1. Effects of Volcanoes on Climate

 Volcanoes and How They Effect the Climate

  Volcanoes have, for millions of years, effected the climate of earth in many different ways. This site is designed to show you how some of those mechanisms work.

  A volcano is any mountain on the earth's surface that has a vent through which things like lava, ash, and gases are emmitted in order to relieve pressure underneath the earth's surface.  There are many different types of volcanoes and they are all catagorized by their shape and the type of tephra (or volcanic material) that they produce.

  Despite many of the things we often hear about volcanoes, there are many good effects that they have on the earth. On of those effects is the
production of very nutrient rich soil. As the ash, which is often very fine, is distributed on the ground, it is broken down and absorbed very easily by the soil.  Since this process takes place so quickly and easily, the soil that absorbs it becomes nutrient rich very quickly.  One way that scientists can tell how old a particular lava flow is, is bylooking at the type of vegetation that has grown over that flow.  They have to take into account the climate of the area as well as the quality of the soil to determine the flow's age.  For example, some flows in Hawaii begin to have ferns and small trees growing on flows that are only 2 years old.

  Another benefit that the earth receives from volcanoes is the atmosphere itself.  As the earth was forming it was cooling very rapidly.  This cooling caused shrinking and thus a great deal of pressure. Cracks in the surface were able to allow some different types of material to escape to relieve that pressure. Some of that material was gases of varying kinds, including water.  As this process took place over the following 4.5 billion years, the atmosphere and all of the water on the earth's surface was able to take the form we know today.

  Something else that can be viewed as a good effect of volcanoes is the spectacular sunsets that they can produce. If a volcanic explosion is large enough to propell ash and debris into the stratosphere, there can be amazing sunsets for the weeks to come.  These are mainly caused by the sulfuric acid aerosols.  These aerosols must make it all the way into the stratosphere, however. If they are only in the troposphere, they will be washed out of the atmosphere by the rain and dissipate too quickly.

  Most of the effects that we associate with volcanoes are the destructive and devistating things that we hear on the news. Most common to all
volcanoes is the burial of nearby (and sometimes not so nearby) things by lava, ash, or mud.  These products of a volcano can cause large amounts of
devistation all by themselves.  They can kill plants and animals instantly or smother them out over a slightly longer period of time.

  An invisible force to be reckoned with for some volcanoes is a phenomenon known as pyroclastic flows.  These are flows of toxic gases that roll down the side of the volcano.  They move so fast (at speeds of 200 km/hr0 that once they start, there is no way to out run them.  It is believed that there are some volcanoes that are more prone to this type of activity so if one of those volcanoes is showing signs that it may errupt,officials will evacuate the area immediately. An example of apyroclastic flow occurred during the last erruption of Mount St. Helens. According to the Washington Department of Game and Wildlife, many animals died as a result of that pyroclastic flow. Among them were 11,000 hares, 6,000 deer, 5,200 elk, 1,400 coyotes, 300 bobcats, 200 black bears, and 15 mountain lions.

  Another effect that scientists are just begining to study is that of rain nd lightening during erruptions.  The ash that is ejected into the air acts as a magnet for water vapor and gives those droplets something to nucleate on.  That will lead to the rainfall experienced during an explosion.  As for the lightening, it is thought that as the ash is shot into the air, it goes fast enough to seperate the positive and negative charges in the air, thus causing the lightening. This idea is still being researched, however.

  Two other related effects of volcanoes are acid lakes and "vog". Some of the usual gases released during an erruption are H2O, CO2, and SO2.  These gases can all undergo a chemical reaction with one another to form carbonic acid and sulfuric acid.  If the water that is involved in the reaction is in the gaseous state, it can lead to "vog" or volcanic fog. If a person lives downwind from an area where vog is produced, it can create conditions that are very difficult to breathe in, especially if the person already has an underlying respiratory condition.  If the water that reacts is in the aqueous or liquid state, it can create an acid lake.  This occurs anywhere this acidic water collects, often in craters formed by the expolsion.  The water can be very acidic here and can even have a pH of less than one!

