Recent (2004-2010) variations of surface displacements in an Andean permafrost-glacier environment (Chile, 33° S.) X. Bodin & G. F. Azócar Instituto de Geografía, Pontificia Universidad Católica de Chile, Santiago, Chile

A. Brenning Dep. of Geography and Environmental Management, University of Waterloo, Waterloo, Ontario, Canada

2 INTRA- AND INTERANNUAL KINEMATICS OF A TALUS ROCK GLACIER (2008-2010) The horizontal surface velocities measured on Punta Negra Bajo rock glacier range from 0.13 to 0.58 m/y, whereas the mean vertical displacement is -0.08 m/y (sd = 0.03). The part of the austral summer component (from Dec. 2008 to Apr.2009) in the total oblique displacement reaches on average 27-31% which, reported to a daily basis (taking account of the duration of the two measurement periods) yields 2 to 5 times more movement during austral winter (from Apr. 2009 to Jan. 2010) period. Furthermore, it appears that on average the ratio between vertical and horizontal movement is 4.7 at an annual timescale but reaches 9 during summer (and 4.4 during winter). 3 INTERANNUAL KINEMATICS OF A DEBRIS ROCK GLACIER AND A DEBRIS-COVERED GLACIER (2004-2010) The mean horizontal surface velocity on the debris rock glacier (lines A, B and C) of the Punta Negra Alto complex between (Fig. 1) April 2004 and April 2009 reached 0.32 m/y and the mean vertical dis-

0.8 0.6 0.4

0 A

B

C

D

A

B

C

D

0

B

C

B

C

Dec.08 - Apr.09

0.2

Apr.04 - Apr.09

Horizontal velocity [m/yr]

In the semi dry central Andes (Chile, 33° S.), glaciers, debris-covered glaciers and rock glaciers constitute the three main components of the cryosphere (except snow). Recent studies in the Laguna Negra area (Bodin et al., acc.) have shown, for the last 50 years, a shrinkage of uncovered glacier leading to an extension of debris-covered glacier area, frequently associated to thermokarst development. This works intends to present the main results of a 6-year GPS monitoring (measurements in Apr. 2004, Apr. 2009, Apr. 2010) of the annual ground surface displacement of a debris rock glacier and a debriscovered glacier and a 2-years GPS monitoring (measurements in Dec. 2008, Apr. 2009, Jan. 2010 and Apr. 2010) of seasonal surface displacement of a talus rock glacier.

placements -0.07 m /y. On the same period, the debris-covered glacier (line D) shows slightly higher horizontal velocities (0.48 m/y) but a clearly distinct vertical component (-0.16 m/y).

Vertical velocity [cm/yr]

1 INTRODUCTION

-10

-20

-30

Figure 1. Box-and-whiskler plot of the vertical and horizontal displacements (left box: annual; right: summer) of the ground on the 4 transverse lines of Punta Negra Alto complex.

4 DISCUSSION The high vertical velocities recorded on the debriscovered glacier are most probably related to the melting of the quasi-stagnant glacier ice covered by a thin debris mantle, as attested by the presence of numerous thermokarsts. The talus rock glacier combines winter horizontal velocity 1.1 times higher compared to summer with comparatively 1.5 times higher vertical velocity. Although the limited number of measurement dates impedes to have a good temporal resolution, such high vertical component in the total movement of the rock glacier might be due to a delayed thermal propagation of the summer heat wave associated to fusion of the ice-rich permafrost. Bodin, X., Rojas, F. & Brenning, A. accepted. State and recent evolution of the cryosphere in the Andes of Santiago (Chile, 33.5°S). Geomorphology, accepted.