Snow Penitentes

JAVIER G. CORRIPIO1 AND ROSS S. PURVES2 1 Institute of Hydromechanics and Water Resources Management, ETH - Zürich, 2 Department of Geography, University of Zurich, Switzerland

3.1 INTRODUCTION

The Dry Central Andes stretching from latitude 31 °S to 35 °S are climatic deserts, yet they support rich agriculture and large urban centres thanks to melt water from glaciers and snow-covered mountains. Most of the agriculture of the Chilean Central Valley is irrigated (Schwerdtfeger 1976), and all drinking water for Santiago de Chile, with over five million inhabitants (one-third of the population of Chile), comes from water reservoirs fed by snow and ice melt during the summer. On the Argentinian side of the Andes, with barely 180 mm of annual precipitation, the provinces of Mendoza (population over 1.5 million) and San Juan are the country's main wine producers, and the region has rich agricultural farms. This production is only possible thanks to a well-developed irrigation system that makes efficient use of the summer melt water from the Cordillera. The contrast between the desert natural vegetation and the lush green of the cultivated farms is evident over the whole province, stressing the vital role of the mountains as ''water towers of the world for the 21st Century''. (Liniger etal. 1998)

In this paper, we present results from a field campaign and associated modelling, comparing the components of energy balance in this area with that ofAlpine basins and presenting low-cost remote sensing techniques suitable for use in a region where access is difficult and expensive. Particular attention is given to penitentes: surface ablation forms that are common on most glaciers of the Central Andes at high altitude and have an important effect on the energy and mass balance of the snow cover. The relative importance on snow ablation and therefore on water resources will be addressed.

3.2 SITE OF STUDY

The areas of study are two glaciers near the latitude of Santiago de Chile (see map in Figure 3.1): the Juncal Norte glacier near the border with Argentina and south of the Portillo pass, and the Loma Larga glacier on the headwaters of the Maipo river. The characteristics of the upper basins that contain the glaciers are summarised in Table 3.1. An automatic weather station (AWS) was installed on the snow surface and it collected data from 30 November to 11 December 2000 on Juncal and from 22 January to 24 February 2001 on Loma Larga. The instruments were carried with the help of local arrieros and mules from the nearest road to the base camp near the glacier snout and then by the researchers to the glacier location.

Climate and Hydrology in Mountain Areas. Edited by C. de Jong, D. Collins and R. Ranzi © 2005 John Wiley & Sons, Ltd

Figure 3.1 The area of study in the Chilean Andes, about 33°S 70°W. In the right upper photograph, Juncal Norte is the main glacier at the lower centre of the image, flowing north. Loma Larga is on the lower right corner of the lower image, in the opposite corner is the Yeso dam, the main water reservoir for Santiago de Chile. Map source: GLOBE project, NOAA, NGDC. Images from Aster: asterweb.jpl.nasa.gov. Courtesy NOAA

Figure 3.1 The area of study in the Chilean Andes, about 33°S 70°W. In the right upper photograph, Juncal Norte is the main glacier at the lower centre of the image, flowing north. Loma Larga is on the lower right corner of the lower image, in the opposite corner is the Yeso dam, the main water reservoir for Santiago de Chile. Map source: GLOBE project, NOAA, NGDC. Images from Aster: asterweb.jpl.nasa.gov. Courtesy NOAA

Table 3.1 Main characteristics of the upper catchment of the glaciers under study

Catchment 1 Catchment 2

Name of the basin

Juncal Norte

Loma Larga

Mountain range

Andes

Andes

Elevation range of upper catchment

2900-6100

2900-5404

Elevation range of individual sites

3335

4667

Latitude and longitude

32.98°S, 69.95°W

33.69°S, 70.00°W

Area in km2

21

18

% glacierised

39

66

Geology

Andesites, trachytes and

Andesites, trachytes and

basalts

basalts

Vegetation type (dominant)

Alpine xerophytic, desert

Alpine xerophytic, desert

Mean Q at catchment outlet

Unknown

Unknown

Mean hsun

3060 h

3220 h

0 0

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