise description
of both causal mechanisms and the
mechanics of the collapse.
2010 debris avalanche deposit
For the geomorphological study of
the 2010 Mt Meager landslide deposit
we took pictures from a low-level
helicopter traverse with a digital
Canon SLR camera. We processed 712
images, where poor quality images
were excluded (blurred, overexposed)
and, when necessary, the helicopter
skids masked out. The resulting ortho-
photo and DEM have a resolution of
8 cm/pixel and 0.34 m/pixel (point
density at 0.64 pts/sq m), respec-
tively. GCP planimetric coordinates
were retrieved from a 0.5 m GeoEye
orthophoto while vertical information
was from a 25 m resolution British
Columbia Terrain Resource Inventory
Mapping (TRIM) DEM of 18.3 m
average accuracy.
The precise distribution of different
debris avalanche facies was mapped
at 1:1000 scale (Figure 2) and depos-
its related to different water contents
phases were recognized (Roberti et al.,
2017). The deposits were correlated
water-rich and water-poor phases. The
water-rich phase superelevated and left
relatively thin scattered distal deposits.
The water-poor phase was conned to
the valley bottom and stopped rapidly
leaving thick hummocky deposits.
1948-2006: The deformation before
the collapse
We documented more than a half-cen-
tury of geomorphological evolution
of the south ank of Mt Meager from
historical aerial photos, orthophotos
and DEMs. A rich archive of histori-
cal vertical aerial photos is available
at the Geography Department Library
at UBC (University of British Colum-
bia). The study area was captured in
1948, 1964, 1973, 1981, 1990, 2006.
We digitized the aerial photos and
processed them with PhotoScan to
reconstruct the diachronic evolution of
the three-dimensional geometry of the
ank. The frames were scanned at 800
dpi with a standard A3 scanner, orient-
ing the strip ight direction parallel
to the CCD array of the scanner. To
georeference the models, planimet-
ric coordinates were retrieved from
SPOT-10 m resolution imagery while
the vertical information was obtained
from the 25 m BC TRIM DEM.
To test the precision of the carto-
graphic products, we took control
points from a Lidar DEM acquired
during summer of 2015. The 2006
and the post-collapse DEMs were
compared using a pixel-wise differ-
ence, and calculating the volume of
the failed mass. It was also possible to
calculate the volume and the geom-
etry of the sub-failures, interpolating
the supercial faults between the two
DEMs. The error in the volume calcu-
lation was assessed by comparing the
two surfaces outside of the collapse
scar, where no change was expected
and calculating the same relative error
for the volume estimate.
In addition, we mapped the extent
of the glacier tongue at the base of
the failed slope on each orthophoto.
Uncertainties in this exercise related to
inherent errors in the base map, to the
manual tracing of the glacier perim-
eter, and difculty of distinguishing
between ice, snow and snow-covered
ice. We used the inherent pixel preci-
sion of the orthophotos to buffer the
perimeter of the glaciers. The preci-
sion of the glacier area was calculated
as the root of the squared sum of the
buffered areas.
An interpretation of the 2006 topogra-
phy is shown in Figure 3.
Figure 2. Detail of the 2010 Mt Meager debris avalanche deposit. High reso-
lution mapping allowed the identication of different stress regimes: exten-
sion (light blue) at the west corner; shear (purple) in the central part and at
the sides; and compression (red) at the front and between the two lobes.
Modied from (Roberti et al., 2017).
www.geotechnicalnews.com Geotechnical News • June 2017 23
GEOHAZARDS
Figure 3. SfM-derived 3D view of Mt Meager before the 2010 collapse. Frac-
tures are evidenced: they indicate active deformation of the slope prior the
collapse. Modied from (Delcamp et al., 2016).
Georeferencing and cartography
accuracy
The standard procedure in georefer-
encing digital geospatial data is to
use coordinates from a source with
higher accuracy. Commonly, GCP
coordinates are measured in the eld
during a differential GNSS survey. In
our case, it was not feasible to acquire
GNSS points in the eld and the coor-
dinates used for georeferencing the
SfM models were retrieved from the
available Canada imagery and DEMs.
