Wednesday, January 25, 2012

The Mechanics of the El Hierro Eruption (and current update)

The El Hierro volcano is a vexing one to watch and attempt to predict. While predicting any volcanic activity is not a science, more of an art, there are some typical signs for volcanic eruption that most scientists use to gauge the intensity, duration, and potential eruption time window. For El Hierro it seems, a lot of these rules are out the window and useless.

Harmonic Tremor (HT) is a seismic signal that is typically generated after preceding earthquakes, which indicates moving magma underground. This is usually indicative of an ongoing or soon to be starting eruption. This is not always so however, as El Hierro has proven time and again during this eruption. Some days, there are many smoking lava balloons and an intense jacuzzi, despite an absence of HT or earthquake activity. Slow effusion of underwater lava it seems can be independent of any HT signal. This has been the case now for weeks.

To scientists and remote bloggers, using HT monitors could give the false impression that the eruption has ended (Jon Frimann of the Iceland Volcano Blog uses this reasoning a lot). Without visual confirmation of the cone underwater, some bloggers leap to the conclusion that with an absence of strong HT, that the eruption MUST be over. If you were looking at an erupting cone, but your seismographs weren't showing any tremor, would you believe your eyes, or your instruments?

There are of course many other indications of an ongoing eruption. Gases, CO2 and SO2, can tell scientists what is going on inside the magma chamber. SO2 is usually indicative of a stable, and mild eruption, while large spikes in CO2 usually precede larger explosive activity. Monitoring these gases in real-time is the best way to really gauge the 'attitude' of the volcano at any given moment. CO2 and SO2 emissions at El Hierro remain stable, which suggests a stable eruptive cycle for now. If there are any spikes or dips, this could merely mean the magma chamber is either gearing up for a large explosion, or simply recharging/reloading.

Despite the fluctuations in HT and SO2/CO2 emissions, the visual observations of El Hierro don't seem to match up with instrument data very often. This is a unique volcano, like all of the other volcanoes of the world, and each has its own mechanisms for erupting, so using old methods from more active volcanoes simply will not produce the same results. Its important for those that monitor this volcano to realize that the eruption will only be "over" when the volcano is out of juice. Given the long duration of this eruption, and the supposed size of the magma chamber, I don't see this eruption ending any time soon. It will likely go on for a few more months, if not a year.

We do not know the exact size of the magma chamber, but like the Hawaiian Islands, Iceland, and other "hotspot" type volcanoes, eruptions can last years, or simply have a tiny eruption. The eruption at El Hierro is very much like the eruptions of Hawaii, specifically those of the Loihi Seamount, where an underwater volcano (that last erupted in 1996) is expected to one day create a new Hawaiian Island (in about 10,000 years or so!). The eruption at El Hierro is much shallower than Loihi so the time table here is around a couple of months if it keeps going. There has been an ongoing eruption in Hawaii from Kilauea since 1983, proving that sustained eruptions can and do occur on hotspots. This could be the beginning of a long term eruption at El Hierro... I would not be surprised.

This morning El Hierro is displaying vigorous jacuzzi activity, with occasional bursts of smoking lava stones. HT is gradually picking up again (which only means that somewhere in the chamber, magma is moving), and a few quakes were recorded. The activity has consistently ramped up on the surface the closer the vent gets to the surface of the ocean, and I expect it will continue to do so.

No comments:

Post a Comment

Comments are moderated. See the comment policy for details.