The schoolroom view of volcanoes depicted entire cities inundated by white-hot lava, then buried under tons of ash, in times long ago and far away: Pompeii, the island of Crete, and the lost city of Atlantis, all were destroyed in the mists of antiquity. Many people believe volcanic activity in recent times has been confined to the Hawaiian Islands, where physical evidence of volcanism serves as a tourist attraction. This is only part of the picture.
Volcanic activity is current the world over, a tenuous balance between the Earth’s subterranean pressures and gravity, which provides and holds this planet’s atmosphere.
Volcanoes are a clear danger in the continental United States. Casualties of the Mount St. Helens 1980 eruption numbered 62 dead or missing. A U.S. Geological Survey scientist, David A. Johnston, was measuring activity nearly 6 miles away when the explosion occurred. Neither his remains nor his vehicle was ever found. Lawsuits filed by family members of other victims have stated the public should have been better protected.
The U.S. Geological Survey’s program for assessing volcanic hazards in that area is now housed in the David A. Johnston Cascades Volcano Observatory in Vancouver, Washington.
History
Long ago, the Earth was uninhabitable. Volcanoes raged, meteorites pounded the Earth, and comets flew en masse through the heavens. Molten lava flowed like rivers and hot ashes filled the air. Earthquakes were common. The world shook, spewed, cooled and formed a crust.
More than 80 percent of the Earth’s surface, above and below the seas, was formed by volcanic activity. Over a period of hundreds of millions of years, gaseous emissions from volcanoes formed the earliest oceans and atmosphere, which in turn supplied ingredients vital to evolve and sustain life.
Volcanic eruptions produced mountains, plateaus, and plains, leaving their signatures on the face of the Earth. These structures subsequently weathered into the geography of the present day, providing fertile soil for crops.
People gathered near volcanoes, thinking their sleeping slopes to be safe. This was not necessarily the case. A dormant volcano rekindled by subterranean forces can be incredibly destructive.
During the Vesuvius eruption of August 24, in the year 79 A.D., two cities were buried so thoroughly by hot volcanic ash and dust that they remained uncovered for nearly 1.700 years!
This catastrophe overwhelmed unsuspecting inhabitants in only a few hours. In the eruption of Mount St. Helens, property damage was estimated at $1.2 billion, as explosions of hot material and mudflows devastated 550 square kilometers of forest.
Some volcanoes are more explosive than others, depending upon the mixture of gases or steam present.
Probably the worst explosion of recent times virtually destroyed the island of Krakatoa, between Sumatra and Java, August 27, 1883. A tremendous blast heard for thousands of miles sent 21 cubic kilometers (5 cubic miles) of matter into the air. Ash fell over 300,000 square miles and shadowed the surrounding area for 21/2 days. Resulting dust in the atmosphere circled the Earth for years.
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The explosive magnitude of Krakatoa was 26 times the force of the largest 11-bomb ever detonated.
Both volcanoes and earthquakes may create tidal waves (tsunami). The Krakatoa explosion set off a tsunami that reached heights of 120 feet in various harbors, drowning 163 villages and killing 40.000 people.
This explosion was surpassed in ancient times when the flourishing Minoan civilization on Crete was destroyed in 1470 B.C. by an eruption 5 times as violent as the Krakatoa explosion, accompanied by a tsunami reaching the height of 165 feet.
Persons living in coastal areas are particularly vulnerable to tidal waves ac a concomitant of volcanic or earthquake activity.
Formation of volcanoes
Volcanoes form when magma—molten gas-charged rock—works its way up from the Earth’s mantle, located 3 miles under the oceans and 25 miles under the Earth’s crust. White-hot mantle rock is about 1.800 miles thick, but is under high pressure and therefore solid.
When additional physical or chemical processes melt the rock in the upper part of the mantle, the resulting magma finds its way upward through openings or vents to form volcanoes. The term volcano also refers to the opening or vent through which the molten rock and gases are expelled.
Gases previously dissolved in the molten rock are released as the magma nears the surface, much like champagne when the cork is removed. These gases are mainly water, along with carbon monoxide, carbon dioxide, sulfur dioxide, hydrogen sulfide, and hydrogen.
If there is a great amount of gases present, the molten rock may explode violently into the air. If little gas is present, the magma, now called lava, may pour from the vent in non-explosive flows. If the eruption is explosive, large fragments may contribute to the size of the volcano as they accumulate around the vent, as may fragments that move downslope as ash flows down the slope.
Ash particles may be carried for many miles. Very fine particles may be transported around the world. Ascending magma contains oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese. When it cools, it becomes igneous fire-formed rock.
Lava is red hot (measured at 2.200 degrees F) when it pours or blasts out of a vent. Its consistency may be that of hot tar, thick honey, or pasty, blocky masses prior to cooling when it changes to dark red, gray, black, or some other color. The contents of lava vary from site to site, depending upon the underlying composition of the Earth.
