The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . easternberings00hood Year: 1981 Sedimentary processes and potential geologic hazards 257 Figure 15-7. Distribution and density of biogenic gas-generated craters on sea floor of Norton Sound, sliowing isopachs of Holocene mud derived from the Yukon River and deposited since Holocene postglacial sea-level rise (from Thor and Nelson 1979). m thick of impermeable Holocene mud. We postulate that the gas escapes during periodic storms, forming craters at the surface. The storm processes init
The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . easternberings00hood Year: 1981 Sedimentary processes and potential geologic hazards 257 Figure 15-7. Distribution and density of biogenic gas-generated craters on sea floor of Norton Sound, sliowing isopachs of Holocene mud derived from the Yukon River and deposited since Holocene postglacial sea-level rise (from Thor and Nelson 1979). m thick of impermeable Holocene mud. We postulate that the gas escapes during periodic storms, forming craters at the surface. The storm processes initiate rapid changes in pore-water pressures because of sea-level setup, seiches, erosional unloading of cover- ing mud, and possible sediment liquefaction from cyclic wave loading (Clukey et al. 1980). Gas venting and sediment craters or depressions which seem to form during peak storm periods may be a potential hazard to offshore facilities because of the rapid lateral changes in bearing strengths and collapse of sediment which form the craters. Sediment collapse may also expose pipelines to ice-gouging hazards. During nonstorm conditions, the upper several meters of sediment at many locations has reduced shear strength because of the near-surface gas satura- tion and presence of peat layers. Choosing locations for structures will require extensive testing of the substrate to determine the extent and activity of gas cratering at a given site. Liquefaction The assessment and prediction of sea-floor stability are affected by the possibility that a sedimentary deposit will liquefy under cyclic loading and behave as a viscous fluid. The liquefaction potential of Norton Sound sediment is great in central Norton Sound and in the vicinity of the western Yukon prodelta (Clukey et al. 1980, Olsen et al. 1979). Possible causes of liquefaction include upward migration of gas from thermogenic and biogenic sources, earthquakes, and ocean waves. Bottom features that may be caused in part by
Size: 1720px × 1163px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
