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Home Archived Aug 4, 2016

USGS Geology in the Parks

field trip map 3

FIELD TRIP STOP 13 - Artist Point; Mount Baker Highway (State Route 542)

Artist Point

Old volcanoes

At Artist Point the geologic views are even better than from the Mount Baker ski area below. The dark prow of Table Mountain dominates the scene to the west. The parking area is on the same dark andesite as Table Mountain, but to really appreciate this old lava ridge-cap, take the trail around it by way of the Galena Chain Lakes or climb over it. The top is table-like because it reflects the original surface of the thick lava flow. The Table Mountain flow in particular is so thick that geologists think it must have flowed into a constraining canyon. in which the molten rock formed a lava lake. Because of the wild, crazy columnar joints that occur along the sides of Table Mountain, volcanologist Wes Hildreth suggests the flow may have been constrained by glacial ice! Other flows of about the same age underlie the ski area and make up parts of Ptarmigan Ridge, stretching off to the southwest. After these valley-filling lava flows solidified, streams and/or glaciers worked on the edges of the flows more efficiently than in the center and eventually left the remnants as ridge tops. Erosion produced this marvelous topographic inversion after the lavas erupted about 300,000 years ago. These are not Mount Baker lavas; they erupted from an older volcanic vent located somewhere near the northeast flank of the present Mount Baker cone.

Kulshan Caldera
Kulshan Caldera filled with rhyolite ash. (a cross sectional view from the southeast; after Hildreth, 1996).

Under the dark lavas of Table Mountain, and forming white cliffs above Swift Creek, are the older volcanic deposits of Kulshan Caldera. The edge of this large volcanic depression is more or less directly beneath the parking area. The caldera is, about 2.5 miles across. It formed and was filled with volcanic tuff (the rock formed from volcanic ash) about 1.1 million years ago, when the magma chamber beneath it erupted, and its roof collapsed. Similar volcanic calderas, such as the one filled by Crater Lake in Oregon, have produced huge volumes of ash in cataclysmic eruptions. Volcanologists have identified ash deposits from the Kulshan volcanic eruption as far away as southern Puget Sound. The caldera itself is filled with over 3,000 feet of rhyolite tuff from such an eruption.

Kulshan Caldera from east
View west from Lake Ann trail across Swift Creek to Kulshan Caldera and overlying younger volcanic rocks. Crosses indicate location of the Lake Ann stock.
On to Lake Ann

Material in this site has been adapted from a book, Geology of the North Cascades: A Mountain Mosaic by R. Tabor and R. Haugerud, of the USGS, with drawings by Anne Crowder. It is published by The Mountaineers, Seattle.

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