Santiaguito Lava Dome Complex
Posted by JAC on 4/27/2010, 6:43 am
 Santiaguito is a strange place. The first of the lava domes in the complex,  Caliente (the one erupting in the first photo, and the farthest to the right in the one above) began extruding from the 1902 eruption crater in Santa Maria in 1922. By 1929, the year that a 3 million cubic meter collapse and pyroclastic surge occurred, the dome had grown to about half a cubic kilometer in size. In the next 80 or so years, the other three domes - La Mitad, El Monje, and El Brujo - formed as the active vent migrated westward. Then, after a brief period when both Caliente and El Brujo were active, everything shifted back to Caliente. Currently, Caliente is looking more and more like a mini-stratovolcano - the old rubbly dome has long since been covered over by talus slopes and lava flows. At the summit, however, is a very strange situation. The main vent consists of two structures: an outer ring-shaped fracture set, and an "inner annulus", or smaller ring-shaped vent. During an eruption, jets of gas and ash are expelled from various points around these rings, and the both rings heat up. In addition, the eruptions are pushing out a blocky, viscous lava flow onto the SW slope of Caliente.  A Forward-Looking InfraRed (FLIR) view of the top of Caliente from the summit of Santa Maria. The outer ring is clearly visible as a bright, hot area, and there are radial fractures leading to the "inner annulus", which is somewhat harder to see. The pinkish patch on the opposite side of the dome summit is the lava flow, and there are several fumaroles below the summit on the near side. Temperatures are in Celsius, and brighter colors mean the surface is hotter.  A clip from a FLIR video of an eruption. The lava flow is clearly visible on the left side of the dome, and several jets are apparent in the eruption plume. These eruptions last for several minutes, and it's common to see the hot jets of ash and gas migrate around the ring fracture. Caliente's eruptions occur every few hours. That's right - not days, or weeks, or months - hours. It's amazing to watch, and even more incredible to listen to, because these eruptions sound exactly like a jet flying overhead. (Interestingly enough, people looking at infrasound - way below human hearing range - have found that volcanoes sound like jet engines there, too.) Occasionally these eruptions are large enough to produce pyroclastic flows, which eventually expand and drift and turn into a really annoying, view-blocking cloud around the base of the volcano.  This particular eruption, on the 15th of March, got reported in the local news the next day. The eruption plume, which came from both the vent and the pyroclastic flow on Caliente's SW slope, drifted to the SE, toward a number of small towns, rather than to the SW, which is where it usually goes and where there are mostly coffee plantations. It's not unusual to see ash coating coffee plants when you're driving through the fincas, although it seems that the nearby towns don't see it that often. Another interesting feature of eruptions is that they are often preceded and followed by rockfalls. These are really easy - and neat - to watch on infrared camera, and sometimes you can hear the cracking of house-sized blocks tumbling down the slopes. They're likely from the front of the lava flow, where oversteepened blocks are detached by the push of extrusion or just the shaking of the eruption itself. |
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In this thread:
Guatemala: explosive eruption at Santiaguito - JAC, 4/27/2010, 6:28 am
- Very cool close-up video of eruption at the crater (a little too close for comfort?) - JAC, 4/28/2010, 3:28 pm
- Volcano spews sand, ash over Guatemala - JAC, 4/27/2010, 6:34 am
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