Why are Scientists Interested in Volcanoes?

Scientists are interested in volcanic eruptions and clouds because:

Volcanoes are sources of natural pollution.
Volcanoes emit gases that affect the health of humans and animals.
Climate can also be affected by volcanic eruptions and gases.
Volcanoes provide insight into the inner earth.
Volcanoes may have controlled human genetic development.

Types of Volcanic Gases and Their Effects

The most abundant volcanic gases that are released into the atmosphere are water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). Gases that are released in smaller amounts include hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL), hydrogen fluoride (HF), and helium (He).

How Do Volcanic Clouds Affect the Atmosphere?

What is Vog?

Vog is an abbreviation for volcanic smog which is created when sulfur dioxide (SO2) and other volcanic gases chemically combine and interact in the atmosphere with oxygen, dust, moisture and sunlight over a time period from minutes to days. Vog appears as a visible haze that consists of gas plus a suspended mixture of tiny liquid and solid particles, called aerosol. Sulfuric acid and other sulfate compounds are the main components of the aerosol in vog.

How Do We Measure the Climatic Effects of Volcanic Eruptions?

There are two main indeces used to assess the effects of volcanic eruptions on climate. They are the Dust Veil Index (DVI) and the Volcanic Explosivity Index (VEI). The Dust Veil Index (DVI) is based on estimations of the amount of material dispersed into the atmosphere as well as the temperatures at and amount of sunlight reaching the Earth's surface. This index is unfortunately dependant on observations made at mid-latitudes and therefore only really representative of the effects of eruptions on mid-latitude climate. The Volcanic Explosivity Index (VEI) is a system that ranks eruptions using only volcanological criteria to assess the magnitude, intensity, dispersion and destructiveness of a volcanic event. It does not rely on temperature and solar radiation measurements at the surface so it can be useful for worldwide eruptions. These eruptions are ranked from 1 to 8 with 8 being the most explosive. Those eruptions presumed to have injected material into the stratosphere have a VEI of 4 or greater.

Past Effects of Volcanic Eruptions

Toba Bottleneck

Approximately 71,000 years ago a horrific volcanic winter was brought on by the eruption of Mount Toba in Sumatra. This volcanic winter followed by the coldest 1,000 years of the Last Ice Age caused massive death and famine to modern human and animal populations throughout the world. The results of the super-eruption of Toba may have also been a "bottleneck" in the evolution of modern humans. A "bottleneck" is an abrupt decrease in population, followed by rapid "differentiation" - or genetic divergence - of the surviving populations. Anthropologist Stanley Ambrose of the University of Illinois proposes that a volcanic winter reduced human populations to "levels low enough for evolutionary changes, which occur much faster in small populations, to produce rapid population differentiation," Ambrose said. If, as he believes,the eruption of Mount Toba in Sumatra caused the bottleneck, "then modern human races may have diverged abruptly, only 70,000 years ago," Ambrose wrote in the June issue of the Journal of Human Evolution.

Laki Fissure Eruption

In 1783 there was a prolonged fissure eruption at Laki, Iceland that lasted for about 8 months. During this period 14 km^3 of basaltic lava was erupted and more than 100 million tons of sulfur dioxide (SO2) was sent into the atmosphere. The results were catastrophic on Iceland: 75% of the livestock died and there was an all-out crop failure. The resulting famine claimed the lives of about 25% of the Icelandic population. In both Europe and North America cold records were broken. The cooling effect of the Laki eruption in the northern hemisphere is estimated at 1 °C.

Tambora Plinian Eruption

In 1815, Tambora which is located in Sumbawa, Indonesia, exploded with a violence unparalleled in recent history. It was a plinian eruption that produced more than 50 km^3 of magma and emitted about 200 million tons of sulfuric acid aerosol into the stratosphere. It may have been one of the main causes of "the year without a summer" in 1816. The average decrease in temperature in the northern hemisphere is estimated at 0.4 - 0.7 °C.

Sources:

Volcanic Air Pollution-A Hazard in Hawaii

Volcanic Gases and Their Effects

Ancient Volcanic Winter

Climate Change: A Brief Review

Volcanoes and Climate Change

Image taken from Ministry of Agriculture and Forestry, New Zealand

http://www.DOMAIN/PATHNAME.HTM -- Revised: 20-December-2000
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