Volcanoes types
There are four main types of volcanoes: cinder cones, composite volcanoes, shield volcanoes, and lava domes.
Cinder Cones
Cinder cones are the simplest, comprising particles and blobs of congealed lava ejected from a single vent. They rarely tower 1,000 feet over their surroundings. These bowl-shaped craters are numerous in western North America. The order of events is eruption, formation of cone and crater, then lava flow.
Composite
Composite volcanoes are sometimes called stratovolcanoes and may rise to a majestic 8,000 feet above their bases. They are characteristically steep-skied and built up of symmetrical lava flows, volcanic ash, cinders and blocks. Examples are Japan’s Mount Fuji, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens and Mount Rainier in Washington.
The crater at the summit contains a central vent or a clustered group of vents. Lava flows either through breaks in the crater wall or from fissures on the flanks of the cone, building up the cone.
When the volcano becomes dormant, erosion begins to eat away at the cone to form a volcanic “plug.” Crater Lake in Oregon is a depression, or caldera, formed when the top of this composite volcano collapsed from repeated explosions and lava drain.
Shield
Shield volcanoes, in contrast, are built almost entirely of fluid lava flows in all directions. In northern California and Oregon, these huge structures may have diameters of 3 or 4 miles and heights of 1.500 to 2.000 feet.
Mauna Loa, the world’s largest active volcano, projects 13,677 feet above sea level, topping out at 28,000 feet above the deep ocean floor. The Hawaiian Islands were created by linear chains of this type of eruption.
In some shield volcano eruptions, basaltic lava (hard, dense dark volcanic rock) seeps from long fissures in the vent and forms lava plateaus like those in southeastern Washington, eastern Oregon, and southern Idaho. Lava flows more than one mile in thickness may be observed along the Snake River in Idaho.
Lava domes
Lava domes grow by expansion from within as a result of lava too viscous to flow any great distance. The lava just piles up and around the vent. Domes commonly occur in piggyback fashion within craters of large composite volcanoes.
Lassen Peak and Mono domes in California are examples. Lava domes can be deceptively peaceful. In 1902, the eruption of Mount Pelee, with an accompanying 100-mph flow of ash, incandescent gases, and volcanic dust, took the lives of 30,000 persons.
Submarines
In the shallow open ocean, violent steam-blast eruptions can occur. Uninhibited by the water pressure existing at great depth, volcanoes remarkably similar to those on land may spout tremendously explosive emissions as a result of violent interaction between hot lava and seawater.
The famous “black sand” beaches of Hawaii were created in such a fashion.
Geysers, fumaroles, and hot springs are located in areas of young volcanic activity.
Geysers form when surface water percolates downward into high-temperature regions adjacent to a magma reservoir, is heated, and then shot back to the surface through fissures and cracks in the surface.
Fumaroles (solfataras) emit mixtures of steam and other gases, which include sulfur.
Hot springs vary in temperature in view of how much heat is supplied by inter-section with the subsurface thermal area and to what degree the heated water is then diluted by cool groundwater nearer the surface.
At-Risk
There are more than 500 active volcanoes in the world, 50 of which are in the United States. An active volcano is one that has erupted at least once within recorded history.
Most active volcanoes are located along or near the margins of the Earth’s continents. More than half border the Pacific Ocean and are known as the “Ring of Fire.”
Plate Tectonics
It is generally accepted theory that there is a relationship between the location of volcanoes and the nature of the Earth’s surface, which is broken into a number of shifting, slipping slabs or plates that measure 50 miles thick.
As the plates move, they are vulnerable to pressure buildups along their borders. Plate movement is being researched, with the intermediate conclusion that all plates do not move alike. Some rotate like huge Lazy Susans between other structures.
Volcanoes, also, do not always seem to erupt through the seams of these plates. The Hawaiian Islands seemed to have been formed by a “hot spot,” burning its way many times through the middle of a north-western-moving Pacific plate as it passed.
Many of the volcanic sites in the north-western U.S., however, are near the intersection of plates.
Hazard Assessment
The U.S. Geological Survey’s Volcano Hazards Program, stimulated by tragedies at Mount St. Helens, considers 33 volcanoes in the U.S. “potentially active and likely to erupt in the future.”
The USGS monitors all signs of volcanic activity and assesses potential dangers. Monitoring Mount St. Helens serves as a model for detecting possible eruptions elsewhere. This process includes measurement of changes in the surface, investigation of earthquakes generated beneath the volcano and study of changes in gas emissions accompanying the underground movement of magma.
Measurement
Shortly after the Mount St. Helens blast, geologists reestablished a surveying network to chart the changes instrumental to the prediction of further eruptions. They looked for telltale bulges that mean the magma is swelling to dangerous levels inside the vent of the volcano.
Using electronic distance meters and other equipment, they plotted against a time base the displacement of ground cracks, thrust faults, and dome growth. A gradual change that began to accelerate became the basis for relatively long-term predictions.
