Evan Lieberman Week 4 Volcanoes

Photo Credit: https://www.deloreantimemachine.com/

For my volcano field trip today, I chose to explore one of the most extreme volcanic events to occur in the continental United States, the site of Mt. St.Helens.  To begin, I jumped in my handy time machine, and went back to 1980 to observe the volcano in it's pre-eruptive state.  (And yes I'm aware that the film my time machine is based on called Back to the Future, actually now takes place in the past).

As I set the dials for my flux capacitor to 1980, I emerged from the time travel tunnels in Skamania County Washington.  

Pre-eruption Photo Credit: Pinterest

Pictured to the left is an image of Mt.St.Helens prior to it's eruption.  What we see here is is a prime example of a composite volcano or stratovolcano.  A composite(stratovolcano) volcano is defined by it's external appearance, they tend to elevate high above sea level, and have a viscous composition internally.  As a result of the viscosity of their inner composition, their eruptions tend to be thick, viscous, and travel relatively short distances.  Unfortunately, due to this same composition, these volcanoes can also have violent pyroclastic eruptions, due to the thickness trapping gasses and violently propelling pyrolclastic ash, rocks, or bombs hundreds or thousands of feet from the eruption site.  The volcanic activity associated with this particular volcano is mainly due to subduction occuring where the Juan De Fuca plate subducts beneath the North American Plate.

Digital Elevation Map of Mount St. Helens  pre-1980 topography and deposits from 1980 - 2008[Credit USGS]

I decided to spend some time in the 1980s drinking TAB, and purchasing stock in Apple, and then returned to the site (safely distant) on May 18, 1980.  What occurred at this site was an example of an explosive volcanic eruption.  In the wake of the eruption, the USGS has analyzed the contents of the eruptive material and concludes:"substantial amounts of basalt and andesite began to erupt as lava flows between phases of dacite eruptive activity. These lava flows buried large parts of a central cluster of dacite domes and flanking fans, which started the cone building in earnest [USGS]".  Essentially, the viscous basaltic and andesitic lava flows sealed all the volcanic vents, pressurizing the contents in the magma chamber.  This caused extreme pressure to build literally blowing the top off of the volcano and sending ash and other pyroclastic materials for thousands of km.  To compare here is an image of the volcano post-eruption (taken from my camera on May 19, 1980...but really from the USGS).

Photo Credit USGS

In the post eruptive state, nearly 1300 feet of the mountain's top portion was entirely removed, and ejected thousands of kms.  The sheer force of the explosion also leveled trees, property, and pretty much anything in it's path.  

In the wake of the destruction of this event, the next question on most people's minds would be, can this happen again?  The answer to that questions is two-fold, will the volcano erupt again?  Yes, I set the dial to my time machine to January 16, 2008 and observed another eruption.  This one was not explosive, but a minor eruption.  Scientists have ceased close activity to the dome, as pressure and dome formation continues into today.  It is likely, we will see another eruption of Mt.St.Helens as it is  located in subduction zone.  It is unlikely that in our lifetimes we will see another explosive eruption on the scale of the 1980 event, as the formation and building of pressure took thousands of years.  But it would be expected that an eruption on a smaller scale may well occur in the near future.  Unfortunately I have been unable to secure enough fuel in my time machine to investigate into the future.  

After my time-hopping was concluded, I returned my time machine to March 31st 2020, and resumed appropriate social distancing.