Wednesday, November 2, 2011

Chile lowers alert level for Hudson Volcano (Cerro Hudson)

Chilean authorities today allowed the return of residents that were evacuated within 45km of Cerro Hudson which 'awoke' last week to put on a small show. While this volcano has, in the past, been subject to violent and highly destructive eruptions, it seems this new phase was characterized by super heated water making its way up to three vents within the caldera. Chilean scientists and USGS have determined that no magma movement was actually detected in this eruption.

When glacial melt water accumulates and seeps into a volcanoes hot center, it can pressurize and make its way back up to the surface. Sometimes this results in what is called a 'phreatic eruption', meaning an eruption of gas and steam. These eruptions are typically far less dangerous than a magma eruption, and typically don't last long. Think of it sort of like shaking a bottle of Coca Cola and then opening it. A big blast of gas and liquid comes out, but subsides quickly.

The eruption at Cerro Hudson did create small amounts of ashfall near the volcano (as seen below)and blackened the snow topped mountains in the vicinity with a thin layer of ash. This ash was likely ash from a previous eruption, and not newly formed ash, as no magma was involved. The steam picked up the ash that was already on the caldera floor, and carried it with the steam.


However, as with most of these Andes range volcanoes, we can certainly expect more in the coming months from Chile, as activity has been at a high level for a lot of their volcanoes. The eruption at Puyehue-Cordón Caulle is ongoing, as with Chaiten. Eruptions from Llaima volcano, and Villarrica are frequent and typically cause lots of headaches for nearby residents and neighboring Argentina.

For now, it seems that Chileans can breathe a sigh of relief that this time, Cerro Hudson was kind enough to spare them the same misery caused by the recent Chaiten eruption, which caused severe damage to a nearby town of the same name, and blanketed Argentina with ash. The Chaiten eruption proved to be the biggest eruption this decade in Chile and one of it's all-timers. The area is still considered unfit for human habitation, and the instability of its growing obsidian dome remains a concern.

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