Saturday, November 04, 2006

Mercer Island geologic map

The University of Washington has a new map of Mercer Island's geology.  I don't see anything particularly unsettling (so-to-speak)about our neighborhood:

We're sitting on "Vashon subglacial till" (purple), which is between Vashon recessional deposits (orange) and "Pre-Fraser non-glacial deposits" (green). The jagged lines near us are "scarps", which in our case are those big dirt cliffs behind our neighbors across the street.

No fault lines, no artificial fill: just nice glacial deposits from the Pleistocene Era.


Larry said...

Richard, I'm interested in your post. I just hiked along a little visited ravine on Mercer Island, finding an abundance of smooth rocks. My guess was that the island is a glacial deposit, which you appear to confirm.

Unfortunately, your graphic is not showing, and your hotlink doesn't address MI's glacial history.

Might you have some other references I can see to understand better the island's - as well as Lake Washington's - origins?

Thanks, Larry (resident of MI since 1950)

Richard Sprague said...

Thanks for your interest, Larry.

That's an old post, so I'm not sure what happened to the graphic, but it's easy to create again: just go to the UW site and look up your neighborhood.

I wrote this after hearing about a lecture at the community center--you might find more info if you dig up on the mercer island government site, especially from late 2006 or so.