************************************************************* From: Thomas Pierson <tpierson@xxxxxxxx> ************************************************************* Colleagues: If you have an interest in the variety of volcaniclastic deposits that can be emplaced downstream of active volcanoes, please consider the following one-day, post-meeting field trip at the 2009 GSA Annual Meeting in Portland, Oregon: Field Trip 423: Eruption-related lahars and sedimentation response downstream of Mount Hood: Field guide to volcaniclastic deposits along the Sandy River, Oregon. We will examine a variety of debris-flow, hyperconcentrated-flow, and volcanic fluvial deposits in both proximal and distal settings, which were mobilized in response to two late Holocene dome-building eruptions at Mount Hood. Although the Cascades are in a temperate climatic setting with typically low- to moderate-intensity rainfall, syn- and post-eruption sedimentation resulted in channel aggradation up to at least 28 m in the lowermost reach of the Sandy River, over 60 km downstream of the volcano. Dendrochronologic dating of terraces suggests that aggradation during the later of the two eruptions was related to the downstream passage of a bed-material sediment wave that traveled 83 km in less than 3 decades. Vertical changes in river bed elevation here rival those from large explosive eruptions in tropical, high-rainfall-intensity climatic settings, such as Mount Pinatubo. How is this possible? Come join in the discussions and see a variety of well-exposed volcaniclastic deposits. Many thanks, Tom Pierson ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