The accuracy of the coordinates used
(10 m planimetric and 18.3 m verti-
cal) in the georeferencing process
was lower than the potential accuracy
of the SfM products (0.8 cm for the
deposit images and 0.5 m -1 m for the
historic photos). The pixel precision
of the models depends on the photo
quality, the original images pixel size
and the matching algorithm. The nal
cartographic accuracy depends on the
geographic/cartographic coordinate
source used in the georeferencing
process. During georeferencing other
errors might be introduced when
GCPs have lower accuracy than the
three-dimensional matching. When
the GCPs have higher accuracy than
the bundle adjustment, they might
improve the model quality. When
GCPs are lacking and/or they are not
reliable, the models might be just
scaled for relative volume and area
calculations.
The ability of SfM to build three-
dimensional geometries with relative
object coordinates gives the user the
opportunity of making quick maps
that do not necessarily require GCP
surveys. Observations can be done in
relatively-scaled object-coordinates
without ground control. Careful evalu-
ation of the models is nevertheless
required, especially when GCPs are
not used, to reduce erroneous recon-
structed areas and wrongly projected
points.
Summary
Structure from Motion (SfM) is a
versatile photogrammetric tool that
allows for rapid and high quality
cartographic production. SfM can
reconstruct the three-dimensional
geometry of objects and surfaces in
relative coordinates without the need
for camera calibration parameters,
or GCPs. Geometries and camera
parameters can be retrieved during
bundle adjustments from the redun-
dancy of images. SfM can process
newly acquired overlapping images
as well as digitized historical vertical
aerial photos. Measurements can be
done with geographic coordinates or
relative object coordinates without
the need for precise GCPs. SfM is
becoming a mature technology and a
standard tool for geoscience and can
be effectively applied to the study
of historic landslides deformation to
document ongoing motion or to map
freshly emplaced deposits.
The use of SfM in the detailed study
of the 2010 Mt Meager landslide
deposit, allowed a precise volume
calculation and documentation of
the slow deformation preceding the
collapse. The 2010 Mt Meager land-
slide separated into a water-rich and
a water-poor rheology phases with
different run-out, characteristics and
deposits. The slope prior the collapse
was actively deforming and a glacier
below the ank was retreating.
References
Delcamp, A., Roberti, G., van Wyk de
Vries, B., 2016. Water in volca-
noes: evolution, storage and rapid
release during landslides. Bull.
Volcanol. 78, 87. doi:10.1007/
s00445-016-1082-8
Guthrie, R.H., Friele, P., Allstadt, K.,
Roberts, N., Evans, S.G., Delaney,
K.B., Roche, D., Clague, J.J.,
2012. The 6 August 2010 Mount
Meager rock slide-debris ow ,
Coast Mountains , British Colum-
bia : characteristics , dynamics ,
and implications for hazard and
risk assessment 1–18. doi:10.5194/
nhess-12-1-2012
Roberti, G., Friele, P., van Wyk de
Vries, B., Ward, B., Clague,
J.J., Perotti, L., Giardino, M.,
2017. Rheological evolution of
the Mount Meager 2010 debris
avalanche, southwestern Brit-
ish Columbia. Geosphere 13,
GES01389.1. doi:10.1130/
GES01389.1
Roberti, G., Ward, B., van Wyk de
Vries, B., Friele, P.A., Perotti,
L., Clague, J.J., Giardino, M., in
press. Precursor slope distress
leading up to the 2010 Mount
24 Geotechnical News • June 2017 www.geotechnicalnews.com
GEOHAZARDS
Meager landslide, British Colum-
bia. Landslides.
Gioachino Roberti
Earth Sciences Department, Simon
Fraser University, 8888 University
Drive, Burnaby, British Columbia
V5A 1S6, Canada, groberti@sfu.ca
Brent Ward
Earth Sciences Department, Simon
Fraser University, 8888 University
Drive, Burnaby, British Columbia
V5A 1S6, Canada.
Benjamin Van Wyk de Vries
Université Clermont Auvergne,
CNRS, IRD, OPGC, Laboratoire
Magmas et Volcans, F-63000,
Clermont-Ferrand, France.
