Palcacocha Lake, Peru - Department of Civil, Architectural and

December 7, 2012
Term report: Glacial lake outburst flood
(GLOF). Palcacocha Lake, Peru.
Denny Rivas
A report prepared for the Geographic Information Systems course.
Environmental and Water Resources Engineering Program.
University of Texas at Austin.
1. Introduction
Palcacocha Lake in Peru is a tropical glacial lake
place. The failure makes water contained into the
subjected to Glacial Lake Outburst Flood (GLOF)
lake be suddenly released. The formed wave repre-
risk. Knowledge about the behavior of an expected
sents high risk for downstream population located
GLOF event in Palcacocha is required to identify
in the floodway.
emergency strategies to prevent human life losses
and major infrastructure damage in downstream
areas.
By using Geographic Information Systems (GIS)
and hydrodynamic modeling it is possible to asses
the flood evolution in time and space. The flood
Due to climate change, retreating of glaciers is
travel time from the lake to the downstream towns
increasing rapidly. As a consequence, glacial lakes
and its magnitude (extent, depth and velocity) can
volume is growing as the ice melts and increases
be determined combining both tools. The present
the deposited water volume. Among the hazards
analysis focus on designing a GLOF model based
derived from the lake changes, floods have cata-
on ArcGIS and Mike 11platforms applied to the
strophic effects on nearby areas life.
Palcacocha Lake case.
Such floods, commonly known as Glacial Lake
2. Study area
Outburst Flood (GLOF), are caused by a failure in
the natural dam (moraine) that holds lake water in
This report is focused on the Palcacocha Lake
region and its downstream areas, specially on Hua-
Study area
raz city, which is the main surrounding urban con-
indicated that by 2009 it has exceeded 17 millions
glomerate.
m3.
TABLE 1. Palcacocha Lake. Historical growing.
Year
Area (m2)
Volume (m3)
Max. Depth
(m)
1972
66,800
579,400
14
1974
62,800
514,800
13
2003
342,332
3,959,776
15
2009
518,426
17,325,207
73
The main risk concern about a GLOF event in Palcacocha is that Huaraz city is located 23km downFIGURE 1. Location map. Palcacocha Lake. Ancash
Region. Peru.
Palcacocha Lake is located at tropical latitudes in
the Southern hemisphere at 9º23’50”S and
77º22’54”W, at an elevation of 4567m. It belongs
stream from the lake. Cojup creek, whose origin is
Palcacocha, drains into Quilcay River, which flows
directly through Huaraz city before joining Santa
River.
to the Cordillera Blanca in Peru and it is fed by the
Historical catastrophic events precede current con-
Palcaraju glacier.
cerns about a new GLOF event in Palcacocha. In
Despite the tropical environment in which the glacier is immersed, elevations in andean mountains
are high enough to offer the climate conditions
required by a glacier to arise and subsist. However,
1941 the end moraine failed, causing a flood that
destroyed part of what was a small Huaraz city.
According to Carey (2010), 5000 people died
because 1941 flood.
such conditions are becoming hostile due to climate change. Growing of Palcacocha Lake volume
is an indicator of Palcaraju glacier melting and
retreating.
Palcacocha Lake changes have been documented
since 1972, indicating its volume is growing rapidly. In 1972 the volume was approximately 0.5
millions m3, while the last bathymetry measures
FIGURE 2. Huaraz city covered by the 1941 flood.
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
Pag. 2 of 8
GLOF modelling
In 1941 the lake volume was less than 12 million
to obtain a spatial and temporal representation of
m3. By 2010 it had already exceeded 17 million
the flood flow over a map.
m3. Otherwise, the critic volume has been estimated to be 0.5 million m3 (National Institute of
Civil Defense, 2011).
3.2. Terrain model
The modeling results can be just as accurate as the
Huaraz city has grown since 1941. It is now the
input data. The best available terrain information
capital of the Ancash region and its main touristic
from Palcacocha-Huaraz area is a 30m resolution
center. Its population has been estimated as
ASTER1
120,000 inhabitants (INEI, 2007). As the population and water volume has increased, the GLOF
hazard has become higher than it was in 1941.
Digital
Elevation
Model
(DEM).
