The Volcano Threat

by Jerry K.

This month we are going to talk about the threat posed by volcanoes here.  “But surely we have no threats, St. Helens is too far to the north and Mt.Hood is extinct.”  Wrong, Mt.Hood is not extinct but is merely dormant, like all of the major volcanoes on the PacificCoast (e.g. Mt.Ranier).  Just like St. Helens was until March 27, 1980 when she awoke.  I want to thank the folks at Volcano World for the following two paragraphs:

Mount St. Helens is a stratovolcano. When Mount St. Helens erupted on 18 May 1980, the top 1,300 ft. disappeared within minutes. The blast area covered an area of more than 150 sq. miles and sent thousands of tons of ash into the upper atmosphere.  A small, short-lived explosive event at Mount St. Helens volcano began at approximately 5:25 p.m. PST, March 8, 2005. Airplane pilot reports indicate that the resulting steam-and-ash plume reached an altitude of about 36,000 feet above sea level within a few minutes and drifted downwind to the northeast. The volcano’s rim stands at 8,325 feet.

Mount Hood (45.4N, 121.7W) is the tallest mountain in Oregon (11,237 feet, 3,426 m) and popular with skiers, hikers, and climbers. It is 45 miles (75 km) east-southeast of Portland, Oregon. Mount Hood is a stratovolcano made of lava flows, domes, and volcaniclastic deposits. Most of the volcano is andesite composition. The main cone of Mount Hood formed about 500,000 years ago. In the last 15,000 years the volcano has had four eruptive periods. During the most recent eruptive period, 250-180 years ago, lava domes collapsed and produced numerous pyroclastic flows and lahars which buried the southwest flank of the mountain. Crater Rock, a prominent rocky pinnacle just below the summit, is the most recent lava dome. Similar eruptions in the future pose the greatest risk to communities on the flank of the volcano.

The folks at Volcano World simply say that the communities on the flank of the volcano, Government Camp, ZigZag, Camp Baldwin (BSA), etc. are in the greatest risk.  This is not to say that we are not in risk.  Remember that Mt.St. Helens affected an area over 150 square miles in size.  We don’t know the size of an explosion and if Portland would feel the blast effect directly.  But ash and debris would flow down rivers such as the Sandy affecting communities downstream.  Sandy, Troutdale and the Columbia River itself could be affected.  The brunt of the airborne ash would fall on Eastern Oregon and SE Washington before settling on Boise, Idaho.

A point to remember with Mount St. Helens is that the time from when the volcano awoke in 1980 to when she erupted was just under 2 months.  None of these things takes place overnight.  Should Mt.Hood become more active (the mountain has small quakes all the time, just like Mt.St. Helens) the news would be all over the event.  We would have warnings and likely would get the notice to evacuate the city in time.  The operative word here is “likely.”  Include plans for evacuation in your 72 hour kit.  Plans that cover a local disaster (such as a house fire) and area wide disasters (such as earthquakes and volcanic eruptions).

2005 Noah’s Ark Newsletter/LDS Intelligent Living

Photo source: public domain
Department of Natural Resources, State of Washington

Ash-darkened east slopes as they appeared on March 30. This ash was derived entirely from rock pulverized by the explosively-expanding, high-temperature steam and other gases. No new rock material was produced during this stage of the eruption. Note that the location of the ash fall indicates the direction of the prevailing wind. Mount Rainier, another volcanic peak, is visible in the background.


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