1. The Andes of Peru are among the regions most
severely affected by glacier and high-mountain
hazards over the past 100 years. Very little is
known about high-mountain hazards in the
southern Peruvian Cordilleras of Cusco although
some of the largest debris flows worldwide
affected this region in recent years.
Here we analyze recent events in the Santa
Teresa region as part of a larger effort towards
an integrative risk management system.
Claudia Giráldez (1), Walter Choquevilca (2), Felipe Fernández (2), Holger Frey (1), Javier García (3), Wilfried Haeberli (1), Christian
Huggel (1), Sebastián Ludena (4), Mario Rohrer (5), and Wilson Suarez (6)
Large mass movements related to deglaciation effects in Southern Peru (Cusco)
(1) Department of Geography, University of Zurich, Switzerland (claudia.giraldez@geo.uzh.ch), (2) CARE-Perú, Lima y Cusco, Perú (3) Centre de Recherche sur
l’Environnement Alpin (CREALP), Sion, Switzerland, (4) Laboratoire de constructions hydrauliques, EPFL, Lausanne, Switzerland, (5) Meteodat GmbH, Zurich, Switzerland,
(6) Servicio Nacional de Meteorología e Hidrología del Perú (SENAMHI)
INTRODUCTION
Most mass movements causing disasters in
Santa Teresa originated in glaciated
catchments after periods of intense rainfall or
snow/ice melt. Sizes of these catchments are
between 100 and 300 km2, and the
corresponding glacier surface areas range
from 6 to 16 km2. The enormous February
1998 debris flow (ca. 25 million m3) that
destroyed the Machu Picchu hydropower
plant and buried the village of Santa Teresa
(now re-located, Fig.5 a) originated from a big
landslide after a period of high precipitation
(cumulative rainfall of the 40 days prior to the
event amounted to 170 mm), mobilized large
glacial-sediment reservoirs and temporarily
dammed the river Ahobamba causing very
high peak discharges. This pattern has been
recurrent in the area, e.g the January 1998
event in quebrada Sacsara (Fig. 2 and 3). The
most recent event occurred in January 2010
(Fig.5 b). Furthermore, a number of glacier
lakes underneath hanging glaciers and on
debris-covered dead-ice bodies (Figs 2 and 4)
can be found in all catchments. Their outburst
and release of large volumes of water can
induce a chain reaction of catastrophic
consequences. Therefore, monitoring and the
elaboration of a hazard and risk map of the
region is of crucial importance for prevention.
This work is a preliminary study of seven
communities of the district of Santa Teresa,
Cusco.
HAZARD SITUATION MAP AND OUTLOOK
The map here presented identifies the most
significant geomorphodynamic processes that
potentially may threaten the communities (see
Fig. 6 legend). It is not a standard hazard map but
rather a qualitative hazard-indication map
focusing only on populated areas. As shown,
major hazards consist of fast and slow landslides
(Santa Teresa, Sullucuyoc), marginal erosion of
the river and rockfall (Santa Rosa, Lucmabamba),
debris flows (quebradas draining to Vilcanota like
Ahobamba and Sacsara), and floods and
hyperconcentrated flows (along the river
Vilcanota). For other events on record, ongoing
fieldwork studies are carried out to analyze their
origin, trigger and characteristics. In order to
estimate the path, maximum flow height and
maximum velocity of potential hazardous events,
we carried out a model of debris flow through the
quebrada Ahobamba by using RAMMS (Fig.7).
Modeling was run for three scenarios with
different initial volumes. In combination with
fieldwork, model-based hazard mapping can be
very helpful. Taken together, the results suggest
that the area of Santa Teresa is highly vulnerable
and hard to analyze. The risks of damage to
infrastructure and houses are difficult to mitigate
and stress the importance of monitoring and land
use planning. Future work is oriented to improve
the risk map, to develop better event simulations,
to and develop a risk management system
together with the local communities.
ACKNOWLEDGEMENTS
Fig. 6 Hazard map for Santa Teresa District which identifies the most significant
geomorphodynamic processes that constitute a potential hazard for the most populated
communities. Google Earth photographs show the limit of the communities and are
labeled with potential hazards as described in the legend on the left. The central map
(30m ASTER GDEM2, color shaded relief) shows the situation of the different communities
along with the label of the hazards
Fig 7 Numerical modeling of maximum flow height for the quebrada Ahobamba
based on different magnitudes and return periods. The model used is RAMMS.
Initial volumes were, 200.000 m³, 1.000.000 m³ and 5.000.000 m³ for the small,
medium and large scenarios respectively. The corresponding return periods for the
three scenarios are ̴30 years, ̴100 years and ̴300 years. This model also calculates
the maximum flow velocity . Both results can be combined into an intensity map
and further into a preliminary hazard map. For this methodology see also
Hürlimann et al. (2008) and Schneider et al. (2012). (30m ASTER GDEM2, color
shaded relief)
We thank the Municipalidad de Santa Teresa and the communities of the
District for accompanying and supporting the field work and the different
initiatives. This study is part of the “Proyecto Glaciares 513” funded by SDC.
Fig.1 Situation map. Santa Teresa
(13⁰S; 72⁰W) is the capital of the
District, Povince of La Convención,
Department of Cusco.
Fig.4 Glacier lake Hanpi K´ocha under the hanging glaciers of
Nevado Pumasillo-Sacsarayoc in quebrada Sacsara. This lake has
almost no freeboard ( ̴5m) and its estimated volume might be
around 4.300.000m³.
Fig.2 Overview of quebrada Sacsara. Main potential hazards that
may originate in the upper parts of the quebradas: landslides, and
glacier-related hazards such as new lake formation and GLOFs.
(Landsat 5, 2010)
Fig.3 Starting zone of the 13th January
1998 landslide which mobilized large
glacier-sediment reservoirs after a
period of intense rainfall and formed a
large debris flow in quebrada Sacsara
that entirely destroyed the community
of Yanatile, now re-located (Fig. 6).
Fig.5 a New location of the
village of Santa Teresa since
1998 (old location signaled
in dotted brown circle). The
deposits of the 1998, and
2010, events cover the
riverbed of Río Vilcanota. b
Flood in Río Vilcanota
during the 2010 event.
Photo by C. Giráldez
Photo by C. Giráldez
Photo by C. Giráldez Photo by CARE
a b