Toba or not Toba – that is the question

The study, led by researchers from the School of Earth and Environmental Sciences, and published in the journal Climate of the Past (Monday 18 October), provides new insights into the timing of the largest volcanic eruption humans ever experienced. These events are commonly referred to as super-eruptions and, by studying these extreme events, scientists can understand how climate and environment and human societies respond.

Volcanic eruptions can have huge impacts upon climate, both globally and locally. The eruption of Toba in Indonesia was the largest volcanic event of the last two million years and left behind a crater 100 km in diameter. There is much interest in determining the impact of such a huge event, particularly on the climate and human populations and the significance this had in shaping global climate and evolutionary development.

One of the main challenges with these ancient super-eruptions is that it is often difficult to pinpoint exactly when they occurred. To study past eruptions, researchers require a record of volcanic activity through time. One of the best records are ice cores. Sulfate deposited by eruptions can be preserved in ice for more than 100,000 years.

For the Toba eruption there are multiple sulfate peaks in Antarctic ice cores which may have resulted from the eruption, making it difficult to identify precisely when it occurred. To correctly determine when the eruption occurred, scientists measured the sulfur chemistry of each sulfate peak. This information encodes important information about the magnitude of the eruption and the height of the erupted plume, allowing the researchers to narrow down the most likely timescale for the Toba super-eruption.

This exciting new data allowed the research team to place the eruption in relation to the climate, including changes in precipitation and temperature. Using this analysis, the team suggests that the Toba eruption occurred on the transition into a cold period in the Northern Hemisphere almost 74,000 years ago. The relative timing suggests that the Toba super-eruption was not the trigger for the large Northern Hemisphere cooling at this time, but may have had an amplifying effect.

The paper New insights into the ~74 ka Toba eruption from sulfur isotopes of polar ice coresis published in the journal Climate of the Past [doi.org/10.5194/cp-17-2119-2021]