Although partial LIDAR2 data was obtained, it
covers just a fraction of the Cojup Creek length to
be modeled.
3. GLOF modelling
3.1. Conceptual model
The adopted approach to reproduce a GLOF event
in Palcacocha Lake is based on the creation of a
terrain representation, over which hydraulic calculations are performed by a hydrodynamic model.
The results are produced and presented by the
interaction between both models. It is a preprocessing - processing and postprocessing approach.
FIGURE 3. Coverage of available Lidar data
The geometry inputs of the hydrodynamic model
are extracted from the terrain and the processed
results are overlapped on the same terrain in order
The magnitude of the event (flow depths of 10m
order are expected for peak discharges) reduces the
impact of low terrain accuracy on calculations over
1. Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) is a space mission launched by Japan and
United States agencies. Since 2011 the second version of the produced 30m DEM was released for public distribution.
2. Light Detection And Ranging (LIDAR) is an optical remote sensing technology. The gathered raw data did not contain the
required statistical measurements (average point distance) to process it. Such measurements were estimated by using GIS
tools.
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
Pag. 3 of 8
GLOF modelling
canyon shape intervals of the stream. However, on
ing hydrodynamic model. A constant interval
flat areas, the effect of terrain inaccuracy is
between sections of 90m has been used to extract
unavoidable.
the cross sections.
To estimate the order of magnitude of the 30m
DEM error in relation to high accuracy measurements, a new Digital terrain Model (DTM) has
been built using the LIDAR raw data.
The mean square deviation between them is
135.32m2, which suggests the error of the elevation
values of the 30m DEM is approximately  11.6m ,
which is high in relation to the expected depths
(around 10m), but less than the official reported
average accuracy of global ASTER DEM (15m).
Thus, the 30m DEM has been used as the terrain
model, taking into account the final results will be
FIGURE 4. Capture of the transect extraction interface
The final discrete terrain model is composed by a
24.6 km stream and 201 cross sections, which represents Cojup Creek, from Palcacocha Lake to
Huaraz city limits.
highly susceptible to depth errors.
One dimensional hydrodynamic models require to
transform raster represented DEM’s into discrete
transects distributed along the stream axis. The
transects and the stream axis has been extracted
from the DEM using a preprocessing plug-in for
ArcMap called MIKE-GIS1.
The distance between transects is set based on the
accuracy of the data, but also it is intended to be
short enough to provide a smooth transition
FIGURE 5. Cross sections extracted from the 30m
between cross sections. Such transition makes easy
ATER DEM.
to find a stable numerical solution for the upcom-
1. MIKE-GIS is the geospatial component of the MIKE 11 by DHI package used for hydrodynamic modelling.
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
Pag. 4 of 8
GLOF modelling
3.3. Hydrodynamic modeling
is uncertain how a breach would form and behave
on it. It will be assumed an overtopping failure, as
The hydrodynamic calculations were performed
suggested by Popov (1991), who proposed an
using MIKE 11, a one dimension unsteady state
empirical relation to estimate the expected maxi-
model. Three components are required to define a
mum flow for the GLOF as a function of the lake
GLOF process using such platform: lake volume,
volume. The characteristics of the breach, includ-
breach formation and the hydrodynamic parameters of the streamflow.
Lake volume. A bathymetric curve represents how
the lake volume changes as a function of elevation.
ing the time of formation, can then be adjusted to
approximate the peak of the modeled GLOF hydrograph (dam break model) to the Popov’s equation
maximum flow
Q max = 0.0048V
0.896
, where
3
Q max = maximum flow  m  s  and V = volume
3
of the lake  m  .
Using the bathymetry data, the maximum dis3
charge is 14 445m  s . The required formation
time of the breach shape shown in Figure 7, under
the established constraints, is approximately
30min.
FIGURE 6. Palcacocha Lake elevation - volume curve
Thus, it is related to the rate at which water will be
released as the dam breach grows. A curve
extracted from a bathymetry surface of Palcacocha
Lake (National Institute of Civil defense, 2009) is
shown in Figure 6.
