Volcanoes and weather

Volcanoes have the ability to send vast amounts of chemicals, in the form of gases and particles, into the earth’s atmosphere, sometimes with resulting impacts on weather patterns.

A general pattern of the distribution of volcanoes can be observed on the earth around the Pacific Rim region known as the Pacific Ring of Fire and in other “hot spots” associated with active and past tectonic margin zones. The significance of volcanic eruptions for weather is both direct and indirect. Water vapor plays an important role in the formation of humidity in the air and the ability of the air to absorb and heat, at least at local levels. Dust particulates, extremely prevalent in these eruptions, can form condensation nuclei, the bases for the formation of precipitation. Additionally, as these aerosols spread into the upper atmosphere and around the world, they tend to diffuse incoming solar radiation, producing a general, well-documented cooling effect on weather.

Some scientists think that volcanoes contributed to the early formation of Earth’s atmosphere. Effluents from volcanoes and steam vents have probably always been similar in nature to those seen today: about 80 percent water vapor and 10 percent carbon dioxide, along with components of sulfur dioxide and various dust particulates.

In a paper he read before the Philosophical Society of Manchester England, on December 22, 1784, Benjamin Franklin put forth the idea that volcanoes play a role in modifying climate. Franklin reported that in the wake of the volcanic eruption of Laki crater in Iceland in 1783, he had observed a reduction in the intensity of sunlight. He suggested that a “dry fog” produced by the volcano was preventing sunlight from entering the lower atmosphere. This in turn, he suggested, was the contributing factor in producing a very severe winter in western Europe and the eastern United States during the 1783-1784 season. Franklin’s proposal was based on the idea that volcanic dust was the major factor contributing to the reflection of sunlight. Additionally, it was believed that this effect could be observed only during violent eruptions. With later technological advancements, scientists were able to sample the upper and found that volcanic dust plays less of a role than do volcanic emissions of sulfate particles, which have been shown to affect surface temperatures.

Volcanic Emissions

The aerosols emitted from volcanoes that could have influences on weather are very complex. Aerosols are not simply the dust of crushed rock; they are composed of various chemicals and also maintain various shapes and sizes. It is known that volcanoes are a source of sulfate aerosols. These are sulfur-based particles that have highly reflective surfaces that have the capability of scattering sunlight back into space. Additionally, they can act as condensation nuclei for the formation of clouds and affect the structure of clouds, adding to their reflectivity and their ability to block sunlight.

Sulfur, in particular, after about two months in the atmosphere, combines with water vapor to form a haze of sulfuric acid. Such a volcanic haze may blanket the stratosphere for many years. The effect of this haze on weather and climate is found in its ability to reflect and absorb energy from the sun as well as to absorb infrared energy emitted from Earth. The results of these processes are a general cooling of the lower atmosphere and a warming of the stratosphere.

It has been suggested that the second-largest contribution to chlorine in the atmosphere, next to its mixing into the air from the oceans, is volcanoes. During non-eruptive stages as well as during violent eruptions, volcanoes emit chlorine gas. Volcanoes also contribute to injecting this chlorine high into the stratosphere, where it has the potential to interact with natural ozone as well as to add more aerosols into the atmosphere. It has been found, however, that volcanic gases can be infused high into the stratosphere without violent eruptions. Initially, scientists believed that only the largest of the particles erupted from a volcano made it into the stratosphere.

Major Eruptions

During the twentieth century, several major eruptions contributed to the injection of massive amounts of volcanic gases and particulates into the atmosphere. It has been estimated that in April 1982, the eruption of the volcano El Chichón in Mexico injected about 8 tons of sulfur dioxide gas into the atmosphere to an altitude of 32 kilometers (20 miles). In contrast, in May 1980, Mount St. Helens in Washington State produced almost a ton of sulfur dioxide, but, unlike in the case of El Chichón, its eruption did not cause any noticeable cooling.

In June 1991, Mount Pinatubo in the Philippines erupted, the second-largest eruption in the century since the Mount Katmai Novarupta eruption in Alaska in 1912. Pinatubo sent nearly 20 million tons of sulfur dioxide into the atmosphere, producing a noticeable worldwide cooling of about 0.5 degree Celsius (0.9 degree Fahrenheit) by 1992. Most models suggest that temperatures can drop from 0.2 to 0.5 degree Celsius (0.36 to 0.9 degree Fahrenheit) after a major eruption.

In January 2022, the Hunga Tonga-Hunga Ha'apai eruption in the South Pacific Ocean was one of the largest in recorded history. The volcano is underwater, so the magma ejected was superheated. The enormous volcano propelled 50 million tons of water vapor into the atmosphere. The blast extended for 162 miles (260 kilometers), with a pillar of ash, gas, and steam that extended 12 miles (20 kilometers) into the air. Scientists believed that the volcano will have some long-lasting effects on the weather. The northern half of Australia may have colder and wetter winters up until about 2029. North America, on the other hand, may have warmer than usual winters while in Scandinavia, winters will be colder than usual.

Mount Ruang in Indonesia began erupting in April 2024. It spewed volcanic gases 65,000 feet into the air, which is about 25,000 feet higher than commercial airliners fly. Scientists believed that the volanoe's eruptions will have little effect on the weather, however.

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