Lecture #7 Volcanic Origins of the Columbia River Gorge: A Tangled Tale of Magma and Water

Although nearly a dozen large volcanic landforms dominate the Pacific Northwest skyline, there are thousands of volcanoes in the Cascades arc that have been active in the last 2.6 million years. The processes by which these volcanoes drive mountain-building in volcanic arcs, like the Cascades, define a regional volcanic history that is the basis for assessing the likelihood of future eruptions and understanding the volcanic landscape. But volcanoes operate on time and spatial scales far outside that of direct human observations, so deciphering the volcanic history is challenging. There is perhaps no better place to study these processes than in the Columbia River Gorge, a landscape profoundly shaped by both magma and water. The Columbia River is the largest river in the world to intersect a volcanic arc. Persistent erosion by the river over at least 17 million years provides a rare glimpse into a cross-section of the Cascades mountains, including a geologically recent (past several million years) pulse of high volcanic activity accompanied by uplift and faulting. What the river reveals offers insights into magmatism throughout the Cascades, mountain-building, and the role of water in shaping these vertical landscapes. Join Earth scientist Leif Karlstrom as he shares how his research group is using everything from geologic maps and drones to computer models and rappelling down waterfalls in an effort to untangle the complex history of magma and water that built our Cascade Mountains.