Indonesia is no stranger to volcano erup­tions. It currently has more than 150 volca­noes, 31 of them active with 8 erupting.

On February 1, as the last Newsletter was distributed, an Indonesian volcano erupted – Mt. Sinabung on the northern island of Sumatra. It had been spewing ash for months, but the sudden explosion at the beginning of the month killed 16 people, including a group of schoolchildren on a field trip to help distribute aid to the more than 30,000 people displaced by the volca­no’s activity. As tragic as the eruption was, it was a relatively small eruption, only 4 to 5 km high (2.5 – 3.1 miles high). It, like most Indonesian eruptions over the past century, was too small to affect climate.

On February 13, Mt. Kelud on the cen­tral Indonesian island of Java, exploded. Fortunately, the mountain had been rum­bling with seismic activity and the govern­ment warned 200,000 people to evacuate. More than 100,000 people fled to shelters and only four people died. Java closed its airports, as the mountain roared.

Then, as it historically does, Kelud qui­eted after a couple of days. Within three days, airplanes were flying and more than half the evacuees returned to take care of their abandoned livestock. There was even cheerful talk about the new jobs generated by the cleanup and the fertility that the vol­canic ash had added to the local soil.

The eruption was over, but the impact of Kelud’s eruption has only started. As the Browning Newsletter has repeatedly reported, a large volcano has a cascading effect on the climate. Most of the larger ash particles fall out within a few miles of the eruption. However, if the explosion is large enough to enter the quiet stratosphere, the volcanic aerosols (minute particles of ash and chemical debris) can linger for years. Water collects around these aerosols, form­ing micro-droplets too small to fall. These micro-droplets collect into thick clouds that continue to block incoming sun­light. This cools the surface of the Earth below. Eventually, the micro-droplets col­lect enough water and mass to precipitate out in the form of rain or snow. Since the clouds tend to be unusually dense – the precipitation frequently takes the form of blizzards or flooding rain.

However, the impact of large volcano eruptions varies, depending on the loca­tion of the explosion. Global winds tend to flow outward from the tropics toward the poles. As we saw following the 2011 erup­tions of Mt. Grimsvötn and Sheveluch, the Arctic or Antarctic air masses tend to trap debris from polar volcanoes. It affects the middle latitudes during the cold events of late fall, winter and early spring, but re­treats before summer warmth. The weather impact is concentrated, usually confined to one hemisphere.

Kelud will be different for several reasons.

David Fuller's view

There a number of important forecasts in this 8-page issue which may interest subscribers.