Hercules Dome - An Overview From the US-ITASE Deep Radar

Hercules Dome (86° S, 105° W) is an elongated, approximately 100 m local rise in the ice surface topography between the Horlick and Thiel Mts. about 400 Km from S. Pole and 100 Km up-flow from "The Bottleneck" linking the East and West Antarctic Ice Sheets. It was first identified by the USGS from USN aerial photographs taken in 1959-60 and further delineated by the SPRI-NSF-TUD airborne aerial radio echo sounding program in 1967-79. The Ice Core Working Group identified Hercules Dome in reports dating from the late 1980's as a possible site for a deep ice core because of its location at the boundary between the East and West Antarctic Ice Sheets where it may have the possibility of showing changes in the WAIS over the last 200,000 years. Recent interest has been rekindled because of the US-ITASE traverse which has provided the first ground-based observations of the area. We completed 120 km of radar profiling in an elongated grid pattern approximately 5 by 50 Km and roughly perpendicular to the main ITASE traverse route from Byrd to South Pole. Bed topography and internal stratigraphy down to 70% of the ice thickness is well-depicted in these surveys and we have picked the bed and a number of prominent, continuous internal layers from these profiles. These data reveal that Hercules Dome is approximately centered over a bedrock low, possibly a basin, some 30-50 Km in extent. The greatest ice thickness under the dome area is 2800 meters with bedrock elevations 200 meters below sea level. Within 15 to 25 Km in each of the directions surveyed, the bed rises 900 to 1400 meters from the low under the dome. Internal stratigraphy is well-behaved throughout the dome region in contrast to nearby areas along the traverse route which show marked disruptions of internal layers (Welch et al., this session). Although model studies will be required to explore details more fully, it appears that ice flow in the vicinity of the dome has not undergone major changes throughout at least the period of time represented by the upper 2000 meters of ice thickness. Other US-ITASE experiments should soon be providing additional glaciological information on Hercules Dome including modern accumulation rates, shallow radar, ice core chemistry and surface velocity.