In addition to the case studies in your book, I want to outline two other important volcanoes and areas of volcanic activity: Mt. Rainer near Seattle, Washington; and Krakatoa in Indonesia. With the recent activty at Mt. St. Helens in 2004, additional information is posted on Mt. St. Helens--building on the information already listed in your textbook.
Mt. Rainier
The 13 potentially active volcanoes of the Cascades Ranges of Washington,
Oregon, and California. Eleven of the volcanoes have erupted in the past
4000 years (Earth Pearson/Prentice Hall). Seattle-Tacoma Washington is perhaps the U.S. city at greatest risk to a volcanic eruption. Even though the state of Hawaii is a volcano, the Hawaiian eruptions are gentle and predictable. This is not the case for Mt. Rainer, the composite volcano that looms within 30 miles of the Seattle-Tacoma metropolitan area in Washington State. Mt. Rainer has erupted several times in human history, including as recently as a few hundred years ago. This composite volcano is created from a subduction zone (map): the Juan de Fuco (oceanic) plate is subducting under the North American (continental plate). (The links in this paragraph are not required reading.)
As we learned earlier in the discussion on pyroclastic debris and mud flows, it’s not the lava that places Seattle-Tacoma at risk; it is the possibility of mud flows and ash flows that can travel great distances at high speeds. As the risk map to the left shows, a moderate eruption could send a lahar (mud flow) into the Tacoma suburbs and Puget Sound. The lava flows and debris flows would only affect the remote areas far away from populated areas. (If you didn’t see it the last time, click here to watch this short video on the potential of these lahars to cause damage to this area.) If you would like to read more, visit this USGS site.
Map of Mt. Rainier and vicinity showing potential hazards from lahars
(debris flows), lava flows, and pyroclastic flows (Keller; Pearson/Prentice Hall).Because Mt. Rainer is a composite volcano, it can erupt suddenly and violently with little warning. People would not be able to evacuate in time to avoid the lahars. However, if some warning existed, as was the case in Mt. St. Helens, an evacuation could easily take place. If no warning exists, the Seattle-Tacoma region could be subjected to a sudden inundation of ash and mud that could easily result in a high number of casualties. In 2004, Pierce County (and the City of Tacomoa) used results from a USGS pilot study (started in 1999) to create a lahar detection system to aid in providing advance warning of these debris and mudflows. In 2008, the USGS finally developed a “Pilot” lahar warning program in King County (Seattle). (The links in this paragraph are not required reading; although, the second link does list some important “Response Steps” just in case you wanted to know what to do if you hear the lahar sirens going off if you should ever be in the Seattle-Tacoma area.)