Masamu Aniya

Holocene Glacial Chronology in Patagonia: Tyndall and Upsala Glaciers

From glacial landforms and new radiocarbon datings at Tyndall and Upsala Glacier areas of the Southern Patagonia Icefield, four Neoglacial advances are recognized. At Tyndall Glacier, a First Neoglacial advance, marked by obscure terminal moraines and distinctive lateral moraines occurred at ca. 3600 yr BR A Second Neoglacial advance, indicated by conspicuous trimlines on the side-valley wall and on the flank of the lateral moraines of the First Neoglacial advance, presumably occurred at ca. 2300 yr BP A Third Neoglacial advance, distinguished by the different color and surficial materials of the terrain, occurred at ca. 1400 yr BR A Fourth Neoglacial advance occurred at ca. A.D. 1700. At Upsala Glacier, a new scheme was presented, modifying the classical scheme of Mercer. He identified two Neoglaciations from radiocarbon datings at ca. 3600 yr BP, and ca. 2300 yr BP (Pearson I), and the Little Ice Age glaciation, Pearson II, at A.D. 1600-1760 from dendrochronological analyses. In this study, Herminita moraines that were first recognized in 1990 were dated to be ca. 24002200 yr BP, corresponding to a Second Neoglaciation. Pearson I moraines which were long believed to be ca. 2300 yr BP were dated to be ca. 1600, 1400, and 900 yr BP These dates are close to a Third Neoglaciation. The existence of the earliest Neoglaciation, ca. 3600 yr BP, was not directly supported by new data; however, the data from Tyndall and other glaciers suggest that it probably occurred at Upsala Glacier.

GLACIER INVENTORY FOR THE NORTHERN PATAGONIA ICEFIELD, CHILE, AND VARIATIONS 1944/45 TO 1985/86

The 28 outlet glaciers of the Northern Patagonia Icefield, Chile, with a total contiguous surface area of about 4200 km2, were inventoried in a detailed statistical manner. The San Quintin and San Rafael glaciers, each with an area of about 760 km2, are the two largest. Equilibrium lines are estimated at elevations of 900 to 1350 m, separating the total area into an accumulation area of 2578 km2 and an ablation area of 1550 km2.The variation of 22 major glaciers between 1944/45 and 1985/86 was elucidated and an annual average rate of recession of up to 68 m yr–1 was determined. One glacier showed almost no change at all, while the southwestern snout of the Reicher Glacier showed a net advance, although small. A decrease in accumulation in the icefield has caused this general recession. However, the individual variation was probably governed by one of or a combination of the following four factors: (1) orographic situation of the accumulation area, i.e., whether it is located on the leeward (eastern) or wi...

Glacier Variations and Their Causes in the Northern Patagonia Icefield, Chile, Since 1944

The variations of six outlet glaciers of the northern Patagonia icefield were investigated. utilizing aerial photographs taken in 1944/45, 1974/75, and 1983/84, and were compared with the climatic trend. Between 1944 and 1984, a maximum recession of around 2.5 km was observed at two calving glaciers, while no variation occurred at one glacier. Three patterns of variations were recognized: (1) fairly constant recession during the last 40 yr (two glaciers); (2) rapid retreat during the 1974-1984 period (two glaciers); and (3) rapid retreat between 1944 and 1958. The amount of the surface lowering ranges from 40 to 120 m during the last 40 yr. These retreat and surface lowering rates are generally comparable to those reported for glaciers in other regions. The temperature and precipitation data recorded at a nearby station do not show any definite trends which can explain the general glacier variations elucidated in this study, suggesting strong local variation of the snow accumulation and effect of the relative height of the rock threshold on ice spilling.

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.

Hybrid classification of Landsat data and GIS for land use/cover change analysis of the Bindura district, Zimbabwe

