On May 18, 1980, Mount Saint Helens erupted. Scientists knew something was going to give for over a month, but an earthquake had created a landslide, which initiated a chain of events concluding in volcanic eruption. The initial avalanche revealed half-melted volcanic rock on the north side of the volcano. As this half-melted rock was exposed to high internal pressures, a devastating volcanic eruption occurred. Rock, gas, ash, and pumice all came blasting out of the zone that the landslide had uncovered, obliterating trees as far as nineteen miles away. The deadly hot gases caused snow, ice, and even entire glaciers on the mountain to melt with astonishing rapidity, creating lahars, or volcanic mudslides, which flowed all the way to the Columbia River, a full fifty miles away!
If the direct damage and destruction weren’t trouble enough, volcanic ash from the eruption fell as far away as Oklahoma, causing darkness in areas, and power blackouts. The force of the explosion itself was calculated to be seven megatons of thermal energy, and the total energy from the Mt. Saint Helens eruption and all its effects was estimated to be well over one thousand times that of the atomic bomb dropped on Hiroshima. Hence, the age-old question resurfaced — what is the source of volcanic activity? There was a time when magma was considered to be molten rock from the earth’s mantle, but the study of earthquake waves shows that the mantle is much too far down to be the source of volcanic eruptions. So where does magma come from?
What is a Volcano?
Unfortunately, nobody knows for sure how and why volcanoes occur, nor where the magma comes from. It is thought that there are spots of molten rock as close as twenty miles under the surface. Since basalt is the primary rock ejected from volcanoes, scientists have pointed out that there is enough heat twenty miles under the surface of the earth to melt basalt, but only if the pressure around the basalt is reduced. Another interesting thing to note is that most, but not all, volcanoes occur along the edges of the earth’s plates. Could there be some connection?
What Are the Different Types of Volcanoes?
Volcanoes are formed by different events, which account for several distinct shapes. Probably the most often pictured is the composite cone volcano. It is merely a mountain of hardened lava, volcanic ash, and other various volcanic debris deposited in layers, sloping away from the center of the cone from which lava issues. Mount St. Helens is considered a composite volcano (also called a stratovolcano).
Another common volcano type is the cinder cone volcano in which hardened lava fragments piled up around the vent, forming a mountain. Shield volcanoes are lava flows piled up onto each other forming a relatively short but wide volcano. The last significant type of volcano is the lava dome. A lava dome volcano is formed by vicious lava blowing out and piling up around the volcano’s vent, and then solidifying. Internal pressures cause the lava mass to crack until the whole lava dome expands. As lava continues to flow and solidify, the structure grows.
The 1980 eruption of Mt. Saint Helen was just another volcanic eruption, but on a grander scale, with its massive force flattening things as far as nineteen miles away. Though no one to date understands exactly why they erupt, volcanoes offer extensive opportunities for study of the earth’s surface and what occurs below.
Mount St. Helens Eruption
There was apparently no video. This clip has been put together from stills taken by a USGS volcanologist who lost his life in the eruption. (You may want to install an ad blocker before viewing.)
Mount St. Helens Eruption Summary
A timeline for the May 18, 1980, eruption.
Eruption of Mount St. Helens: Past, Present and Future
Description of what occurred before and after the eruption.
May 18 Devastation Map
Location and type of effects of the eruption.
Mount St. Helens Before, During and After
Photos of the event and aftermath.
Mount St. Helens
Published scientific results from the USGS in HTML booklet form includes photos and illustrations.
Mount St. Helens in Washington State
Article from Answers in Genesis.
Eruptions in the Cascade Range During the Last 4000 Years
Mount St. Helens is part of this volcanic range as explained in this download at USGS.gov.
Principal Types of Volcanoes
Cinder cone, composite, shield, and lava dome volcanoes explained.
Plate Tectonics Theory
Volcanoes on the plate boundaries explained.
Natural Hazards Viewer: Volcanoes
Notice their placement. From NOAA.
Hawaiian Volcano Observatory Webcams
Glossary of Volcano and Related Terminology
Fact Sheet: Volcanoes
FEMA download tells how to prepare for one.
Mount St. Helens VolcanoCam
Two cameras always have the volcano in view.
Anatomy of a Volcano
Interactive activity from NOVA.
Lots o’ Lava
Make your own volcano…perhaps outside….
Make a paper volcano model of Mt. Fuji.
Color volcano model of a stratovolcano at USGS.gov.
Construct and analyze.
Volcanoes by Robert I. Tilling
Public domain title from the U.S. Geological Survey — complete and in an easy-to-read format.
Unit Studies & Lesson Plans
A Teachers Guide to Stratovolcanoes of the World
Informative 64-page download at NOAA.gov about various volcanoes around the world.
Teacher packet from USGS. Six lessons with activities, printables, and poster. Very well done!
Living with a Volcano in your Backyard
Subtitled “An Educator’s Guide with Emphasis on Mount Rainier,” this 3-unit guide offers a multitude of information and activities. Makes a great research and evaluation guide. Very large download.
Uncovering Earth’s Secrets
25-day Core Knowledge lesson plan covering geology including volcanoes.
8-lesson Core Knowledge lesson plan with activities and printables.
Printables & Notebooking Pages
30 Cool Facts About Mount St. Helens
Large poster from USGS.
Printable infographic for notebook from Weather Underground.
Volcanoes Notebooking Pages
Simple notebooking pages for copywork, narrations, or wrapping up.