Volcanoes and the evolution of Earth's climate

Definition

Volcanic activity has played a major geological and environmental role in the evolution of the Earth since the planet’s formation. As the proto-planetary Earth cooled and formed a solid crust, widespread volcanic activity dominated its surface. The Earth’s interior at this time retained a considerable amount of heat from accretion and the decay of short-lived radioactive isotopes. With interior temperatures well above the melting point of most Earth materials, high-density metals sank to the Earth’s center of gravity, while lower-density, silicate-rich materials were displaced toward the surface. It is believed that this process took place within the first 50 million years of Earth history, resulting in the present crust-mantle-core structure.

Little geological evidence remains of the period between the formation of a solid crust and the beginnings of plate tectonics. Scientists believe that during this 2-billion-year interval, massive volcanic structures gradually built up into continental masses. Plate tectonics, as it is known today, began about 2.5 billion years ago. It may have taken that long for the Earth’s upper mantle to become sufficiently hot and fluid to create convection cells that could fracture the crust and spread these huge sections apart from one another. It is along these plate boundaries where the majority of earthquakes and volcanic eruptions take place.

Volcanic eruptions have a significant impact on the environment. During such eruptions, huge amounts of gases and dust are expelled into the atmosphere. Water vapor accounts for over 90 percent of the total expelled gas, with the remainder being a mixture of carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen, and fluorine. These gases can become harmful to life. When sulfur dioxide reacts with water droplets in the atmosphere, it becomes acid rain, which is highly corrosive and particularly harmful to vegetation. The tremendous amount of ash thrown from volcanic eruptions can also mix with water to form dangerous mudslides, or it can release fluorine, poisoning the animals that graze upon ash-covered vegetation. On a global scale, volcanic ash has its greatest effect on the upper atmosphere, where it prevents transmitted sunlight from reaching the Earth’s surface and eventually causes a reduction in global temperatures.

Significance for Climate Change

Throughout Earth’s history, life has been closely associated with volcanic activity. One theory suggests that life on Earth may have had its origin in volcanic hot springs that were rich in organic compounds. Continuous volcanic eruptions also contributed to the water that would later become the oceans. With life flourishing in the oceans and later on land, volcanic activity became a major influencing factor on the continuing evolution and periodic mass extinctions of Earth’s biological inhabitants.

One reason for the occurrence of mass extinctions is a dramatic change in the Earth’s surface conditions. Most species live in what can be called a “habitable zone” based upon a suitable range in temperature, the availability of sufficient water, and the right amount of sunlight. When a particular species is exposed to conditions outside of this zone, it either adapts to the changing conditions or dies. As compared to life in the oceans, life on land seems to be more fragile and more susceptible to change. Recent theories for the cause of mass extinctions have concentrated on cosmic impacts or extensive volcanic activity. In each case, the apparent mechanism can be related to a blockage of sunlight by the huge amounts of dust and debris that an impact or volcano would eject into the upper atmosphere. The reduction of even a small amount of sunlight could disrupt the photosynthetic process and through it Earth’s food chain. A break in the food chain not only affects all the species that depend upon that link for their nourishment, but also all the species that depend on those species, and so on.

Violent volcanic eruptions have also played an important role over the course of human history from both a social and environmental perspective. Perhaps the most famous volcanic eruption in history occurred in 79 C.E., when Mount Vesuvius erupted and buried the Roman city of Pompeii under a thick blanket of ash and debris. As devastating as the Vesuvius eruption was, it was a relatively minor eruption when compared to the eruptions of Mount Tambora in 1815 and Krakatoa (Krakatau) in 1883. Each volcano produced enough ash and dust to affect global climatic conditions for several years after its eruption.

The Indonesian volcano Tambora was the most powerful volcanic eruption in recorded history. Its ash cloud lowered worldwide temperatures by 3° Celsius, particularly affecting the Northern Hemisphere. The following year, 1816, was known as “the year without summer.” The United States and Canada experienced killing summer frosts and predominantly cloudy and cool days. Worldwide, with a shorter growing season, many people faced starvation.

Scientific studies of more recent volcanic eruptions, such as those of Mount St. Helens (1980), El Chichon (1982), and Mount Pinatubo (1991), have confirmed how much of an effect a single volcanic eruption can have on global weather conditions. One can only imagine the devastating effects that another giant volcanic eruption, such as the one that created the Yellowstone Basin in Wyoming (48 kilometers in diameter), would have on the world.

Bibliography

"About Volcanoes." National Park Service, 19 Sept. 2024, www.nps.gov/subjects/volcanoes/about-volcanoes.htm. Accessed 13 Dec. 2024.

Blong, R. J. Volcanic Hazards: A Source Book on the Effects of Eruptions. Orlando, Fla.: Academic Press, 1984.

Lang, Kenneth R. The Cambridge Guide to the Solar System. New York: Cambridge University Press, 2003.

Marti, Joan, and Gerald J. Ernst, eds. Volcanoes and the Environment. New York: Cambridge University Press, 2005.