Rapid land use/cover changes have taken place in many parts of Zimbabwe, including the Bindura district, mainly due to unequal land distribution during the colonial period, demographic pressure, agricultural expansion, government policies and environmental factors such as drought. This study monitored and analysed land use/cover changes in the Bindura district using Landsat data for 1973, 1989 and 2000 and discussed socioeconomic backgrounds for changes. A hybrid supervised/unsupervised classification approach coupled with geographical information systems (GIS) analyses was employed to generate land use/cover maps with six classes; agriculture, woodland, mixed rangeland, settlement, bare land and water. A post‐classification comparison change detection technique revealed different trends in land use/cover changes over the two periods (1973–1989 and 1989–2000). During the colonial and pre‐economic structural adjustment program (ESAP) independent period (1973–1989), the rates of agriculture and bare land changes were greater in the communal areas (CAs) than in the large‐scale commercial farms (LSCF), with ‘woodland to agriculture’ and ‘mixed rangeland to agriculture’ conversions dominating. In contrast, land use/cover changes in the LSCF increased more than the CAs during the post‐ESAP independent period (1989–2000), as ‘woodland to agriculture’, ‘mixed rangeland to agriculture’ and ‘woodland to mixed rangeland’ conversions dominated. The major land use/cover changes in the study area as derived from Landsat data are mainly due to the dynamic nature of agriculture practice such as extension of crop fields on one hand and the abandonment of croplands on the other hand, with additional factors such as wildfires and droughts. Observed trends in land use/cover changes indicate that deforestation and the encroachment of cultivation in woodland areas is a continuous trend in all the land tenure systems. Our results, therefore, suggest that an efficient and sustainable land use plan is required to reduce the rapid land use/cover changes, particularly the loss of woodland areas.

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.

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.

Monte Carlo simulations of spectral albedo for artificial snowpacks composed of spherical and nonspherical particles

The optical properties of snowpacks composed of spherical and nonspherical particles artificially prepared in a cold laboratory are investigated by measuring spectral albedos. The measured spectral albedo in the spectral region lambda=0.35-2.5 microm is compared with the theoretically calculated albedo, for which a Monte Carlo radiative transfer model is employed for multiple scattering combined with the Mie theory and the ray-tracing technique for single scattering by snow particles. Since the spherical particles are a little aggregate, the effects of a cluster of the spheres on snow albedo are examined using a generalized multiparticle Mie-solution model [Appl. Opt. 34, 4573 (1995); J. Quant. Spectrosc. Radiat. Transf. 79-80, 1121 (2003)]. The snow albedo of a cluster of the spheres can be represented with that of the singe sphere slightly larger than its component of the cluster in case of small grains. The observed albedos for the spherical snow particles agree with the theoretically calculated ones for the snow grain size measured in the snow pit work. The snow albedos for the nonspherical particles, which were dendrites, are influenced by the branch width and the branch length, based on a comparison of the theoretically calculated albedo by using circular cylindrical snow particles and the observed albedo. The snow albedo in the near-infrared region depends on the branch width only when the branch length is sufficiently greater than the branch width. The comparison between the spherical and nonspherical snow particles indicates that the spectral albedo of the nonspherical particles can be represented by using an equal volume-area ratio sphere.

Onset of rapid calving and retreat of Glaciar San Quintin, hielo patagónico norte, Southern Chile

Abstract This note records the recent rapid retreat of the terminus of Glaciar San Quintin, which drains the western edge of the Hielo Patagónico Norte (HPN) in southern Chile. In 1993, the glacier terminus was advancing strongly into vegetated ground, while from 1996 to May 2000 the glacier underwent a transition between advance and retreat. A satellite image taken in 2000 showed that the ice front was undergoing substantial retreat and calving into proglacial lakes. Our research suggests that the glacier had lost an average of 1.89 km2 a−1 in ice surface between 1996 and 2000. The total surface loss is 7.55 km2, by far the largest retreat documented for the glaciers of the HPN since 1945.

MORPHOLOGY, SURFACE CHARACTERISTICS, AND FLOW VELOCITY OF SOLER GLACIER, PATAGONIA

The morphology and surface characteristics of the Soler Glacier, Patagonia, were analyzed utilizing vertical aerial photographs taken in 1984 and 1986, coupled with a field survey. The bedrock topography was measured in a gravimetric survey. The three subglacial cross-profiles indicate that a longitudinal subglacial ridge runs roughly along the median of the glacier. The major surface features recognized include an ablation medial moraine, ice-cored lateral and supraglacial moraines, ice mounds, crevasses, supraglacial stream systems, and five sets of ogive patterns. Ogive band spacings indicate that ice flow velocities range from less than 100 m yr-1 near the snout to more than 300 m yr~1 below icefalls and bedrock cliffs. These values generally agreed well with the distance ice mounds moved and the velocity inferred by extrapolation of two short-term field measurements.