How do volcanoes affect the atmosphere and climate?

This photo shows the large white billowing eruption plume from Rabaul being carried in a westerly direction by the weak prevailing winds. At the base of the eruption column is a layer of yellow-brown ash being distributed by lower level winds. A sharp boundary moving outward from the center of the eruption in the lower cloud is a pulse of laterally-moving ash which results from a volcanic explosion. Image taken on 09/29/94 from STS-64 (STS64-116-064). Information Source: Shuttle Images at the Johnson Space Center in Houston, Texas.

To get into the scientific literature read chapter 17 of Peter Francis' excellent new book, "Volcanoes - A Planetary Perspective." The 33 references give you the important articles from Ben Franklin to the early 1990s. Good reading!

Chuck Wood

There are two things to think about. The first is how the weather near an erupting volcano is being affected. The second is how large eruptions will affect the weather/climate around the world. I think more people are worried about the second issue than the first.

As far as I know, the main effect on weather right near a volcano is that there is often a lot of rain, lightning, and thunder during an eruption. This is because all the ash particles that are thrown up into the atmosphere are good at attracting/collecting water droplets. We don't quite know how the lightning is caused but it probably involves the particles moving through the air and separating positively and negatively charged particles.

Another problem that we are having here in Hawai'i involves the formation of vog, or volcanic fog. The ongoing eruption is very quiet, with lava flowing through lava tubes and then into the ocean. Up at the vent is an almost constant plume of volcanic fume that contains a lot of sulfur dioxide. This SO₂ combines with water in the atmosphere to form sulfuric acid droplets that get carried in the trade winds around to the leeward side of the Big Island. The air quality there has been really poor since the eruption started in 1983 and they are getting pretty tired of it.

As for the world-wide affects of volcanic eruptions this only happens when there are large explosive eruptions that throw material into the stratosphere. If it only gets into the troposphere it gets flushed out by rain. The effects on the climate haven't been completely figured out. It seems to depend on the size of the particles (again mostly droplets of sulfuric acid). If they are big then they let sunlight in but don't let heat radiated from the Earth's surface out, and the net result is a warmer Earth (the famous Greenhouse effect). If the particles are smaller than about 2 microns then they block some of the incoming energy from the Sun and the Earth cools off a little. That seems to have been the effect of the Pinatubo eruption where about a 1/2 degree of cooling was noticed around the world. Of course that doesn't just mean that things are cooler, but there are all kinds of effects on the wind circulation and where storms occur. Some folks think that large eruptions can cause the weather phenomena called "El Nino" to start. This is a huge disruption of the Earth's atmospheric circulation. The connection hasn't been accepted by everybody though.

An even more controversial connection involves whether or not volcanic activity on the East Pacific Rise (a mid-ocean spreading center) can cause warmer water at the surface of the East Pacific, and in that way generate an El Nino. Dr. Dan Walker here at the University of Hawai'i has noticed a strong correlation between seismic activity on the East Pacific Rise (which he presumes indicates an eruption) and El Nino cycles over the past ~25 years.

Scott Rowland

CO₂

Dr. Don Thomas, University of Hawai`i

Painting of Mount Vesuvius

Volcanoes affect people in many ways, some are good, some are not. Some of the bad ways are that houses, buildings, roads, and fields can get covered with ash. As long as you can get the ash off (especially if it is wet), your house may not collapse, but often the people leave because of the ash and are not around to continually clean off their roofs. If the ashfall is really heavy it can make it impossible to breathe.

Lava flows are almost always too slow to run over people, but they can certainly run over houses, roads, and any other structures.

Pyroclastic flows are mixtures of hot gas and ash, and they travel very quickly down the slopes of volcanoes. They are so hot and choking that if you are caught in one it will kill you. They are also so fast (100-200 km/hour) that you cannot out-run them. If a volcano that is known for producing pyroclastic flows is looking like it may erupt soon, the best thing is for you to leave before it does.

