Abstract

Colluvium and debris-flow deposits differ from each other and from glacial till and glacial outwash deposits in Durango, CO, in terms of sedimentological properties evaluated using laboratory testing. Testing included grain-size analysis, Atterberg limits, specific gravity, visual angularity, and uncompacted void content (UVC). Grain-size analysis showed that colluvium, glacial deposits, and debris-flow deposits had different grain-size distributions (GSDs) that occupied fields on a GSD graph with some overlap. Debris-flow deposits had the most gravel-sized grains, and colluvium had the most silt- and clay-sized grains, while glacial till and glacial outwash had very similar GSDs between colluvium and debris-flow deposits. Comparisons of angularity to gravel-to-fines (G/F) ratio provided a second graphical method for discriminating between debris-flow, colluvium, and glacial deposits. Generally, colluvium and debris-flow deposits were more angular than glacial till and outwash. Additionally, several linear correlations were recognized between lithology of grains and sedimentological and geotechnical properties, the most significant of which were: (1) The angularity of gravel in glacial till and outwash was positively correlated to sandstone gravel content, (2) the plasticity index of outwash fines was positively correlated to the metamorphic gravel content, (3) the amount of outwash fines was positively correlated to sandstone and metamorphic gravel content, while it was negatively correlated to carbonate gravel content, and (4) rounded and sub-rounded gravel content in outwash was positively correlated to carbonate and extrusive igneous gravel content. This study provides insight into the geomechanical differences between depositional mechanisms in similar semiarid environments.

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