FIGURE 7. Breach geometric characteristics
Hydrodynamic parameters. To gain numerical stability, the simulation time step has been set as 1
Breach formation. There is no much information
second and constant base flow of 200m  s has
about the moraine internal structure. It is known it
been introduced as initial condition. A simulation
is composed by debris, rock and ice deposits, but it
period of 4 hours covers the entire GLOF process,
3
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
Pag. 5 of 8
Results
since the breach failure until the lake volume has
The full time series raster is compressed by a mul-
been completely drained.
tiband file (dfs2 format), in which each band contains the results for each simulation time step.
The selected resistance flow expression is Manning’s equation. The applied n coefficient is 0.005
as recommended by Chow (1959) for mountain
rivers.
4. Results
Under the adopted dam breach formation hypothesis the arrival time of the flood to Huaraz urban
area is 22 minutes, while the peak downstream discharge (maximum flow) is produced 33 minutes
after the breach failure starts.
(a)
FIGURE 8. Huaraz city limits GLOF histogram
The water residence time, until the water is completely drained from the stream, is 70 minutes.
Spatial and temporal distribution of GLOF depth
(b)
and velocity are represented as time series surfaces
(rasters). Figure 9 shows water depth and velocity
FIGURE 9. GLOF stages at Huaraz city limits: (a)
at flood arrival time to Huaraz city limits.
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
flood depth at arrival time, and (b) flood
velocity at arrival time.
Pag. 6 of 8
Conclusions
Specific affected rural neighbors, located in the
As long as flat terrain is not reached, the model
floodway, are summarized in Figure 10 and Table .
produces stable results. When floodplain is
approached, before the junction of Cojup Creek
and Quilcay River, results are not longer reliable.
Therefore, model results are presented just for sections where they can be considered representative
of the actual flood.
The plain area of Huaraz could not be modeled.
However, the 1941 antecedent and the partial
results show the susceptibility of Huaraz city to a
GLOF event.
FIGURE 10. Maximum flood depth envelope and
affected rural towns
5. Conclusions
The lag time since the peak discharge leaves the
Although the applied approximations and inaccura-
moraine and arrives to the downstream areas is 18
cies around the proposed model affects the reliabil-
min. Therefore, the average GLOF wave celerity is
ity of the results, the order of magnitude of depth,
82km  h .
velocity and time is enough to asses the hazard into
TABLE 2. Flood arrival time and maximum velocities
which downstream communities are immersed.
in Huaraz inhabited areas
Towns
Arrival time
(min)
Max. Velocity
(m/s)
Capulipamba and Unchos
19
48.5
Cantu and Cantun
20
25
Huaraz Urban Area
22
20
According to the results, there is no enough available time (around 20 minutes) to perform an emergency evacuation plan once the GLOF has started.
Emergency structures (downstream engineered
The catastrophic damage of the 1941 GLOF is
dams) or reduction of the lake water volume are
explained by the estimated velocities. A 20 m/s (45
measurements might be considered as solutions to
mph) wave has enough power to knocks a person
reduce the GLOF hazard in Palcacocha Lake. Fea-
down even if it only comes up to the knees. A flood
sibility studies for each alternative should be sup-
of this nature gathers debris (trees, mud, rocks,
ported by models similar to the presented in this
etc.) and they create more destruction as they crash
report.
into other objects.
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
Pag. 7 of 8
References
To predict the impact of a GLOF in the urban core
Somos, M., & McKinney, D. C. (2011). Modeling
of Huaraz city, a two dimensions model is recom-
a glacial lake outburst flood (GLOF) from
mended to extent results to flat areas. Moreover,
Palcacocha Lake, Peru. Austin.
the current model exclusively reproduces water
flow, while the expected fluid is mostly a mixture
of mud, sediment and water (debris flow).
6. References
Bajracharya, B., Bhakta Shrestha, A., & Rajbhandari, L. (2007). Glacial Lake Outburst Floods
in the Sagamartha. Hazard Assesment Using
GIS and Hydrodynamic Modeling. Mountain
Research and Development, 27(4), 336-344.
Chow, V. T. (1959). Open Channel Hydraulics.
(Caldwell, Ed.). New Jersey: The Blackburn
Press.