Some of the good ways that volcanoes affect people include producing spectacular scenery, and producing very rich soils for farming.

Scott Rowland

Gases

Gases pose the greatest hazard close to the vent where concentrations are greatest. Away from the vent the gases quickly become diluted by air. For most people even a brief visit to a vent is not a health hazard. However, it can be dangerous for people with respiratory problems.

The continuous eruption at Kilauea presents some new problems. Long term exposure to volcanic fumes may aggravate existing respiratory problems. It may also cause headaches and fatigue in regularly healthy people. The gases also limit visibility, especially on the leeward side of the island where they become trapped by atmospheric conditions.

Source of Information:
Volcanic and Seismic Hazards on the Island of Hawaii by Christina Heliker, 1991, U.S. Geological Survey General Interest Publication.

Steve Mattox

The biggest eruption

Lava flows covering the Kamoamoa area of Hawai`i Volcanoes National Park. Photograph by Steve Mattox, November 14, 1992.

Plants are destroyed over a wide area, during an eruption. The good thing is that volcanic soil is very rich, so once everything cools off, plants can make a big comeback!

Livestock and other mammals have been killed by lava flows, pyroclastic flows, tephra falls, atmospheric effects, gases, and tsunami. They can also die from famine, forest fires, and earthquakes caused by or related to eruptions.

Mount St. Helens provides an example. The Washington Department of Game estimated that 11,000 hares, 6,000 deer, 5,200 elk, 1,400 coyotes, 300 bobcats, 200 black bears, and 15 mountain lions died from the pyroclastic flows of the 1980 eruption.

Aquatic life can be affected by an increase in acidity, increased turbidity, change in temperature, and/or change in food supply. These factors can damage or kill fish.

Eruptions can influence bird migration, roosting, flying ability, and feeding activity.

The impact of eruptions on insects depends on the size of the eruption and the stage of growth of the insect. For example, ash can be very abrasive to wings.

Sources of Information:
Blong, R.J., 1984, Volcanic hazards: A source book on the effects of eruptions: Academic Press, Orlando, Florida, 424 p.

Del Moral, R., 1981, Life returns to Mount St. Helens, Natural History, v. 90, no. 5, p. 36-46.

Steve Mattox

How quickly do plants begin to grow back? The answer is that it depends on how much rain falls in the particular area. For example, on the rainy side of the island of Hawai'i, flows that are only 2 years old already have ferns and small trees growing on them. Probably in 10 years they'll be covered by a low forest. On the dry side of Hawai'i there are flows a couple hundred years old with hardly a tuft of grass in sight. This means that when you are looking at old lava flows and trying to determine how old they are based on the amount of vegetation, you have to take the climate into effect as well.

Scott Rowland

Long term effects

It is usually the short-term effects that are really bad. For example, there was a very big eruption of Santa Maria volcano (Guatemala) in 1902. The eruption itself killed a few hundred to perhaps 1500 people as well as thousands of birds. Pretty soon there were so many insects including disease-carrying mosquitoes that eventually 3000-6000 people died from malaria. (This information came from Volcanoes of the World, by Tom Simkin and Lee Seibert).

Scott Rowland

Extinction of Dinosaurs

Anyway, if you have enough large explosive eruptions, then the theory says that there will be enough ash in the stratosphere to have one of these effects. You need an eruption (or series of eruptions) that is much bigger than anything we have ever witnessed. The reason that you need to put the ash into the stratosphere is that if it is only in the troposphere (where weather clouds are), then it will get rained out very quickly and it won't be around long enough to have a climatic effect.

Of course the more famous idea is that a huge meteorite came in and hit the earth, throwing up enough gas and dust into the stratosphere to have the same heating or cooling effect. One line of support for this is that at the geologic time boundary where the dinosaurs died out (the Cretaceous-Tertiary boundary) there is a layer of clay that is rich in an element called iridium. Iridium is not very common on Earth, but it is proposed to be more abundant in asteroids and meteorites. One way to produce such a layer at the same instant that the dinosaurs died out is therefore to have a meteorite bring it in.