  People do not have to be caught in an erruption to be effected by it. For example, in 1815 in Indonesia, a volcano named Tambora errupted. In the initial blast 10,000 people were killed. as deadly as that was, another 80,000 people were killed by famine and disease due to crop loss and livestock loss.

  A world wide effect of volcanoes is the warming and cooling of the earth. This is not caused as much by the greenhouse effect as one might think, but more by the size of the ash ejected by a volcano.  Warming takes place when the particle from the volcano are larger than 2 microns. That size tends to block outgoing radiation and makes the surface of the earth warmer.  Cooling is produced when the particles are smaller than 2 microns, a size that tends to block incoming radiation.  The size of the particle is important, because it must be the size of the wavelength or smaller to effect a wave.

  This leads us to a well known theory called the Dinosaur Extinction Theory. The idea behind this theory is that a very large volcanic erruption caused either warming or cooling to enough of a degree that either the dinosaurs themselves could not survive, or their food chain was somehow disrupted. People who agree with this theory say that around the time of the extinction of the dinosaurs, a relatively large layer of iridium was laid down. This layer could have been caused by a type of volcano called a basaltic volcano.  Basaltic volcanoes ahve a higher iridium content than other types of volcanoes. If there were a huge continuous erruption, this layer could have been produced and there is possible evidence of this in the Deccan Traps ( a flood basalt in India) that occured at around the same time as the extinction of the dinsaurs.

  The people who disagree with this theory also acknowledge the layer of iridium, but belive that much iridium could not be produced by anything on earth, so it must have come from a large meteor striking the earth, and depositing this iridium layer.  There is also possible evidence of this theory near the Gulf of Mexico, where it is believed that a large crater from this meteor exists.  Both sides of this thoery are still being explored.

  As you can see, there is still a great deal of research to be done on this topic.  Many of the related theories are still topics of hot debate. Since we have only looked at the earth's volcanic activity for such a short period of time, many things are still left undiscovered. Scientists are not daunted by this, however.  For them it means great job security!

For any questions on volcanoes a great site to link to is http://www.volcanoes.com/
 

3. Mt. Pinatubo

http://www.geo.mtu.edu/~mtdolan/pinatubo/volcano/plume1.gif

This picture was taken at 8:51 on June 12, three days before the major eruption.  This ash cloud reached an elevation of 19,000 meters above sea level.

http://eospso.gsfc.nasa.gov/eos_edu.pack/p37.html

The first picture is a graph of the optical depth for a wavelength of 1020nm over the surface of the earth for about a month and a half before the major Mt. Pinatubo erruption on June 15, 1991.

The second picture is a graph of the optical depth for a wavelength of 1020nm over the surface of the earth for a period one day before the eruption on June 15,1991 till July 26, 1991.  This graph shows that the Pinatubo aerosals have spread around the globe at the equator.

The third picture is a graph of the optical depth for a wavelength of 1020nm over the surface of the earth for the period of February 13, 1993 (approximately 1 year, 8 months after the eruption) through March 26, 1993.

http://eospso.gsfc.nasa.gov/eos_edu.pack/p35.html
 These images show the spread of the sulfur dioxide gas cloud during a period of June 17-19, 1991. That's from just 2 days after the eruption to 4 days after.

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960724/ob960724.html
Here is a 15-frame movie of the spreading of the sulfur dioxide cloud between June 16 and June 30, 1991.
 
