Washington

More On That Oso Landslide

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From The Landslide blog:

In reviewing seismic data with two distinct events, it’s not clear if a top portion slipped first, causing the bottom to give, or vice versa:

Our author:

‘To my untrained eye the initial seismic event shows a slow increase in energy release rather than an abrupt peak.  Note also that the second event appears to be much smaller than the first.  Thus, in this interpretation, the initial failure was, I think, a small, slow failure in the lower slope that destabilised the upper block of the Oso landslide, which slid onto the mass below.’

From King5 news, names, photos and a brief remembrance of those who lost their lives. R.I.P.

From The Atlantic: ‘At Least 14 Dead In Washington Mudslide’

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Photos here.

This happened about 55 miles or so north-northeast of Seattle in the town of Oso.  So far, 176 people are missing, but the death toll will hopefully not be anywhere near as high as that dreadful number. Apparently, the hill in question is made-up of glacial sandy soil and lacks a rocky, sedimentary base. It has been saturated by the recent heavy rains and undercut by a meander in the high water of the Stillaguamish river.  Many homes and properties were located in the valley below and opposite that hill.

It still isn’t safe.

From MyNorthwest.com, which has great coverage:

Geologist: Mudslide still moving, even bigger than first thought:

‘Dave Norman, Washington state geologist with the Department of Natural Resources, says preliminary assessments have determined the slide is 1500 feet long, 4,400 feet wide and over 600 feet high, with a debris field 30-40 feet deep.’

Some more photos here.

The Landslide Blog has coverage.

A lot of the soil in the region is formed from glacial deposits, and there hasn’t been much snow this winter, but for at least the last month there’s been a lot of heavy rain, and the ground has become saturated in many places.  The difference between high water between winter and summer can be striking.

Thoughts and prayers to the victims, their families, loved-ones, workers and responders.