Volcano that cooled Earth in 1831 identified, scientists say

Even though it was one of the largest volcanic events of the 19th century, the source of an 1831 eruption remained a mystery until just recently, according to a report last month. Researchers identified the Zavaritskii caldera in the Kuril Islands near Japan as the source of the eruption, according to the report published in the journal, Proceedings of the National Academy of Sciences of the United States of America.

How did this eruption cool the earth? The remote volcano’s explosion spewed sulfur dioxide into the stratosphere. Sulfur dioxide acts as a shield against solar radiation, the report explained. When the 1831 eruption occurred, the cloud of sulfur dioxide it sprayed into the stratosphere deflected enough sunlight to cool the planet by 1 degree Celsius—or roughly 1.8 degrees Fahrenheit.

How did researchers determine this was the source of the eruption? By examining the layers of tephra glass shards, sulfur and other elements in ice cores, researchers can determine the timing of volcanic eruptions, the report explained. The process works much like tree ring dating, according to the website RealClimate.org.

Researchers detected certain tephra layers embedded in polar ice cores taken from Greenland that registered the high-sulfuric 1831 event indicative of the volcanic eruption. Those tephra layers were later matched to the chemistry that would have been involved in an eruption of the Zavaritskii caldera at the same time, according to the report. That match, combined with other evidence, leads researchers to believe an eruption of the Zavaritskii caldera caused the cooling event.

Dig deeper: Listen to Paul Butler’s report on The World and Everything in It podcast about critical thinking and climate science.