 

2. Mt. Tambora

The eruption of Mount Tambora, in 1815, is the largest eruption in our recorded history.  It scored a 7 on the Volcanic eruptions Index, the only eruption in recorded time to do so.  It erupted so much ash into the atmosphere that localities within six hundred kilometers remained darkened for over two days.  Some estimate that between 40 and 90 cubic kilometers of material were injected into the atmosphere and fell out during the following week in a circular area of 400 km in diameter.  In Java, 550 miles away, one centimeter of ash fell.  At the end of all this, Mount Tambora was only two-thirds it's original height.
    10,000 people died in the original blast, from bomb impact, tephra fall and pyroclastic flows, as well as, wild winds and large pumice rocks falling from the sky.  But an estimated 92, 000 people died in total, the other 82,000 were killed by disease and starvation, as most of the crops in the area were destroyed.
    Tambora also had many global affects.  The following year, 1816, was deemed "the year without a summer."  Daily minimum temperature were abnormally low that year.  Famine was rampant due to crop failure.  London complained of a persistent dry fog.  The sun was so dimmed that sunspots could be seen with the naked eye.
    The most violent eruption in the history of the United States is the one at Mount St. Helens.  In comparison with the eruption of Tambora, it is a very tame eruption.  Only 57 lives were lost, and most of these by people who either took unnecessary risks or refused to evacuate in time.  There was a lot of damage to roads, timber and the wildlife.  It also had some interesting side aspect that are different from the larger eruptions.  For example, the light dusting of ash sealed moisture into the soil which resulted in a bumper crop for apples and wheat.
    In the end, all eruptions will feel very destructive to the people who live around them.  The interesting part, is that many are hardly violent at
all when compared to other eruptions in our recent past.  It is, simply put, important to study these eruptions, so we can be as prepared as possible for any really large eruptions in out future.

3. Mt. Krakatoa

I studied the climatic effects of the 1883 eruption of Krakatoa, a volcanic island that lies in the Sundra Strait between the islands of Java and Sumatra in Indonesia.

 On August 27, 1883 Krakatoa erupted, marking one of the most violent volcanic eruptions ever recorded in world history.  The eruption was heard thousands of kilometers away and was so powerful that it obliterated the island of Krakatoa, so that 75% of the island no longer exists.  Krakatoa ejected the equivalent of 20 cubic kilometers of rock into the atmosphere, sending a column of smoke and ash 26 kilometers into the stratosphere, where the particles have a long residence time.  In comparison, the eruption of Mt. Saint Helens emitted only one cubic kilometer of ash.
 Due to their weight, the ash particles settle down to the ground in a matter of days.  The ash particles have a low residence time because they remain in the troposphere.  The sulfer gases emitted by the volcano combine with traces of water vapor in the atmosphere to form tiny sulfuric acid aerosols.  These aerosols have a much longer residence time (a year or two) because they are injected into the stratosphere.  The eruption of Krakatoa resulted in 294 million tons of sulfuric acid in the atmosphere.

 Large volcanic eruptions such as Krakatoa cause a temporary global cooling effect.  The earth cooled by about 2.5 degrees Celsius for one to two years after the eruption of Krakatoa.  This is due to the amount and small size of the aerosols in the atmosphere.  As efficient reflectors of sunlight, aerosols screen the ground from some of the solar radiation it would ordinarily receive from the sun.  Thus when there is an excess of volcanic particles and aerosols in the atmosphere, they have a cooling effect on the earth.  This was the case in Krakatoa which, in the year following the eruption, experienced its coolest year ever recorded.

 In addition the area also experienced brilliant red sunsets throughout the following year due to the presence of aerosols in the atmosphere.  The aerosol particles produce the vivid sunset colors by promoting scattering among the particles or the reflection of sunlight in all directions. According to our text book, the scattering of small particles depends on the wavelength of solar radiation and at sunset, the sunlight travels farther through a thicker portion of the atmosphere. The promotion of sunlight reflection results in the enhanced sunset coloring.

 The eruption of Krakatoa also created great tidal waves reaching 120 feet in height.  These subsequent tsunamis were reported as far away as South America and Hawaii and were responsible for the destruction of 150 villages and took more than 30,000 lives.  Finally in 1930, Anak Krakatoa (which means child of Krakatoa in Indonesian) emerged from the sea resulting from the 1883 eruption.