Unusual Feature of Mount St. Helens Explained

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By using advanced image analysis and close observation of the Earth’s crust, scientists how found out why Mount St. Helens is located outside of the Cascade Arc volcano group.

The Spirit Lake batholith, a giant rock formation ranging for almost 30 miles in diameter, seems to have deviated magma and molten rock to the west zone of the arc, leading to the formation of the most active volcano in the region just outside of the arc zone. The results, part of a joint study done by the National Science Foundation and the U.S. Geological Survey, will be soon published in a peer-reviewed journal.

Previous studies were made using seismic analysis. By observing both natural earthquakes, and artificial ones created by well-placed explosive chargers, researchers can study the properties of subsurface rock form their different reaction to sound waves. Information about temperature, density and structure can be obtained in this manner.

A more modern method is the use of magnetotelluric or MT, which measures the conductivity of Earth’s subsurface layer. All the methods listed before are efficient on their own, but combining them will form a detailed picture of what we can find underground.

In order for the measurement s to be better, you must gather data for a longer period of time in order to maintain accuracy.  In order to explain how St. Helen researchers started with tectonics.  Large crustal blocks with marine sediments were pushed into the continent. These rocks are more permeable, allowing magma to burn its way through it. In this manner, the big batholith can be perceived as a natural plug that diverted magma which should have erupted along where the other major Cascade volcanoes are placed. The magma erupted to the west of the Cascadia Arc, resulting in the mountain we know today.

The last major eruption of Mount St. Helen ok place in the 1980. It went through a dome-building stage in the last decade and has remained dormant since. The discoveries could allow us to observe changes that take place inside volcanoes before visible signs appear.

As our second lead editor, Anna C. Mackinno provides guidance on the stories Great Lakes Ledger reporters cover. She has been instrumental in making sure the content on the site is clear and accurate for our readers. If you see a particularly clever title, you can likely thank Anna. Anna received a BA and and MA from Fordham University.