Jens Wendt

Ice volumetric changes on active volcanoes in southern Chile

Abstract Most of the glaciers in southern Chile have been retreating and shrinking during recent decades in response to atmospheric warming and decrease in precipitation. However, some glacier fluctuations are directly associated with the effusive and geothermal activity of ice-covered active volcanoes widely distributed in the region. The aim of this paper is to study the ice volumetric changes by comparing several topographic datasets. A maximum mean ice thinning rate of 0.81 ± 0.45 m a−1 was observed on the ash/debris-covered ablation area of Volcan Villarrica between 1961 and 2004, whilst on Volcan Mocho the signal-to-noise ratio was too small to yield any conclusion. An area reduction of 0.036 ±0.019 km2 a−1 since 1976 was obtained on Glaciar Mocho, while on Volcan Villarrica the area change was −0.090 ± 0.034 km2 a−1 between 1976 and 2005. Glaciers on active volcanoes are therefore shrinking, mainly in response to climatic driving factors. However, volcanic activity is affecting glaciers in two opposite ways: ash/debris advection is helping to reduce surface ablation at lower reaches by insulating the ice from solar radiation, while geothermal activity is probably enhancing melting and water production at the bedrock, resulting in negative ice-elevation changes.

Recent ice-surface-elevation changes of Fleming Glacier in response to the removal of the Wordie Ice Shelf, Antarctic Peninsula

Abstract Regional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

Airborne radar sounder for temperate ice: initial results from Patagonia

We describe the development of a low-frequency airborne radar specifically designed for the sounding of temperate ice. The system operates at a central frequency of 1MHz and consists of an impulse transmitter with an output voltage up to 5000V and a digital receiver with a maximum gain of 80dB. The radar was deployed on board a CASA 212 aircraft, which also carries a laser altimeter, an inertial navigation system, a digital camera and a GPS receiver. A description of the radar system is provided, as well as preliminary results obtained at Glaciar Tyndall, Campo de Hielo Sur (Southern Patagonia Icefield), where an ice depth of 670m was reached.

Reassessment of ice mass balance at Horseshoe Valley, Antarctica

Abstract Horseshoe Valley (80°18′S, 81°22′W) is a 30 km wide glaciated valley at the south-eastern end of Ellsworth Mountains draining into the Hercules inlet, Ronne Ice Shelf. The ice at Horseshoe Valley has been considered stable; now we use Global Positioning System (GPS) measurements obtained between 1996 and 2006 to investigate ice elevation change and mass balance. Comparison of surface heights on a profile across Horseshoe Valley reveals a slight but significant elevation increase of 0.04 m a-1 ± 0.002 m a-1. The blue ice area of Patriot Hills (∼13 km2) at the mount of Horseshoe Valley shows large interannual variability in area, with a maximum extent in 1997, an exceptionally warm summer, but no clear multi-year trend, and an elevation increase of 0.05 m a-1 in eight years, which agrees with the result from Horseshoe Valley.

The Patagonian ice fields: An updated assessment of sea level contribution

Climate Change: Global Risks, Challenges and Decisions IOP Conf. Series: Earth and Environmental Science 6 (2009) 012006 IOP Publishing doi:10.1088/1755-1307/6/1/012006 S01.06 The Patagonian ice fields: an updated assessment of sea level contribution Gino Casassa(1), W Krabill(2), A Rivera(0), J Wendt(1), A Wendt(1), P Lopez(1), F Bown(1), E Rignot(0), R Thomas(0), J Yungel(6), J Sonntag(6), E Frederick(6), R Russell(6), M Linkswiler(6), A Arendt(7), K Steffen(8) (1) CECS, Valdivia, Chile (2) Code 972, NASA-GSFC/WFF, Wallops Island, Virginia, USA (3) University of Chile, Santiago, Chile (4) School of Physical Sciences, University of California, Irvine, California, USA (5) JPL, Pasadena, California, USA (6) EG&G, NASA-GSFC/WFF, Wallops Island, Virginia, USA (7) Geophysical Institute, University of Alaska, Fairbanks, Alaska, U (8) CIRES, University of Colorado, Boulder, Colorado, USA The Northern and Southern Patagonia icefields (NPI and SPI) of southern South America have a total area of approximately 17,000 km 2 , constituting the largest temperate glacier system in the southern hemisphere. Snow precipitation can exceed 10 m/y water equivalent (w.e.) due to westerly air flow, with an important east-west gradient. In the lower reaches ablation can be larger than 10 m/y w.e., with abundant calving on fjords and freshwater lakes. The vast majority of the outlet glaciers show strong retreat and thinning in the ablation areas over the past century (Rignot et al., 2003), which can be largely explained by regional atmospheric warming. However, until now the data of the accumulation areas are insufficient for deriving the mass balance in the upper plateau. Here we compare new laser altimetry data of October 2008 with earlier data of November/December 2002 collected by airborne missions performed by NASA/CECS/Armada de Chile. The laser data are supplemented by the 2000 Shuttle Radar Topography Mission (SRTM) information and by 1975 and 1995 cartographic data of Chile. The data will allow to determine if thickening is occurring in the accumulation areas, as reported for example by Moeller et al. (2007) for Gran Campo Nevado, Patagonia, and if the rate of thinning at low elevations has experienced recent increases. As a result the contribution of the Patagonian icefields to sea level rise will be reassessed. c 2009 IOP Publishing Ltd