Takane Matsumoto

Satellite-derived equilibrium lines in Northern Patagonia Icefield, Chile, and their implications to glacier variations.

Abstract The Northern Patagonia Icefield (NPI), covering 3953 km2, is the second largest temperate ice body in South America. Despite its importance as a climate change indicator because of its location and size, data on ground-based mass balance and meteorological records for the analysis of glacier (snout) variations are still lacking. The use of multitemporal satellite images to estimate equilibrium line altitude variations could be a surrogate for such analyses. Since late-summer snowlines of temperate glaciers coincide with the equilibrium line, we analyzed five Landsat images spanning 1979–2003 and an ASTER-derived digital elevation model to reveal oscillations in the equilibrium line altitude (ΔZELA). The average ELAs range between 870 m and 1529 (± 29 m), with lower altitudes on the west side. Winter snow cover accumulation indicates higher elevations (relative to the glacier snout) of the transient snowlines in the west. Thus, one of the reasons for the higher retreating rates observed on the west side is that the lower part of the ablation area is likely exposed to year-round ablation. Glacier sensitivity to ΔZELA oscillations would depend upon the topographic condition of the accumulation area (gentle or steep). In outlet glaciers with gentle accumulation areas such as San Rafael and San Quintin, ΔZELA of up to 65 and 70 m at the central flow part and bare ice area variations > 5 km2 and > 13 (± 0.6 km2) were observed, respectively.

Surface Heat Balance and Spatially Distributed Ablation Modelling at Koryto Glacier, Kamchatka Peninsula, Russia

Abstract To investigate the characteristics of ablation at Koryto Glacier, a mountain glacier under maritime climate in Kamchatka Peninsula, Russia, we made field observations from August to early September 2000. At a site near the equilibrium line, the 31‐day average net radiation, sensible heat flux, and latent heat flux were 43, 59 and 31 W−2, respectively. We developed a new distributed ablation model, which only needs measurements of air temperature and global radiation at one site. Hourly ablation rates at this site obtained by the energy balance method are related to measured air temperature and global radiation by linear multiple regression. A different set of multiple regression coefficients is fitted for snow and ice surfaces. Better estimates of ablation rate can be obtained by this approach than by other temperature index models. These equations are then applied to each grid cell of a digital elevation model to estimate spatially distributed hourly melt. Air temperature is extrapolated using a constant temperature lapse rate and global radiation is distributed considering topographic effects. The model enables us to calculate the hourly spatial distribution of ablation rates within the glacier area and could well provide a realistic simulation of ablation over the whole glacier.

Multiday Variations in Flow Velocity at Glaciar Soler, Northern Patagonia, Chile

Abstract Ice flow speeds were measured at Glaciar Soler in northern Patagonia during the middle of the melt season (November–December) in 1998 and compared to data from 1985. In 1998 the surface flow speed was greater at all survey points, yet the ice was about 40 m thinner; the greater melt rate in 1998 probably explains these differences because of the effect of melt rate on basal sliding speed. Multiday variations in surface speed were well correlated with daily variations in surface water input, which is the sum of melt rate and rainfall. Although the basal sliding speeds vary from place to place, we obtained similar linear relationships between basal sliding speed and surface water input. This result indicates the possibility of taking account of basal sliding as a function of surface water input.

Summer Water Balance Characteristics of Koryto Glacier, Kamchatka Peninsula, Russia

Abstract The daily water balance for the drainage basin of Koryto Glacier, Kamchatka Peninsula, Russia, was calculated during the period from August to September 2000. The result shows that 14×106 m3 of meltwater and 2×106 m3 of rainwater entered the basin, while 26×106 m3 of water drained from the basin through proglacial streams. Thus, about −9×106 m3 of water storage reduction occurred in the basin. Vertical displacements of the glacier surface showed that the volume change due to contraction of subglacial cavities was nearly 20% of the total storage change. The remaining fraction of water storage during the period is thought to be stored in englacial and supraglacial locations. The estimate of water balance components in the early ablation season in 2000 indicates that meltwater was already stored within the glacier before the spring, even during the previous year, and that the stored water drained through the ablation season.

Influence of Debris Cover on Ogive-like Surface Morphology of Bilchenok Glacier in Kamchatka

ABSTRACT Bilchenok Glacier is a surging glacier in the Kamchatka Peninsula, Russia, which most recently surged in 1982 and is currently in its quiescent phase. Field research in 1998 revealed an ogive-like repeated pattern of transverse ridges and intervening gently sloping ice at the surface of the ablation area of this glacier. It was also observed that most of the glacial surface was covered by volcanic rocks and ash, and the debris thickness on the ridges was more than 1 m, whereas the gently sloping ice was covered by thin debris. We posit that the pattern of the debris thickness is caused by the unique conditions of Bilchenok Glacier, namely, the restricted position of its debris supply at the foot of the rock walls beside the icefall and its surging behavior. The distance between the ridges might indicate the total horizontal displacement attributable to surges. The dependence of the ablation rate on the debris thickness can result in a highly undulating ice surface between the ridge and the gently sloping ice. We estimate the effect of the debris thickness on the ice surface profile using a simple model and this model successfully predicts that high ice relief can be caused by different ablation rates in the debris cover thickness.