One major problem with the volcanic hypothesis is that volcanoes, especially the explosive ones, don't produce much iridium. Basaltic volcanoes, such as those here in Hawai'i produce more iridium but they are not very explosive.

A more recent idea that tries to get around these problems is that instead of a huge explosive eruption, you have a long-term basaltic eruption that mainly puts SO₂ gas into the troposphere. The gas will be converted into small droplets of sulfuric acid which will block incoming sunlight. Because it is only in the troposphere much of the acid may get rained out, but if you have an eruption that continues long enough it can keep up with the rain to produce an Earth-covering haze.

What kind of eruption might this be? There are places on Earth where huge volumes of basaltic lavas are found. They are called flood basalts, and the most famous are the Columbia River Basalts in Washington/Oregon, and the Deccan Traps in India. The name "flood basalts" gives an indication of how most people consider them to be erupted, namely as huge fast-moving floods of basalt. However, recent work by a number of scientists here at the University of Hawai'i (including Steve Self, George Walker, Thorvaldur Thordarson, and Sarah Finnemore) have shown that these flood basalts look more like the slow-moving type of basalt lava (pahoehoe) than the fast-moving type ('a'a). This leads next to the conclusion that perhaps these flood basalts were not emplaced as huge floods in short periods of time but rather as slower-moving flows over a long period of time (such as 1-2 hundred years). The eruptions would still have been much bigger than those we see here in Hawai'i, however.

This new idea thus provides a long-term source for lots of SO2, and a possible explanation for the iridium (which, again, is found in basalt lava). It wasn't the Columbia River Basalts that were the cause for the dinosaur extinction because the dinosaurs disappeared about 65 million years ago, and the Columbia River Basalts are only about 12 million years old. Perhaps it was the eruption of the Deccan traps, since their age is about right.

Scott Rowland

Aso viewed from the visitors center. Small plume above Aso during a period of mild Strombolian eruptions, December 30, 1991. Photograph by Mike Lyvers.

That's a good question. I guess the main good effect that volcanoes have on the environment is to provide nutrients to the surrounding soil. Volcanic ash often contains minerals that are beneficial to plants, and if it is very fine ash it is able to break down quickly and get mixed into the soil.

Perhaps the best place to look for more information about this would be to look up references about some of the countries where lots of people live in close proximity to volcanoes and make use of the rich soils on volcanic flanks. These would include Indonesia, The Philippines, Japan, Italy, etc.

I suppose another benefit might be the fact that volcanic slopes are often rather inaccessible, especially if they are steep. Thus they can provide refuges for rare plants and animals from the ravages of humans and livestock.

Finally, on a very fundamental scale, volcanic gases are the source of all the water (and most of the atmosphere) that we have today. The process of adding to the water and atmosphere is pretty slow, but if it hadn't been going on for the past 4.5 billion years or so we'd be pretty miserable.

Scott Rowland

Volcanoes have done wonderful things for the Earth. They helped cool off the earth removing heat from its interior. Volcanic emissions have produced the atmosphere and the water of the oceans. Volcanoes make islands and add to the continents.

Steve Mattox

Pros and Cons of Volcanoes

Pros
Create new islands and land.
Provide habitat to pioneer species.
Create economic mineral deposits.
Create beautiful landscapes.
Generate tourism.

Cons
Destroy old habitat and crops.
Destroy cities, towns, communities.
Displace populations.
Kill people and other animals.
Disrupt commerce.
Generate tsunami.

Steve Mattox

The Hawaiian Volcano Observatory was established in 1912 by Dr. Thomas Jaggar of the Massachusetts Institute of Technology. The observatory is managed the U.S. Geological Survey. Photograph by J.D. Griggs, U.S. Geological Survey, October 23, 1986.