Luigi Perotti
Earth Sciences Department,
University of Torino, Via Valperga
Caluso 35, 10125 Torino, Italy.
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CFEM June 2014 Ad.indd 1 14-05-20 10:18 AM
... SfM is generally applied to photographs taken with a hand-held camera or from an Unmanned Aircraft Vehicle (UAV) (James and Robson 2012). In comparison, few studies have explored the application of Structure from Motion (SfM) to digitized historical vertical aerial photographs (Gomez et al. 2015;Bakker and Lane 2016;Roberti et al. 2017b). In this study we processed 114 British Columbia Government vertical aerial photographs acquired in the summer of 2006 (see Roberti et al. 2017c for details on data processing). ...
Thesis
Full-text available
Mount Meager is a glacier-clad volcanic complex in British Columbia, Canada. It is known for its landslides, of which the 2010 is the largest Canadian historical landslide. In this thesis we investigated slope instability processes at Mount Meager volcano and the effects of ongoing deglaciation. We used a variety of methods including field and remote, geological, geomorphological and structural mapping to characterize glacial and landslide activity at Mount Meager. We used Structure from Motion photogrammetry (SfM) and Lidar to produce digital surface models and InSAR to monitor slope deformation. We applied SfM to historic photography to document glacier and landslide activity at Mount Meager. We discussed a model of growth and erosion of a volcano in glacial and interglacial periods, and the scientific and dissemination value of historic 3D topographic reconstruction. We described the 2010 Mount Meager landslide deposit to interpret emplacement dynamics and kinematics. The 2010 landslide separated in water-rich and water-poor phases that had different runout and distinct deposits. We analyzed historic airphotos to constrain the slope deformation prior to the 2010 collapse. The glacier near the toe of the slope retreated in the failure lead up, the collapse evolved in four subfailures involving the whole volcanic sequence and some basement rocks. We estimated 6 × 106 m3 of water in the slope, that allowed the separation of the frontal water-rich phase. The total failure volume was 53 ± 3.8 × 106 m3. We identified 27 large (>5×105 m2) unstable slopes at Mount Meager and calculated ~1.3 km3 of ice loss since 1987. The west flank of Plinth peak and Devastation Creek valley moved up to -34±10 mm and -36±10 mm, respectively, over a 24-day period during the summer of 2016. The failure of these slopes could impact infrastructures and communities downstream of the volcano. The resulting decompression on the volcanic edifice after the failure of Plinth peak would affect the stress field to a depth of 6 km and up to 4 MPa. This sudden decompression could lead to hydrothermal or magmatic eruptions.
... SfM is generally applied to photographs taken with a hand-held camera or from an Unmanned Aircraft Vehicle (UAV) (James and Robson 2012). In comparison, few studies have explored the application of Structure from Motion (SfM) to digitized historical vertical aerial photographs (Gomez et al. 2015;Bakker and Lane 2016;Roberti et al. 2017b). In this study we processed 114 British Columbia Government vertical aerial photographs acquired in the summer of 2006 (see Roberti et al. 2017c for details on data processing). ...
Conference Paper
Full-text available
Mt. Meager is a glacier-clad volcanic complex in southwest British Columbia. In the summer of 2010, melting snow and ice caused by warm weather triggered the collapse of 53 Mm 3 of rock and debris from Mt. Meager's south flank, generating the largest historic landslide in Canada. In 2016 fumaroles formed ice caves in one of its glaciers, raising concern about the potential for eruptive activity. Following these events, we carried out a geomorphic study of the volcano. Employing satellite-based differencing methods, we measured movements on previously identified unstable slopes and documented the recent retreat of glaciers on the volcanic complex. It is likely that glaciers will continue to thin and recede, and that slopes will continue to deform, possibly leading to catastrophic collapses similar to the 2010 event. Previous work concluded that the level of risk posed by large landslides at Mt. Meager is unacceptable. In spite of this conclusion, little has been done to manage the risk by local or provincial governments over the past decade. With new hydropower infrastructure near the volcano and continued population growth in the Lillooet River valley downstream, it is clear that the landslide risk is increasing.
