Debris flows: a looming hazard for the Northwest

Debris flows, slurries of mud, gravel and rock, are a product of mountain erosion associated with glaciers. They are especially prevalent on volcanoes around the "Ring of Fire" that circles the Pacific that each hold great loads of volcanic debris high on their glacier-clad slopes.

Present-day debris flow dangers at Mt. Rainier were recently featured in a front page article by Sandi Doughton in the Seattle Times, based on an interview with Paul Kennard, a Park Service geologist. Here's a photo of the rocky mess at Rainier's Tahoma Creek, from The Times:

In the North Cascades, Mt. Baker and Glacier Peak are potential sources of damaging flows, and glacial retreat throughout the Cascades has laid bare huge quantities of glacial grindings so that accelerated transport to rivers must be expected.

The upcoming issue of The Wild Cascades will include more on this topic... Join N3C now to get your copy delivered to your home: http://www.northcascades.org/signup.html

Look, down at your feet - it's... geology!

From pegmatite to transform faults to strike and dip, geology can seem like another language. But what you're looking at when you look down, and when you gaze up at spectacular North Cascades scenery, is what geology concerns itself with, of course. So even if the terminology's a bit daunting, it is interesting to see a map where the boundaries aren't the arbitrary lines of politics, but instead define what's exposed at the surface.

We have the pleasure to announce a new masterpiece of geologic maps of our favorite place has been released, by none other than our longtime associate Rowland Tabor of USGS. Here's a thumbnail of his latest geologic map of the North Cascades. You can download the full version from USGS (but allow some time, it's 35MB).


Haugerud, Ralph A., and Tabor, Rowland W., 2009, Geologic map of the North Cascade Range, Washington: U.S. Geological Survey Scientific Investigations Map 2940

The USGS website Rowland created around this map features an interactive version with photos that identify the various rock types at vista points you may be familiar with. It's like an anatomy lesson on this patch of hallowed ground. Here's just one spectacular example:

One particularly "cool" map shows how far the ice sheets got during the maximum advance of the last ice age! Here's a thumbnail. CLICK HERE for a full-sized image, and just imagine! The take-away is that the extreme beauty of the peaks of the North Cascades is due in large part to massive glacial action, deepening valleys and sharpening peaks (like the "horn" in the picture above). Glaciers gave the "Pickets" their points!

And don't miss Rowland's classic hiking guide to the North Cascades for those with an interest in geology, now online! Routes and Rocks in the Mt. Challenger Quadrangle You'll find a link to it on the American Alps website's "Field Guide" page.