Renji Naruse

Dynamic Features of Thinning and Retreating Glaciar Upsala, a Lacustrine Calving Glacier in Southern Patagonia

Glaciar Upsala, which calves into a lake on the eastern side of the Hielo Patagónico Sur, South America, has significantly retreated by 5 km during the last 20 yr. The glacier near the terminus has thinned by about 33 m from 1990 to 1993. Bathymetric surveys made in 1998 at the proglacial lake revealed the existence of bedrock rises spreading out from exposed islands in the western part of the lake. Between 1978 and 1990, the western half of the glacier terminus was located at the bedrock rises, which suggests that the front fluctuations were strongly controlled by the bed topography. During 1990–93, the glacier terminus was located upstream from the bedrock rises, and it is considered to have been floating after estimation of the buoyancy. Significantly large extending strain rate of 0.22 a−1 was deduced from the continuity consideration in 1990–93. These results are discussed with those obtained at Columbia Glacier, Alaska.

Calving rates in fresh water : new data from southern Patagonia

Abstract Data relating to calving dynamics in fresh water are scarce, especially for deep-water sites. A linear dependence of calving velocity (Vc) on water depth (Hw) is commonly accepted for both tidewater and fresh-water calving glaciers. Here we use recent data from temperate Patagonian glaciers to propose a revised relationship for calving in fresh water. The new ratio is derived from glaciers calving rapidly into deep water, documented using sequential satellite images and depth soundings. The main data source is a detailed remotely sensed dataset of the rapidly retreating Glaciar Upsala, complemented with global positioning system field surveys and precise ice-proximal bathymetric surveys. The area-integrated mean water depth between glacier positions in 1996 and 2000 is 490 m, with a maximum recorded depth of >700m. In the same period, image analysis reveals surface area loss of 1.37 km2 a–1 (4.8 km2) and an average calving rate of 1880ma–1. The resulting Vc/Hw ratio is of a similar order of magnitude to that recently derived for nearby Glaciar Moreno, but is well above the range of values commonly reported for lacustrine calving.

Current Knowledge of the Southern Patagonia Icefield

We present here a review of the current glaciological knowledge of the Southern Patagonia Icefield (SPI). With an area of 13,000 km2 and 48 major glaciers, the SPI is the largest ice mass in the Southern Hemisphere outside of Antarctica. The glacier inventory and recent glacier variations are presented, as well as ice thickness data and its variations, ice velocity, ablation, accumulation, hydrological characteristics, climate changes and implications for sea level rise. Most of the glaciers have been retreating, with a few in a state of equilibrium and advance. Glacier retreat is interpreted primarily as a response to regional atmospheric warming and to a lesser extent, to precipitation decrease observed during the last century in this region. The general retreat of SPI has resulted in an estimated contribution of 6% to the global rise in sea level due to melting of small glaciers and ice caps. Many glaciological characteristics of the SPI, in particular its mass balance, need to be determined more precisely.

Wind-Tunnel Experiments on Blowing Snow

Blowing snow was produced artificially in a cold wind-tunnel, and various measurements were conducted including particle diameters, concentrations, saltation lengths, heat transport and electric charge. The mean diameter of blowing snow particles decreased only slightly with increasing height; in the saltation layer, standard deviation was large and velocities were scattered in a wide range, suggesting the complex dynamic process on taking-off. The mean saltation length ranged from a few cm to 40 cm, increasing with wind velocity.

Dynamic behavior of Glaciar Perito Moreno, southern Patagonia

Frontal oscillations since the beginning of the 20th century are known at Glaciar Perito Moreno, an eastward outlet glacier of Hielo Patagonico Sur (southern Patagonia ice field). In 1900, the calving front was located about 1 km from the opposite bank. From 1935 to 1988, ruptures of ice-dams occurred at intervals of 1–5 years. Although this glacier has thus oscillated, it can be regarded as having been in a rather stable condition during the last half-century. Ice thickness in the ablation area has also remained unchanged from 1990 to 1996. The near-steady behavior of Glaciar Perito Moreno may be attributed to a regulating effect of the calving rate, namely, a decrease in the ablation amount due to calving with a retreat of the glacier. Using 12 m long ablation poles, ice-flow velocities at the ablation area were measured several times in 1993 and 1994. The velocity in the early summer (November) was found to be slightly larger than the annual mean. It is concluded that basal sliding is significant throughout the year at this temperate glacier, with large fluctuations within a short period.

