What a sight we are treated to this morning. As we re-enter the Columbia River Gorge on our return to the Pacific, we stop at the delightful little town of Hood River, Oregon. Mt. Hood looms above us as we board the historic train that takes us down the flanks of this most recognizable peak of the northern Cascades. Fresh snow and fall colors give us many good opportunities to photograph this 11,235 foot, nearly perfectly conical volcanic peak.
The geologic processes which gave rise to Mt. Hood and the rest of the Cascades were very different from the ones that formed the basalt rocks of the Columbia River Gorge pictured on this web site three days ago. While the basalt once issued from deep fissures fairly gently and flowed through the Gorge behaving like a fluid, the Cascades were created by many violent explosions of gas and rock. This difference in eruptive style results from differing rock chemistry which is determined by the depth from which the molten material is coming. Basalt rock comes from very deep in the earth and in this area may have issued from a crater made by a meteor impact in southeast Oregon, seventeen million years ago. The molten rock that rises to form the strato-volcanoes of the Cascades comes from a shallower depth and is created by the only plate subduction zone in the lower 48 states, which lies just off the coast of Oregon and Washington. This generator of volcanoes and earthquakes is the subject of much interest during our shipboard geology discussions.
