Submarine flow tills at Victoria, British Columbia: Reply

Abstract

during winter to maintain the same average position over a year. Perhaps these cones originated by slumps on the foreslope of subaquatic outwash fans similar to those postulated by Aario (1972) and Rust and Romanelli (1975) for a glacimarine setting. The small proportion of traction current deposits may be due to subglacial streams not having a sufficiently high sediment concentration to maintain an underflow away from the efflux. Occasionally the streams were sufficiently dense to deposit outwash sand and gravel in the foreslope area. The gravity flows may have incorporated the stream gravel, sand, and mud as well as melt-out debris from englacial and basal debris layers. Mixing of these sources during liquefaction perhaps induced by iceberg calving (Powell 1980; p. 70) may produce poorly sorted sediment flows. Thick accumulation by supraglacial melt out from debris layers in a tidewater glacier may best occur where the glacier has almost retreated from the sea and ablation occurs primarily by surface melting rather than iceberg calving (the situation in facies association 111 of Powell 1981). A similar situation of ice in shallow water under mid-latitude temperature conditions was envisaged by Evenson et al. (1977) to explain stratified Quaternary tills, although their interpretation has been questioned (Gibbard 1980). Here the glacial regime and processes are similar to those of the terrestrial environment. Mudflows and debris flows may occur from the ice surface and retain their integrity whilst flowing down a shallower (though still relatively steep) slope into shallow water. If such deposits are not modified by wave action and remain preserved, then they may indicate proximity to sea level in a similar way to deltaic plains.