Monday, April 23, 2012

Island of Fogo Is Having Volcanic Tremor

The island of Fogo looks like something out of a sci fi fantasy movie. A massive island inlayed by a large caldera, with a spire-like volcanic cone in the center that looms high over the tropical landscape. Below the peak of Fogo (Pico do Fogo) lies a paved over, barren landscape, surprisingly home to houses and facilities built atop fresh lava flows. Fogo was one of the first volcanoes that fascinated me, given its striking appearance and remote location. To visit this volcano, for me, would be quite a sight.

Fogo is not a very well-known volcano, but it is capable of some serious eruptions. Indeed the original caldera forming event likely created tsunamis and landslides that would have hit the neighboring islands, and maybe even the African West Coast. The island itself is dotted with cinder cones young and old on its flanks, suggesting a very active life cycle as a volcano. Now, the volcano is getting seismic equipment installed on it, and already, results are coming in pointing to volcanic tremor, and small volcanic earthquakes. Fogo is waking up.  (or was it ever truly asleep?).

Fogo's last eruption occurred in 1995, when a small cinder cone was erupted on the WSW flank of the Fogo peak. This eruption started off as a fissure, and gradually built a cone, and produced slow moving pahoehoe lava flows that pooled at the base of the mountain.


Picture of the 1995 eruption of Fogo, from Smithsonian Global Volcanism Program website. Photo by Dick Moore, 1995 (U.S. Geological Survey)

The Smithsonian GVP Characterizes Fogo here:

"The massive 9-km-wide, horseshoe-shaped Cha caldera truncates the summit of Fogo stratovolcano, the most prominent in the Cape Verde islands. An ash plume (center) rises from the western flank of a steep-sided central cone, Pico, that rises more than 1 km above the caldera floor to form the 2829 m high point of the island. Pico, which is capped by a 500-m-wide, 150-m-deep summit crater, was apparently in almost continuous activity from the time of Portuguese settlement in 1500 AD until about 1760."

An eruption of Fogo today would likely be characterized by another small cinder cone building event, or possibly a larger more explosive event from the summit cone (which has not recently erupted historically speaking), which could be capable of strombolian type, or Hawaiian type eruptions. Flank eruptions on the West side of Fogo were considered to be Holocene, but most eruptions have occurred on the East side of the caldera rim recently. The West side of the island is heavily vegetated and is probably not at risk.

The Portuguese islands of the Cape Verde chain are all volcanoes, or have been volcanoes at one point in time or another (some are very old). Installation of more monitoring equipment is exciting news for some of us who long for a global volcanic monitoring network, and certainly for the scientists who will be poring over reams of seismic data. Every year, volcano monitoring gets better and better, and disasters and deaths are able to be more easily averted due to good early warning systems. It is my thought that within 10-20 years of today, we will actually be able to routinely scan a volcanoes magma reserves to determine whether an eruption is imminent, and when it might occur. The new muon-based mapping technology developed in Japan is a major step forward, and is currently being tested on volcanoes such as Vesuvius, and Fuji. 

If anything new develops on Fogo, you'll read about it here!

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