Where do the tremendous forces originate: That drive massive eruptions tens of thousands of feet in the air? That can change the sunsets world wide for years? That can cool the earths average temperature causing miniature ice ages? That can blast the tops and sides off mountains? That can produce a sound so loud it is heard 8,000 miles away? That can virtually disintegrate volcanic islands? Why: If a volcanoes source of magma/lava is from the magma pool that fills the entire inner Earth, then why don't volcanoes keep erupting indefinitely? Granted steam and gasses contribute to the eruption by generating tremendous preasure but this preasure should blow downard into the earths magma pool or if the Earths magma pools pressure in so powerful that the magma is forced to the surface then the preasure from the Earths magma pool should never subside and the eruption should go on indefinitely and constantly grow larger and larger.  In the graphic the Lithosphere beneath the ocean is drifting into the continental crust. As it begins its decent beneath the continent enormous forces push against the crust causing it to arch upward and thus forming a coastal mountain range such as the Cascades. This arching also creates a large dome beneath the coastal mountains. If conditions are right this dome fills with hot fluid magma. Then as the Lithosphere advances further it cuts the magma off from it's source and isolates it as in the picture. In the case of the subduction zone off the coasts of western Canada and the western United States the Juan De Fuca oceanic plate is being forced beneath the Cascadian plate. As the Juan De Fuca plate continualy advances it cuts off huge reserviors of magma and then squeezes them like a baker squeezing decorative icing onto a cake. As the Juan De Fuca plate continues its advance the Occluded magma is then subjected to the same extreme pressures and energies that formed and pushed up the coastal mountains. The Jan De Fuca plate pushes up beneath the magma dikes forcing the Cascade Mountains upward. This upward preasure drives the magma upward and as it advances into the base of the mountains gasses including water vapor and sulpher are desolved into the magma chamber. The isolated dike of magma has nowhere to go but up and is manifested to us as a volcano. An eruption only temporarily releives the preassure. As the Jaun De Fuca plate continues its advance the preasures rebuild. A very small advance of the Jaun De Fuca plate will increase the preassures on the isolated magma reseervoirs subatantialy. As long as the magma dike is molten the volcano lives but when the magma cools the volcano becomes extinct and dies. It may be possible that several volcanoes could share the same magma reservoir which would explain why nieghbing volcanoes became restless when Mount St. Helens erupted. The bear Tribe Indians have a saying about Mount St. Helens and Mount Rainier that says, "When sister calls big brother soon answers". If magma chambers are shared by two or more volcanoes, and intolerable pressures develop the weakest link in the volcano chain will be the one to burst. Click here to watch movie http://www.oocities.org/wwindmills/vocvid/volcano_0005.wmv
The
unprecedented record setting crustal movement near Sumatra may
reshuffle magma dike pressures in the area and I welcome comments
and Questions and look forward to hearing from you!
wwindmills@comcast.net
Bountiful High, Utah class of 58 Placed Feb, 2007 Last update Sept 4, 2008 |