Till beneath ice stream B: 2. Structure and continuity

During the 1984–1985 Antarctic field season, 8.3 km of high‐resolution seismic reflection data were collected in order to image a thin till layer beneath ice stream B, West Antarctica. Two parallel seismic reflection lines were oriented transverse to ice flow. These data show that the till layer varies in thickness but is continuous over almost the entire length of the profiles with an average thickness of 6.5 m. The upper surface of the till layer is smooth, but the lower boundary is fluted parallel to flow. These till‐filled flutes are as much as 13 m deep and 1000 m across. Nowhere on the profiles can any feature be discerned to penetrate more than a few meters into the ice from the bed. Reflection events from lithified sediments of unknown type are observed to be truncated by the till in an angular unconformity.