Tuesday, January 3, 2012

Smoking Lava Stones at El Hierro This Morning

Video from El Hierro this morning showed smoking lava stones on the surface of the water intermittently, during a period of supposed low harmonic tremor. Many bloggers and volcanologists are under the assumption that a volcano only erupts when harmonic tremor is detected, leading them to falsely report this eruption is at its end. Again, El Hierro is still erupting. You don't get floating lava rocks freshly steaming at the surface from a volcano that is not erupting, period. Earthquake activity has also picked up again on the island.

Harmonic tremor does not denote an eruption. It precedes an eruption. There are a few stages to an eruption, the first is earthquake swarms from breaking rocks and underground explosions. Second, harmonic tremor starts when magma finds a channel toward the surface. Once a channel reaches the surface, you generally have an eruption with a decrease in harmonic tremor. Once the channel of lava becomes more stable, harmonic tremor decreases. If the vent collapses and plugs the main fissure, harmonic tremor will again pick up, building pressure and attempting to find another outlet. This is what is occurring at El Hierro. The summit vent has collapsed several times. When it does, you see harmonic tremor pick up.

The vent at El Hierro has collapsed several times, each time harmonic tremor drops, and people say "Oh the eruption must be over". Shortly after there is always an explosion, with lava rocks reaching the surface, with another gradual decrease in tremor (when the vent can erupt again). The likely scenario is that the vent has a stable magma tube coming to the surface, and periodically gets plugged, which results in collapses and underwater explosions. This is NOT simply hydrothermal, as magma/lava is rarely involved.

My own thoughts are that El Hierro will continue to be active for a long time, and will continue its on/off phases until it finally gives up the ghost and settles down. However the vastness of the underground low-velocity zone, coupled with CO2 emissions on the island itself suggest that this may not be the only vent that will open up during this eruption. As I've pointed out in an earlier post, there appears to be two separate magma chambers under El Hierro, a smaller one to the ENE of El Hierro, and one to the WSW/SE of El Hierro (covering the area of El Golfo to the E of La Restinga, and through the main island). I believe the smaller one is related to the erupting vent, and the bigger one may not have erupted yet (and may or may not).

It is still too early to say whether or not El Hierro is in its last gasps, even though some other bloggers seem to think so. I surely do not.

I will post more updates as they become available.

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