Both ground cracks and thrust faults develop continually before eruptions, and the crater floor begins to tilt. An electronic device called a tiltmeter was helpful in predicting 1981-82 eruptions. Lava dome measurement for those “telltale bulges” also provided a meaningful predictor of activity: expansion moving at roughly 2 centimeters per day increased to about 200 centimeters per day the day before a May 14, 1982 eruption.
Earthquakes
Earthquakes and volcanoes are related. Scientists are learning to identify the patterns of earthquake activity that precede and accompany the volcanic activity.
Four major types of seismograms have been recognized at Mount St. Helens:
- Deep earthquakes and those located away from the volcano which produces high-frequency signatures and sharp arrivals;
- Shallow earthquakes less than 3 kilometers under the dome;
- Surface events such as rockfalls and avalanches
- Harmonic tremor, a long-lasting rhythmic signal often associated with active volcanoes.
Seismic monitoring has been helpful in making predictions but is still not fully understood. Research is proceeding.
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Gas Emission
Studies of how various gases relate to eruptive styles may provide a basis for protecting the public. It has been noted that increased rates of sulfur dioxide emissions occur when a batch of magma rises toward the surface. Changes in hydrogen concentration are also thought to be a significant predictor.
Other Sites
Survey networks and tilt stations have been established on other volcanoes in the Cascade Range:
- Mount Baker and Mount Rainier in Washington
- Mount Hood and Crater Lake in Oregon.
- and Mount Shasta and Lassen Peak in Northern California.
Measurement of these peaks occurs at 3-year intervals unless there is a reason to measure events more frequently. Earthquake monitoring is continuous. The Long Valley-Mono Lake area near Mammoth Lake, California, is under observation because signs of fresh magma intrusion have been detected, bulging upward at least 13 inches from the caldera floor in the five years.
Computers
Along with all this monitoring and research, various data bank computers have made some disconcerting connections between the length of time a volcano has been quiet and the explosiveness of its eruption. The most destructive and highest casualty explosions have the greatest intervening time intervals.
Effects of destructive volcanoes
In addition to the obvious primary effects of an explosion or lava flow, there are widespread results that include the destruction of vegetation, mudflows and the weather.
The original Mount St. Helens catastrophe stripped trees from most hill slopes within 11 kilometers north of the volcano and leveled nearly all vegetation as far as 20 kilometers in a 180-degree arc north of the mountain.
Volcanic debris deposited in rivers increased the chances of flooding, as did mudflows. A debris avalanche covered a nearby valley floor with up to 180 meters of assorted volcanic products.
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The U.S. Army Corps of Engineers was called in to reduce the chances of flooding. Scientists are also studying the effects of volcanic eruptions on the weather and on other phenomena such as the El Nino warming effect, particularly in terms of sulfur dioxide in the atmosphere. Some say there is a clear relationship between eruptions and colder weather: others believe there are too many variables to create a pure cause-and-effect relationship.
The American Lung Association is concerned about the effects of volcanic ash, particularly on persons with vulnerable respiratory systems. Special focus was the threat of cristobalite in the ash, hard particles of which, inhaled over a long period of time, can cause silicosis.
This disability includes breathing problems, weight loss, fever, and coughing. The Washington Lung Association urged people in fallout areas to wear face masks when forced to move around in the dust.
Precautions
Even with all the research and monitoring that is being conducted on volcanic eruptions, no one has all the answers. If you are in an emergency caused by such an eruption or pending eruption, follow the directions of authorities.
Do not attempt to approach the activity more closely than advised. If you live in a volcanic area, be aware of any developing volcanic activity. Familiarize yourself with emergency procedures and routes. In short, a survivalist should know when and how to evacuate.
Potential destructive volcanoes in the United States:
Alaska
- Augustine Volcano
- Aleutian Volcanoes
- Iliamna Volcano
- Katmai Volcano
- Mount Spurr
- Mount Wrangell
- Mount Edgecombe
- Redoubt Volcano
Arizona
- San Francisco Peak
California
- Clear Lake Volcanoes
- Coso Volcanoes
- Lassen Peak
- Long Valley Caldera
- Medicine Lake Volcano
- Mono-Inyo Craters
- Mount Shasta
Hawaii
- Haleakala
- Hualalai
- Kilauea
- Mauna Loa
New Mexico
- Socorro
Oregon
- Crater Lake
- Newberry Volcano
- Mount Jefferson
- Mount Hood
- Mount McLoughlin
- Three Sisters
Washington
- Mount Baker
- Mount Adams
- Glacier Peak
- Mount Rainier
- Mount St. Helens
Wyoming
- Yellowstone Caldera
Concluding
Volcanoes are a real danger that can turn our world upside-down. We rarely think about the dangers of volcanoes as most people are uninformed, and they are unaware of what living near volcanoes means.
If we look at historical events such as the Krakatoa explosion, we will all acknowledge that a volcanic eruption is a destructive event that we cannot escape from. This informative article provides you with essential information and allows you to research this topic further if you so wish.
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