Mass Balance Features Derived from a Firn Core at Hielo Patagónico Norte, South America

Glaciological research was carried out in November and December 1996 in the accumulation area of Glaciar Nef, an eastward-facing glacier from Hielo Patag6nico Norte (Northern Patagonia Icefield), South America. A 14.5-m-deep firn core (9.7 m water equivalent: w.e.) was obtained at 1500 m a.s.l., and air temperature and melting rate were also measured. Values of 8180 of 1or 2-cm-thick samples in the upper 6 m of the firn fluctuated from -16 to -10%o, which are explained by variations in 6880 of precipitation. Below 6 m in the firn, 8180 was almost constant, due to percolation of large amounts of meltwater. It was considered that the upper 6 m was deposited during the prior winter; thus winter balance in 1996 was derived as +3.5 m w.e. Based on the measurement results and

Short-term variations in flow velocity of Glaciar Soler, Patagonia, Chile

Short-term variations in ice-flow velocity were obtained at intervals of a few hours and a few days in the ablation area of Glaciar Soler, Patagonia, Chile, in November 1985. A maximum flow rate was measured at about four times the minimum value. A good correlation, with a time lag of 7.5 h, was found between the ice-flow velocity in the lower reaches and the amount of water discharge from the glacier terminus. It was concluded, therefore, that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure.

Climate reconstruction since the Little Ice Age by modelling Koryto glacier, Kamchatka Peninsula, Russia

Based on the field data at Koryto glacier, Kamchatka Peninsula, Russia, we constructed a one-dimensional numerical glacier model which fits the behaviour of the glacier. The analysis of meteorological data from the nearby station suggests that the recent rapid retreat of the glacier since the mid-20th century is likely to be due to a decrease in winter precipitation. Using the geographical data of the glacier terminus variations from 1711 to 1930, we reconstructed the fluctuation in the equilibrium- line altitude by means of the glacier model. With summer temperatures inferred from tree-ring data, the model suggests that the winter precipitation from the mid-19th to the early 20th century was about 10% less than that at present. This trend is close to consistent with ice-core results from the nearby ice cap in the central Kamchatka Peninsula.

Comparison of heat balance characteristics at five glaciers in the Southern Hemisphere

Abstract Ablation characteristics of five glaciers in Patagonia and New Zealand were compared. Investigated glaciers were Tyndall and Moreno in southern Patagonia, Soler and San Rafael in northern Patagonia, and Franz Josef in New Zealand. Micro-meteorological observations were carried out at the glaciers and the heat balance components were estimated. At Franz Josef and Soler glaciers, the sensible heat flux is the largest and the latent heat flux is the second, and they are larger than the net radiation. At San Rafael Glacier, the net radiation is the largest and the latent heat flux is the smallest component, which is similar to Moreno and Tyndall glaciers. Though the latent heat flux is the smallest component at San Rafael Glacier, it is more than twice as large as that at Tyndall Glacier and contributes substantially to ice melting. The ratios of heat balance components were very different among glaciers, but the total heat flux ranged from about 240 to 300 W m −2 showing little difference among glaciers.

Instruments and Methods: A novel backpackable ice-penetrating radar system

Abstract We have developed a novel ice-penetrating radar system that can be carried on a backpack. Including batteries for a 3 hour continuous measurement, the total weight is 13 kg. In addition, it operates reliably down to –25°C, has a low power consumption of 24 W, and is semi-waterproof. The system has a built-in-one controller with a high-brightness display for reading data quickly, a receiver with 12-bit digitizing, and a 1 kV pulse transmitter in which the pulse amplitude varies by <0.2%. Optical communications between components provides low-noise data acquisition and allows synchronizing of the pulse transmission with sampling. Measurements with the system revealed the 300 m deep bed topography of a temperate valley glacier in the late ablation season.