Instituto Nacional de Defensa Civil. Peligro por
aluvión en el departamento de Ancash. Huaraz - Peru. Informe de Peligro No. 003-12/05/
2011/COEN-SINADECI/15:00 horas. (2011).
Lima.
Popov, N. (1991). Assesment of Glacial Debris
Flow Hazard in the North Tien Shan. Proceedings of the Soviet-China-Japan Symposium and Field Work on Natural Disasters
(pp. 384-391).
Silva, R. C. (2011). Procesos geodinámicos y peligros geológicos en los depósitos morrénicos
de la laguna de Palcacocha. Universidad
Nacional San Antonio Abad del Cusco.
Term report: Glacial lake outburst flood (GLOF). Palcacocha Lake, Peru.
Pag. 8 of 8
LOCATION MAP
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Palcacocha Lake. Ancash Region. Peru
Q. Y
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Calla c
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PALCACOCHA
LAKE
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Que rurec
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Akillpo 2
Glacier
Urus 2
Glacier
Tocllaraju 1
Glacier
Quebrada
Ishinca
Wallunaraju
Glacier
Ishinca 1
Glacier
Ishinca 2
Glacier
Llaca 1
Glacier
Llaca 2
Glacier
Carhuac 2
Glacier
Pacliash
Glacier
Tocllaraju 2
Glacier
Urayraju 2
Glacier
Janyaraju 2
Glacier
Palcacocha
Lake
Ranrapalca 2
Glacier
Ranrapalca 1
Glacier
Palcaraju
Glacier
Jatunmontepunku
Glacier
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Glacier
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Glacier
Shallap 1
Glacier
Q. p
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Cojup
Río
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Tararhua
Glacier
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Huantsan 2
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Sources: Esri, DeLorme,
NAVTEQ, TomTom, Intermap,
iPC, USGS, FAO, NPS,
NRCAN, GeoBase, IGN,
Kadaster
adaNL, Ordnance
Río altay
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Projection: Universal Transverse Mercator. Zone 16S
Datum WGS84
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Legend
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Que chua in
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Hydrography
Q. Santa
Catalina
8930000
Cities
"
6
220000
230000
DEM: Elevation (m)
RIVERS
2,100 - 2,600
LAKES
2,600 - 3,300
RIO SANTA
WATERSHED
3,300 - 3,600
CAPITALS
URBAN/RURAL
NEIGHBORHOODS
240000
3,600 - 4,600
< 6,743
Pucaraju
Glacier
TERRAIN DEFINITION
0
2
Palcacocha Lake. Ancash Region. Peru
Projection: Universal Transverse Mercator. Zone 16S
Datum WGS84
acu
Q. Y
u ra
Calla c
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Tocllaraju 2
Glacier
Ishinca 1
Glacier
Ishinca 2
Glacier
Urayraju 2
Glacier
Llaca 1
Glacier
Llaca 2
Glacier
Carhuac 2
Glacier
Pacliash
Glacier
Tocllaraju 1
Glacier
Quebrada
Ishinca
Wallunaraju
Glacier
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Glacier
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Glacier
Janyaraju 2
Glacier
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Glacier
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Glacier
Jatunmontepunku
Glacier
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Glacier
Cayesh 1
Glacier
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Cayesh 2
Glacier
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n
Shallap 1
Glacier
Q. p
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Sh
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Huantsan 2
Glacier
Huantsan 1
Glacier
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Legend
Hydrography
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LIDAR COVERAGE
LAKES
Q. Santa
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8930000
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6
230000
Terrain
CROSS SECTIONS
RIVERS
Cities
220000
Tararhua
Glacier
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Q.
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Río
S a n ta
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Pucaranra 2
Tullparaju
Glacier
Glacier
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HUARAZ
CITY
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Tullparaju
Glacier
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Glacier
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Glacier
Q.
