Case Study 4. The Cascades – Connecting Canada and the United States
Geophysical aspects and history of activity The Cascades form part of the Pacific Rim volcanic zone and result from the Pacific Plate and its smaller companion the Juan de Fuca Plate being subducted under the North American Plate (Hill, 2004, pp4-7). This 960km long area lies between 96 and 240km offshore, but produces its tectonic effects in the Cascade range. These effects are eruptions and earthquakes, all of which are extreme events. Most of the major peaks are stratovolcanoes made up of layers of lava and other volcanic debris, and many are quite young (e.g. Mt St Helens), although some such as Mt Rainier are thought to be considerably older. However, almost all the major volcanoes shown in Figure CS4.1 have erupted in the past 4000 years, with 7 being active within the past 250 years (Dzurisin et al, 2008). All are presently classed as active and can be expected to erupt in the future.