Research published in 2011 finds evidence that massive volcanic eruptions caused massive coal combustion , supporting models for significant generation of greenhouse gases . Researchers have suggested that massive volcanic eruptions through coal beds in Siberia would generate significant greenhouse gases and cause a runaway greenhouse effect . Massive eruptions can also throw enough pyroclastic debris and other material into the atmosphere to partially block out the sun and cause a volcanic winter , as happened on a smaller scale in 1816 following the eruption of Mount Tambora , the so-called Year Without a Summer . Such an eruption might cause the immediate deaths of millions of people several hundred miles from the eruption , and perhaps billions of death worldwide , due to the failure of the monsoons , resulting in major crop failures causing starvation on a profound scale
Year Without a Summer
Year Without a Summer
Global catastrophic risk