A Summary of Interacting, Surficial Geologic Processes and Potential Geologic Hazards in the Norton Basin, Northern Bering Sea
Authors: Thor D.R. , Nelson C.H. 
Published: December 2007

Future developers of the Bering Sea epicontinental shelf will have to cope with a variety of interacting or synergistic surficial geologic processes and potential hazards. These include moderate tectonism and resultant faulting, thermogenic gas seepage, seafloor gas cratering, sediment liquefaction, ice gouging, sour depression formation, storm-sand deposition, and large-scale bedform migration.

Introduction

Studies of potential geologic hazards on the Norton basin seafloor in the northern Bering Sea (Fig. 1) were conducted by the USGS to evaluate oil and gas lease tracts for Outer Continental Shelf (OCS) leasing. The data base for this evaluation included 9000 km of high-resolution geophysical tracklines (Fig. 2), 1,000 grab samples, 400 box cores, and 60 vibracores. In addition, hundreds of camera, hydrographic, and current meter stations have been occupied during the past decade by USGS, National Oceanic and Atmospheric Admin. (NOAA), and U. of Washington oceanographic vessels. The northern Bering Sea is a broad, shallow epicontinental shelf region covering 200 000 km of subarctic seafloor between northern Alaska and the U.S.S.R. (Fig. 3). The shelf can be divided into four general morphologic areas:the western part - an area of undulating, hummocky relief with glacial gravel and transgressive-marine sand substrate;the southeastern part - a relatively flat, featureless plain with fine-grained, transgressive-marine sand plain with fine-grained, transgressive-marine sand substrate;the northeastern part - a complex system of sand ridges and shoals with fine - to medium-grained sand substrates; andthe eastern part - a broad, flat marine reentrant (Norton Sound) part - a broad, flat marine reentrant (Norton Sound) with Holocene silt and intercalated very fine-grained storm-sand substrate underlain by gas-rich, peaty Pleistocene mud.

A detailed discussion of Pleistocene mud. A detailed discussion of bathymetry and geomorphology of the northern Bering Sea is given by Hopkins et al. The northern Bering Sea is affected by a number of dynamic factors: winter sea ice, high winds, storm waves, and strong currents (geostrophic, tidal, and storm). The sea is covered by pack ice from November through May. A narrow zone of shorefast ice (sea ice attached to the shore) develops around the margin of the sea during winter months; around the front of the Yukon River delta, shorefast ice extends 50 km offshore. During the open-water season, the sea is subject to occasional strong northerly winds. In the fall, strong south-southwesterly winds cause high waves and storm surges along the entire west Alaskan coast. Throughout the year a continual northward flow of water is present with currents intensifying on the east side of strait areas. Although diurnal tides are very minor (less than 0.5 m), intense tidal currents are found in shoreline areas and within central Norton Sound. Potential geologic hazards discussed in our report include faulting, thermogenic gas seepage, biogenic gas-charged sediment and cratering, sediment liquefaction, ice gouging, current scouring, storm-sand migration, and mobile bedform dynamics. These geologic hazards may pose problems for the future development of Norton basin resources.