Active Volcanoes in the United States
A volcanologist discusses the "dangerous" Mount Rainier of the Pacific Northwest, and others in the U.S. and around the world.
- Grades: 3–5, 6–8, 9–12
Expert volcanologist Dr. Stanley Williams shared answers to the following questions with Scholastic Network.
What were the Mount St. Helens eruptions like?
I was not at Mount St. Helens the day of the May 18 eruption because I was back in classes in New Hampshire. I have looked many times at the photos and it was an awesome eruption, with the ashes being carried in a column to 27 kilometers above the surface of the earth. Friends of mine who lived in Montana, Wyoming, and Colorado had ash raining down on their yards the next day because they were being carried by the wind above where jets can fly. However, I know that the Mount St. Helens eruption was not really big compared to the others which we have studied. It released about one cubic kilometer, but Long Valley of California released 500 cubic kilometers about 700,000 years ago.
Is Mount St. Helens still active?
Mount St. Helens is still active, with the new dome that covers the vent from which the 1980 eruption came growing slowly. It has had a few small explosions in the 1990s but they get smaller and less frequent with time. Most volcanoes that have an eruption like Mount St. Helens will remain active for about a decade.
How deep is Mount St. Helens'core?
When we talk about the interior of a volcano, we usually don't talk about things like the core. To a geologist, the core is the center of the earth, a very different idea. Beneath and inside a volcano is the magma chamber, a zone where the molten rock (magma) is sitting. At Mount St. Helens, there are good ideas of where that is — at between 7 and 14 kilometers in depth. We know that because of where there are almost no earthquakes, and that is a special thing for molten rocks — they can't break and make earthquakes.
Are people in danger of Mount Rainier and other Pacific Northwest volcanoes exploding?
Rainier is one very dangerous volcano because about two million people live on the top of old deposits of mudflows from previous eruptions. That type of eruption is what killed 25,000 people in 1985 in Colombia. There are other active volcanoes in the Cascade volcano chain of the western U.S.
Is there any chance that the "extinct" San Francisco peaks may erupt some day?
The San Francisco peaks are an active volcano, not extinct. That word extinct is basically a very dangerous one. Many of the worst eruptions of history have happened on extinct volcanoes! It is just that humans do not look at long periods of time that volcanoes are active in. There are about 400 small cinder cones around Flagstaff, with Sunset Crater being the most recent. It erupted in about A.D. 1100. The good news is that cinder cones are usually what we call "monogenetic," meaning that they only erupt once (for about ten years). I am not going to move to Flagstaff and wait for the next eruption because it probably won't happen in my lifetime. The record tells us that the San Francisco peaks have not had activity for a long time and the cinder cones seem to be less frequent than they were before.
What can you tell us about the volcanoes in Japan?
Japan is a really interesting place for volcano information. There are about 40 volcanoes in Japan and many of the big eruptions of the world have happened in that country. One of the reasons that the Japanese are such leaders in volcanology is that they have such a long record. Also, the Japanese population is about half the size of the U.S., but they all live amongst volcanoes in a country about the size of our state of California. The islands have earthquakes like California and like the special earthquakes that happen beneath and around volcanoes. So, it is really a hopping place to live. The Japanese are very respectful of their environment, know that they cannot stop volcanoes from erupting (a regular question that I get), and try to monitor the activity and mitigate the hazards. That means teaching people how to handle the eruptions without panic. The Japanese government and universities have created about 18 volcano observatories — places where scientists can continue to monitor volcanic activity and study older deposits.
Fuji is the most famous volcano of Japan, and it has erupted more than 50 times that we know of. The most recent very bad eruption was in 1707, when ash rained on a large area, including Tokyo. It is almost certain that Fuji will erupt again. Sakurazima has been erupting almost constantly since the early 1950s. Many people live next to it and they just put up with it as a part of life. The kids wear hard helmets to school for safety, and an observatory has many instruments monitoring it each day. That makes it a valuable resource to all of us because of the very information that they have obtained.
What is Izalco?
Izalco was called the "Lighthouse of the Pacific," with continuous eruptions for about 200 years, since it was first created in 1769. It is now quiet. Inside the crater of a volcano is a very special place — with very hot gas roaring out of small holes (fumaroles) in the crater and beautiful minerals being deposited from the gas.
What is Tavurvur?
Tavurvur is the name of a volcano in Papua New Guinea which had an important eruption in September 1994. I was there because we thought that it was going to turn into one of the most important and largest of this century. It stopped before reaching that level of volume of ash erupted. Tavurvur erupted until the end of December 1994. Its ash rained down on the city of Rabaul and was so heavy that it made the roofs of most of the houses collapse. It could have caused many thousands of people to die, but the people were ready and evacuated themselves. Only five people died. We are very happy to have an example of where normal people could be trained in how to handle an eruption, without terrible panic. We need to learn more about how to teach people about the volcanoes that they live close to.
Can you tell me about Erebus?
Erebus is kind of special because of its unique chemistry and its lake of lava splashing around. It actually throws big crystals out, sort of like popping popcorn, when it is more active. All volcanoes release gases (like water, carbon dioxide, sulfur dioxide, and hydrogen chloride) which contribute to worldwide pollution. Erebus does not release a great deal of gases, so it is not too important.
How many volcanoes are there in Hawaii?
Hawaii, the Big Island, has five different volcanoes on it. Two of them, Kilauea and Mauna Loa, erupted together in 1984.
What is the "Ring of Fire"?
The Ring of Fire is at the edge of the Pacific Ocean and is called that because of the many volcanoes which lie close to the coastline of almost all of the countries that are around the Pacific. There are about 1,500 known active volcanoes in the world and about 1,000 of them are around the Ring of Fire. The reason for all of the volcanoes is what we call Plate Tectonics theory. We think that the earth is covered by thin, strong plates, sort of like the strong shell of an egg. The earth is not dead; the plates move around and are being formed all of the time. However, the earth is not growing in size, so the new plates must be consumed some place, and that is what is happening at the rim of the Pacific.
The new crust happens in the ocean, so deep that we do not see it. It moves toward the continents, where the crust is pushed down beneath the giant land masses. We call that subduction. The plate gets so deep that it melts at about 150 kilometers inside the earth. The magma (molten rock) is light, so it rises toward the surface and some of it erupts. That is the origin of a volcano and its continuing eruptive activity. The islands of Hawaii and their volcanoes are very different because they are not near a coastline. They are in the middle of a plate in the ocean. They are caused by a "hot spot" in the mantle or deep layer within the earth. There is a line of many Hawaiian islands because the hot spot is sort of sitting still, as the plate moves over it.
Were there ever any volcanoes in the state of New Jersey?
New Jersey did have volcanic eruptions. About 200 million years ago — recent for a geologist! There are very nice volcanic rocks near Newark that were formed as the ancient Atlantic Ocean (the one before the one we now look at) was being formed by the split between North America and Europe.
Were there ever any volcanoes in Michigan?
Yes, there were volcanoes in the Upper Peninsula. It was a long time ago — 2.5 billion years! The copper mines of the Upper Peninsula are there because of the ancient volcanoes'putting out huge lava flows and minerals.
Does the Midwest have a lot of volcano action?
There are no active volcanoes in the Midwest, sorry. The center of the United States is old and very stable, so it is hard to find even ancient volcanoes. A good place is Missouri, where the Saint Francis Mountains contain some beautiful volcanic rocks of about a billion years ago.