Wednesday, March 7, 2012

It Is Official: El Hierro Eruption Has Ended

INVOLCAN has declared the eruption of El Hierro to be over, and the alert status of the island has been lowered from Red to Yellow. The village of La Restinga can finally open its doors to tourists again, however maritime activity is still restricted due to probable degassing, and swimming in the water is still off limits pending a chemical analysis of the water to determine its safety. Sea life has already begun to repopulate the area, a good sign for the fisherman of the village.

The eruption at El Hierro was preceded by a lengthy period of volcanic earthquakes, which were used to size up the magma chamber. The island was on Yellow alert for a long time, before a "jacuzzi" was spotted in the ocean, and harmonic tremor increased. The eruption of the underwater cone "Bob" started as an underwater fissure eruption, eventually resulting in a cone building event. Several collapses of the main vent stalled the eruption, which stopped and started several times. On occasion, floating "Lava Balloons", or gaseous bubbles encased in molten rock, would float to the surface and emit steam, and sometimes flames once the bubbles burst and allowed oxygen to interact with the heat. This however was as exciting as the eruption got.

For about a month now, the eruption has all but ceased entirely. Harmonic tremor has been at low to background levels, and there has been very little if any surface activity since February. This is what led the scientists to declare the eruption over, although their maintaining of alert level Yellow does indeed reflect what many of us know, that activity can resume at any time, and caution is still in order. Some volcanoes have a small cone building event as a precursor to a larger eruption, something that is certainly not out of the question.

Current uplift sensors show the island to be stable, which could mean that the magma reservoir has not deflated, and merely extruded the lava to form "Bob" because it was the easiest path to the surface. Quakes are still ongoing at El Hierro in an area not near "Bob", and it is still worth keeping an eye on the island. El Hierro and the Canaries have been compared to the Hawaiian islands in regards to the type of eruptions it produces. The theory goes that El Hierro, like Hawaii, is a hotspot type volcano. These are highly unpredictable as we have no way of imaging or monitoring the mantle plumes that are though to be responsible for hotspot volcanoes.

It is my guess that activity will pause now for probably months, and either slow subsidence will take place, or activity will resume in another location. It is now a game of wait and see. In any case, I doubt that the residents of El Hierro will ever forget now that they are living on an active volcano, and will be ever mindful of the power that lies beneath their feet.

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