Krakatoa
Perhaps the best example of the massive and sudden capabilities of a volcano is Krakatoa. Like the Cascades, this volcano is formed from a suduction zone (map). The Australian (oceanic) plate is being suducted under the Eurasian (continental) plate (map). (Click on the links to view the maps of this area.)
Unlike Hawaii, Krakatoa was an uninhabited composite volcanic island in Indonesia. On August 27, 1883 Krakatoa didn’t erupt—it exploded—the entire volcano and island vaporized in a massive explosive eruption (map). (Click on the link to see how much of the island disappeared.) The sound of the explosion was heard 3,000 miles away. The ensuing tidal wave caused by the massive shockwave drowned 36,000 people. Eleven cubic miles of the island vanished and were pulverized by the eruption into fine ash and rock particles that blocked out the sun for two days to a distance of 250 miles from the volcano.
Go to the story Remembering Krakatoa's Cataclysm and click the Real Audio or Windows Media link in the top middle of the page to listen to the story.
If you need a transcript of the story, it can be purchased from NPR at the above website.
Rather than explain the awe of this eruption, I’d like you to listen to a news excerpt of this story from National Public Radio. In the interview, Geologist and writer Simon Winchester is interviewed about his recent book on the eruption. In this interview, Winchester presents details of how word of the event spread and what it was like near the scene in the days leading up to the blast, and about the short- and long-term aftermath. The final explosion created a noise said to be the loudest heard in recorded history.
Additional case study information can be found in this article from History Magazine.
Philippine Volcanoes: Pinatubo and Mayon
Located in a similar region of the world as Krakatoa are the islands of the Philippines. This island nation is built on volcanoes that formed from a complex suduction zone. The islands are essentially being squeezed and buoyed up by the subduction of two major plates: The Philippine (oceanic) plate subducting under the eastern edge of the islands, and the Eurasian (continental) plate subducting under the islands from the west. Yes, I said a subducting continental plate. This area is broken up into many “micro-plates.” Since subduction is dependent on the relative density of the converging plates, it is possible for a continental plate to subduct (as it does here). As you can imagine, this leaves us with complex lavas, a mixture of continental and oceanic crusts which, as expected, form composite volcanoes.
While the book and this Module discusses the famous eruptions of Mt. Pinatubo in 1991, this case study will focus on the current (2009 – 2010) eruption of the Mayon Volcano. Click here for a map of these two volcanoes. Because of its tectonic setting, you would be correct in deducing that the Mayon Volcano has a mixture of both basaltic and andesitic rock.
Since the Fall of 2009, the Mayon Volcano has been rumbling. On December 14, 2009, the volcano finally erupted, releasing lava and ash. (Click here for a picture and short (one page) CNN story. Click here for a 2 minute youtube video documenting the eruption. You can see the lava and ash flow; and, incidentally, a worker in a field near the volcano!) Over 50,000 people were evacuated from the area and scientists at the Philippine Institute of Volcanology and Seismology believed that a larger-scale eruption is imminent. In February and early March of 2010, this alert was lowered. However, the Mayon Volcano continues to be closely watched as it is the Philippines most active volcano. (The links in this page are not required reading/viewing.)