Volcanic Ash and Winter Rain Can Make a Dangerous Mix

The heavy blanket of volcanic ash spread over the Andean landscape of southern Chile and Argentina will present new hazards during the coming weeks.

Even with the Puyehue-Cordon Caulle eruption ongoing, inches and even locally feet of ash have already settled over the rugged border region, where the Southern winter normally brings heavy precipitation, both as rain and as snow.

Eruption cloud streams from Chilean volcano into southern Argentina as fresh ashfall covers a wide area.(NASA image taken June 13, 2011)

The danger, according to Chile's Service of Minerals and Mining (SERNAGEOMIN), is that heavy rainfall could wash enormous volumes of ash off slopes, thereby choking streams and causing them to rise out of their banks. Such flows of wet volcanic ash are known as lahars.

Forecasters at AccuWeather.com expect moderate to heavy precipitation, both as rain and higher snow, in the ashfall area through the end of the week.