Thursday, February 6, 2014

Slogging Through Beach Sand

I found my pace slowed by remarkable sand compaction on a shore near Langley on Whidbey Island. With each step my foot would sink a good two to three inches or more into the beach. 
Deep foot prints on the beach

Being slowed by sand is to be expected when the sand is loose and dry. But in this case the moisture content and grain size distribution was such that significant compaction was taking place by simply stepping on the beach. The beach sand all along this reach of shore was the same and made for a rather awkward gait. I generally drift to the beach material with the easiest walking, but this sand was nearly uniformly distributed across the beach and wet areas meant sinking into water.

The geology along this shore reach was rather uniform as well. Shoreline bluffs of advance outwash sands deposited as the Puget ice lobe advanced into the area and then overrode the sand with some silt. The unit above the advance outwash was a recessional glacial outwash with an almost identical grain size, at least on a casual visual basis. There was no intervening glacial till, but the recessional outwash sand having not been overridden by ice were looser. 

Advance outwash sands and silty sand, Whidbey Island

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