Reports
&
Analyses

Possible interpretations of linear features

This page discusses features that may have been generated by faulting near Lake Iliamna, and provides greater depth to what is presented on our possible Lake Clark Fault page.

Beyond the main interpretations we considered for the two linear features we examined, there are a number of alternate explanations that are less likely. All possible explanations that we considered, reasonable or unreasonable, are presented briefly in this table.

Possible origin	Braid-scarp	Slope-disruption
Fault trace	Good agreement: If a zone of unbedded sediment underlying the scarp records disruption, this is a trace of a fault that ruptured after the fluvial sediment was deposited (likely the late Pleistocene).	Good agreement: This feature appears to offset a number of diffuse gullies in the hillslope. This offset of 120 meters would be plausible if this surface was unglaciated at the last glacial maximum, which is consistent with thick (1 m) of loess accumulation on the surface.
Fluvial scarp	Possible agreement: A zone of indistinct bedding in fluvial sediment underlying the scarp could possibly be the buried remains of an active fluvial scarp. However, the zone of indistinct bedding dips down towards the upper part of the scarp, and extends deeper than the lower end of the scarp, which makes the feature difficult to interpret as a fluvial scarp.	No Agreement: A fluvial scarp would be a nearly planar, gently sloping shelf along the valley wall. This feature varies in slope along its length, crosses several minor divides, and is too steeply sloping in some places.
Lateral moraine	No agreement: The feature crosses a sedimentary surface covered by braided fluvial scars, so it is younger than the most recent glaciation.	Possible agreement: This feature might be the trace of the edge of a glacier flowing down toward Upper Talarik Creek. However, the glacier whose edge created the moraine would have to be thin and steep, which seems unlikely in the broad open valley below. Also, the feature does not appear to curve around the hill it descends, as a glacier would be expected to.
Linear bedrock weakness	No agreement: The feature occurs on a depositional fluvial plain that would conceal any possible bedrock weaknesses. The sediment is likely many meters thick since it is bounded on several sides by kettle depressions.	Very little agreement: Raised areas adjacent to the feature are soft sediment, as evidenced by rotational slumps on a low angle (<10%) slope. Local high-points are rounded and diffused sediment with isolated boulders, likely also soft-sediment.
Gully	No agreement: The feature is a step on a nearly flat surface, and thus nothing like a gully.	No agreement: The feature crosses several minor divides, and so does not drain in the same direction along its length.
Basal striation from glaciation	No agreement: The feature crosses a sedimentary surface covered by braided fluvial scars, so it is younger than the most recent glaciation.	Very little agreement: Though the feature has a trend that could be aligned with glacial flow, there are no similar features in the area, and basal striations 10 km away are more uniform in width, have a greater width to length ratio, and are oriented about 40 degrees differently.