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Volcano Watch — Volcanic eruptions temporarily reduce the effects of global warming

November 10, 2005

We are familiar with the effects that volcanoes have on our atmosphere and climate. Previous Volcano Watch articles have discussed how emissions of large amounts of sulphur dioxide gas from erupting volcanoes are injected high into the atmosphere to form aerosol particles. These reflect sunlight, causing global temperatures to drop for several years or more after a large volcanic eruption.

But new research, published this week, suggests that volcanic eruptions might have a more important role in climate modification than previously suspected. Volcanic eruptions might be keeping sea level rise, caused by global warming, in check.

Over the past 100 years, sea levels have been generally rising and this has been linked to the increased emissions of carbon dioxide into the atmosphere from industrial activity. Carbon dioxide is a Greenhouse gas which effectively traps heat in the Earth's atmosphere. This heat melts sea ice and glaciers, causing sea level to rise.

Researchers investigating the sea level record, however, observed that this rise has not been steady. Using computer models and observations, they tracked sea level variations and temperatures in the upper 300 m (1000 ft) of the ocean recorded during and following major volcanic eruptions in the late 20th century.

Decreases in the rate of sea level rise were observed 1-2 years immediately following major volcanic eruptions. After this period of time, sea levels rose rapidly once more as the volcanic effects wore off. Sea level has raised an average of 1.8 mm (0.07 in.) per year since 1950, a period that included several major eruptions.

The eruption of Mount Pinatubo is a particularly good example. When Mount Pinatubo erupted in 1991, the tremendous amount of fine ash erupted into the atmosphere was sufficient to reflect short-wave solar radiation and cool ocean surface waters. The cooling, of around 0.5°C, was enough to cause a significant change in the balance between liquid water and ice in the oceans, which caused an estimated drop in sea level of 5 mm (0.2 in.). But between 1993 and 2000 (a period when there were no large volcanic eruptions), sea level rose by 3.2 mm (0.13 in.) each year.

There are around 1500 active volcanoes around the world and at any one time, 10-20 volcanoes are usually in eruption. Most of the eruptions, however, are small in scale. Pinatubo's eruption in 1991 was of a size that occurs every ten years on average, making it a frequent occurrence in geological terms. The effect of these kind of eruptions on sea level are therefore of great significance.

Despite the clear effect of volcanic eruptions on world climate however, they are still not powerful enough to offset the effect of global warming caused by human burning of fossil fuels - which many scientists consider the primary cause of sea level rise. It has been estimated that over the last 110 years, the eruption of Mt. Pinatubo along with Indonesia's Mt. Agung in 1963 and Mexico's El Chichon in 1982 have reduced sea level rise by about 7 mm (0.28 in.) - only a fraction compared with the overall 180-millimeter (7.1 in.) increase in sea levels in the 20th century.

Volcanic eruptions can therefore only temporarily delay the effects of sea level rise caused by global warming - they cannot halt the process or change the long-term rate of change. But this new research is clearly an important step forward in our understanding of how our planet works and the role volcanoes play in shaping our climate.

Volcano Activity Update

During the past week, the count of earthquakes located beneath Kīlauea remains at low levels. Inflation continues, but has slowed over the past few weeks.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Part of the south crater rim slumped into the crater on November 7. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean, with a few surface flows breaking out of the tube. In the past week, flows were active on the steep slope of Pulama pali and visible at night (weather permitting) from the end of Chain of Craters Road.

As of November 10, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. Small bench collapses continue to occur at the ocean entry. Large cracks cross both the old and new parts of the bench. Access to the ocean entry and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There were no felt earthquakes reported on Hawai`i Island within the past week.

Mauna Loa is not erupting. During the past week, the count of earthquakes located beneath the volcano remains at low levels. Inflation has resumed after having slowed over much of the previous month.