Tr
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8950000
Queb
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Huell da
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Pucaranra
Glacier
Palcacocha
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Huamanripa 1
Glacier
Q. R
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Glacier
Urus 1
Glacier
Río shinca
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RIO SANTA
WATERSHED
CAPITALS
URBAN/RURAL
NEIGHBORHOODS
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DEM: Elevation (m)
2,100 - 2,600
2,600 - 3,300
3,300 - 3,600
3,600 - 4,600
< 6,743
Pucaraju
Glacier
GLOF MAXIMUM DEPTH
0
2
Palcacocha Lake. Ancash Region. Peru
Palcacocha
Lake
Projection: Universal Transverse Mercator. Zone 16S
Datum WGS84
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Q. Y
rad
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u
Q
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Ishinca 1
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Ishinca 2
Glacier
Urayraju 2
Glacier
Llaca 1
Glacier
Llaca 2
Glacier
Carhuac 2
Glacier
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Glacier
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Glacier
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Janyaraju 2
Glacier
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Glacier
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Glacier
Jatunmontepunku
Glacier
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Glacier
Cayesh 1
Glacier
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Callash
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Glacier
Q.
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Glacier
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Glacier
Río
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Glacier
Antonio
Raimondi
HUARAZ
CITY
Miyururi
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A tu
San
Francisco
Belén
Huaraz
Legend
Los
Pinos
La Soledad
Hydrography
Q. Santa
Catalina
Cities
8930000
"
6
220000
230000
GLOF Max. Depth (m)
RIVERS
0-3
LAKES
3-6
RIO SANTA
WATERSHED
9 - 12
CAPITALS
URBAN/RURAL
NEIGHBORHOODS
240000
6-9
12 - 16.8
Pucaraju
Glacier
GLOF MAXIMUM VELOCITY
0
2
Palcacocha Lake. Ancash Region. Peru
Palcacocha
Lake
Projection: Universal Transverse Mercator. Zone 16S
Datum WGS84
y
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Q. Y
rad
eb
u
Q
acu
Q. Y
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Wallunaraju
Glacier
da
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Q rure
ca
C ha
Ishinca 1
Glacier
Ishinca 2
Glacier
Urayraju 2
Glacier
Llaca 1
Glacier
Llaca 2
Glacier
Carhuac 2
Glacier
Pacliash
Glacier
Tocllaraju 2
Glacier
Qu
eb
Lla rada
ca
Río altay
P
Urus 2
Glacier
Quebrada
Ishinca
Janyaraju 2
Glacier
Palcacocha
Lake
Ranrapalca 2
Glacier
Ranrapalca 1
Glacier
Palcaraju
Glacier
Jatunmontepunku
Glacier
u re
a
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Q
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sc
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Yana
Tullparaju
Glacier
Quebrada
Callash
Q.
C
ca
Shallap 1
Glacier
Q. p
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Sh
rada
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Huantsan 2
Glacier
Huantsan 1
Glacier
ur
Q.
Tu
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Ruri
Uruashraju
Glacier
Río
S a n ta
lpa
Q. Co
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Micro
Pampa
Yanashallash
Glacier
Antonio
Raimondi
HUARAZ
CITY
Miyururi
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bra d
Que chua in
A tu
San
Francisco
Belén
Huaraz
Legend
Los
Pinos
La Soledad
Hydrography
RIVERS
Q. Santa
Catalina
Cities
8930000
"
6
220000
Tararhua
Glacier
Shacsha 1
Glacier
o
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Q cut
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Pu
Cayesh 1
Glacier
Cayesh 2
Glacier
Río
S a n ta
an
sha
n
Pucaranra 2
Tullparaju
Glacier
Glacier
Río
Quilcay
HUARAZ
CITY
8940000
Tullparaju
Glacier
Qu
eb
C a ra d
lca a
yh
ua
n
Churup 2
Glacier
Q.
Tr
an
ca
8950000
Queb
ra
Huell da
ap
crac
r
Pucaranra
Glacier
Ucro
Glacier
Huamanripa 1
Glacier
Q. R
a
o
Akillpo 1
Glacier
Urus 1
Glacier
Río shinca
I
8960000
il
qu
aA
Copap
Glacier
Akillpo 1
Glacier
Qu
e
Co b r a
jup da
a
ad a
br ond
e
Qu H
8 km
4
230000
GLOF Max. Vel. (m/s)
<10
LAKES
10-20
RIO SANTA
WATERSHED
30-40
CAPITALS
URBAN/RURAL
NEIGHBORHOODS
240000
20-30
<48.5
Pucaraju
Glacier