Geology topics

Lawrence J. Toimil

Publications and source records attributed to Lawrence J. Toimil.

3 recordsLinked to original sources

USGS1979

A herringbone bedform pattern of possible Taylor-Görtler type flow origin seen in sonographs

Side-scan sonar records collected in a shallow arctic lagoon (2–2.5 m depth) reveal a herringbone pattern of current-aligned linear reflectors with branching diagonals. The major longitudinal reflectors have no detectable relief (<20 cm), are spaced 5–10 m apart, and may represent current-aligned helical cell boundaries preserved in the silty fine sand of the lagoon floor. The pattern suggests a three-dimensional flow regime of the Taylor-Görtler type.

Sedimentary Geology↗

USGS1979

Fast-ice thickness and snow depth in relation to oil entrapment potential, Prudhoe Bay, Alaska

In winter, the undersurface of the sea ice on shallow arctic shelves acts upon the sea bed directly by contact and indirectly by influencing currents and turbulence. The under-ice surface would serve as a trap for pollutants such as oil and gas released from the sea bed. A knowledge of the morphology of the undersurface of the ice is a first step in understanding the sea-bed interactions and in evaluating the quantities, configuration, and dispersal patterns of sub-ice pollutants. Investigations show thicker sea-ice correlates with a thin snow cover and thin sea-ice underlies elongate snow ridges. In early May, 1978, the relationships between under-ice morphology, sea bed morphology, tidal currents, and variations in snow thickness were studied. At three sites representing three different environments--protected bay, deep, open lagoon, and narrow tidal channel--trenches were cut through the ice. The trenches were parallel and perpendicular to the sastrugi-sculptured northeast-southwest trending snow ridge pattern. Snow depth, ice thickness, and ice drafts were measured and an upward-directed side-scanning sonar was towed to examine the morphology of the under-ice surface in an area 100 m square. Snow depth and ice thickness vary about 30-40 cm and exhibit a negative correlation--thin ice coinciding with a thicker insulating snow cover. The areal snow and ice morphology patterns reinforced the correlation. Elongate ridge and trough patterns on the under-ice surface parallel the surface snow ridge patterns on wavelengths typically 10 m wide, yielding sub-ice voids of 25 to 47 x 10 3 m 3 /km 2 (600-1200 barrels per acre). Diving observations indicate a smaller set of depressions 5 cm or less in depth, oriented parallel to the ice crystal fabric, and an escape of sub-ice released air to the snow-ice interface. The results imply that there is a seasonal stability to the snow ridge pattern and that oil concentrations under the ice would be indicated by surficial snow morphology in the fast ice zone. Spreading directions would be enhanced in the elongate dimensions of the under-ice ridges and troughs, that is, upwind and downwind. In spring, gases will leak to the surface.

Alaska↗

USGS1978

Ice-gouged microrelief on the floor of the eastern Chukchi Sea, Alaska: a reconnaissance survey

Side-scan sonar and bathymetric records obtained from 1,800 km of trackline from the eastern Chukchi Sea continental shelf, between water depths of 20 and 70 m show the ubiquitous presence of furrow-like linear depressions produced by gouging of the sea bed by ice keels. These sea bed micro-features are regionally widespread but are not uniformly distributed. Furthermore, the microrelief, texture, and lithologic structure of sea bed sediments have been significantly modified by the disruptive processes associated with ice gouge formation. An analysis of some 10,.200 individual gouges shows that the density of ice gouges increases with increasing latitude, increasing slope gradients, and decreasing water depth. Across the northern half of the shelf few trackline segments are free of ice gouges; in the southern portion numerous segments contain no ice gouges. However, ice gouges extend at least as far south as Cape Prince of Wales Shoal. Densities of over 200 gouges per km of trackline are not uncommon in water depths less than 30 m ,but no values higher than 50 km are encountered in water deeper than 50 m. No ice gouges have been observed in water depths exceeding 58 m. Saturation ice gouge densities (greater than 300/Pan) occur along the eastern side 6f Barrow Sea Valley and the northeast flank of Hanna Shoal. Maximum gouge incision depths per km of trackline are greatest in water 36 to 50 m deep . A maximum incision depth of 4.5 m occurs in the 35-40 m water depth interval. Individual ice gouge events wider than 100 m, most produced by multi-keeled ice fragments, are found between 31 and 45 m depths. The dominant azimuth of gouge furrows shows no preferred orientation on the Chukchi Sea shelf; only locally does bathmetric control of the trend of gouges appear. The occurrence of current-produced bedforms within individual ice gouges suggests an interaction between slow-moving grounded or gouging ice keels and swift currents. In other cases, current-produced bedforms, interpreted as being in equilibrium with existing flow regimes, lie adjacent to ice gouges, suggesting contemporary ice gouging to water depths of at least 43 m.

Open-File Report↗