Article
Full-text available
Volcanoes can store and drain water that is used as a valuable resource by populations living on their slopes. The water drainage and storage pattern depend on the volcano lithologies and structure, as well as the geological and hydrometric settings. The drainage and storage pattern will change according to the hydrometric conditions, the vegetation cover, the eruptive activity and the long- and short-term volcano deformation. Inspired by our field observations and based on geology and structure of volcanic edifices, on hydrogeological studies, and modelling of water flow in opening fractures, we develop a model of water storage and drainage linked with volcano evolution. This paper offers a first-order general model of water evolution in volcanoes.
Article
Full-text available
A large rock avalanche occurred at 03:27:30 PDT, 6 August 2010, in the Mount Meager Volcanic Complex southwest British Columbia. The landslide initiated as a rock slide in Pleistocene rhyodacitic volcanic rock with the collapse of the secondary peak of Mount Meager. The detached rock mass impacted the volcano's weathered and saturated flanks, creating a visible seismic signature on nearby seismographs. Undrained loading of the sloping flank caused the immediate and extremely rapid evacuation of the entire flank with a strong horizontal force, as the rock slide transformed into a debris flow. The disintegrating mass travelled down Capricorn Creek at an average velocity of 64 m s-1, exhibiting dramatic super-elevation in bends to the intersection of Meager Creek, 7.8 km from the source. At Meager Creek the debris impacted the south side of Meager valley, causing a runup of 270 m above the valley floor and the deflection of the landslide debris both upstream (for 3.7 km) and downstream into the Lillooet River valley (for 4.9 km), where it blocked the Lillooet River river for a couple of hours, approximately 10 km from the landslide source. Deposition at the Capricorn-Meager confluence also dammed Meager Creek for about 19 h creating a lake 1.5 km long. The overtopping of the dam and the predicted outburst flood was the basis for a night time evacuation of 1500 residents in the town of Pemberton, 65 km downstream. High-resolution GeoEye satellite imagery obtained on 16 October 2010 was used to create a post-event digital elevation model. Comparing pre- and post-event topography we estimate the volume of the initial displaced mass from the flank of Mount Meager to be 48.5 × 106 m3, the height of the path (H) to be 2183 m and the total length of the path (L) to be 12.7 km. This yields H/L = 0.172 and a fahrböschung (travel angle) of 9.75°. The movement was recorded on seismographs in British Columbia and Washington State with the initial impact, the debris flow travelling through bends in Capricorn Creek, and the impact with Meager Creek are all evident on a number of seismograms. The landslide had a seismic trace equivalent to a M = 2.6 earthquake. Velocities and dynamics of the movement were simulated using DAN-W. The 2010 event is the third major landslide in the Capricorn Creek watershed since 1998 and the fifth large-scale mass flow in the Meager Creek watershed since 1930. No lives were lost in the event, but despite its relatively remote location direct costs of the 2010 landslide are estimated to be in the order of 10 M CAD.
Article
On 6 August 2010, a large (-50 Mm3) debris avalanche occurred on the flank of Mount Meager in the southern Coast Mountains of British Columbia, Canada. We studied the deposits to infer the morphodynamics of the landslide from initiation to emplacement. Structure from motion (SfM) photogrammetry, based on oblique photos taken with a standard SLR camera during a low helicopter traverse, was used to create high-resolution orthophotos and base maps. Interpretation of the images and maps allowed us to recognize two main rheological phases in the debris avalanche. Just below the source area, in the valley of Capricorn Creek, the landslide separated into two phases, one water-rich and more mobile, and the other water-poor and less mobile. The water-rich phase spread quickly, achieved high superelevation on the valley sides, and left distal scattered deposits. The main water-poor phase moved more slowly, did not superelevate, and formed a thick continuous deposit (up to -30 m) on the valley floor. The water-poor flow deposit has structural features such as hummocks, brittle-ductile faults, and shear zones. Our study, based on a freshly emplaced deposit, advances understanding of large mass movements by showing that a single landslide can develop multiple rheology phases with different behaviors. Rheological evolution and separation of phases should always be taken into account to provide better risk assessment scenarios.