Κυριακή, 11 Νοεμβρίου 2012

Vulcan’s Views 11: Volcanoes Seen From Space


for more http://www.wired.com/wiredscience/2012/11/vulcans-views-11-volcanoes-seen-from-space-for-november-9-2012/?pid=5344&viewall=true
This week flew by for various reasons, so I thought I'd at least try to end the week with a bang. I haven't run a Vulcan's View since the summer, so it seemed like it was time to take a look down on some of volcanoes from the eyes sitting in space. Some are volcanoes that are currently erupting, some haven't erupted in thousands of years, but they've all left their mark on the landscape. As always, if you want to keep up with all the activity each week, be sure to read the Smithsonian/USGS Global Volcanism Program's Weekly Volcanic Activity Report.

Here we go!
Kilimanjaro, Tanzania Part of the East African Rift system, not only is Kilimanjaro an active volcano, but it is also the host to many glaciers (which are rapidly vanishing). At the peak (both of them) of the mountain, you'll find a number of pit craters sitting within a larger caldera, along with some rift vents splaying off the main summit. Interestingly, it is unclear when the last eruption of Kilimanjaro was, however, the youthful look of the pit craters at the summit suggest that eruptions have occurred in the last few hundreds to thousands of years. Image: NASA Earth Observatory




Shasta, California

Much like Kilimanjaro (the tallest mountain in Africa), Shasta is a monster of a volcano. Unlike Kilimanjaro, Shasta is an subduction-related volcano rather than a rift volcano, but they are very similar otherwise. Shasta has a prominent parasitic cone - Shastina - that has grown on the side of the larger edifice - and even a satellite cone to the west in Black Butte (north is to the bottom of the NASA Earth Observatory image). Both of these cones erupted during the Holocene (last 10,000 years). However, the last significant eruption at Shasta was only 216 years ago, when the volcano produced a VEI 3 eruption with pyroclastic flows and lahars speading in the valley surrounding the volcano.

Image: NASA Earth Observatory




Valley of 10,000 Smokes, Alaska

This year was the 100th anniversary of the Katmai-Novarupta-Valley of 10,000 Smokes eruption in Alaska, probably the largest eruption of the 20th century. When you erupt ~30 cubic kilometers of ash and volcanic debris, it lingers in the environment, especially in locations without abundant vegetation. The ash can be easily remobilized by winds, as we see in November 2012 image of ash blowing out from Katmai over Kodiak Island (above), or by rain, as happens around places like Pinatubo to form lahars. So, even though the eruption may have been a century ago, the lingering hazards remain.

Image: NASA




Alaid, Russia

Although not well-known, Alaid in the Kurile Islands has produced some of the largest explosive eruptions in the western Pacific island arc (and that includes the impressive Sarychev Peak eruption). It has been fairly quiet since the late 1990s, but in the 20 years preceding the last eruption in 1996, it had multiple VEI 2 eruptions and a VEI 4 eruption in 1981 that released almost half a cubic kilometer of volcanic ash and debris (tephra). One of the recent GVP Weekly Volcanic Activity Report noted reports of steam emissions and a thermal anomaly noticed by satellite.

Image: NASA Earth Observatory




Kizimen, Russia

Another recent entry in the GVP Reports has been Kizimen, where fresh lava flows have been spotted on the flanks of the Kamchatka volcano. This image (above) show the mostly steam plume with minor ash that the volcano has been producing. The report also mentions some small block-and-ash flows being produced from these lava flow fronts, something common at volcanoes like Kizimen.

Image: NASA Earth Observatory




Bezymianny, Russia

Bezymianny, also in Kamchatka, is one of the more picturesque volcanoes on the planet, with the healing avalanche scarp - like a fast-forward of Washington's St. Helens. This NASA Earth Observatory image shows that scarp and the dome, with most volcanic debris being funneled to southeast.

Image: NASA Earth Observatory




Heard Island, Indian Ocean

In the Indian Ocean sits one of Australia's few active volcanoes (albeit not on the Australian continent): Heard Island. It has erupted numerous times over the last century, but its remote location means that we don't know much about these eruptions. We do know that it does have occasionally small lava lakes at the summit -- and very well may have one right now, according to satellite images and thermal signatures.

Image: NASA Earth Observatory




Toba, Indonesia

For quite some time, the theory that the Toba eruption ~74,000 years ago caused a "genetic bottleneck" in human populations has been floated. This theory, by no means, is accepted by all geologists and anthropologists, but we can agree on one thing: Toba was one of the largest eruptions that has occurred since humans left Africa, erupting over 2,500 cubic kilometers of volcanic material. Some recent research has shown that the acid signature of volcanic aerosols likely from Toba can be found in ice on both polar icecaps, supporting the global influence of the eruption. The above Landsat image of Toba shows the scale of the caldera - it is 100 kilometers from end to end on the long axis! How big is that? It would fit snugly between Columbus and Dayton here in Ohio.

Image: NASA / Wikipedia




Indonesian Arc

Another recent research study in Geophysical Research Letters used satellite data - namely inSAR (Interferometric Synthetic Aperture Radar) to measure how much volcanoes along the Indonesia arc are inflating or deflating. Not surprisingly in such an active arc, they found that many volcanoes were showing signs of inflation or deflation during 2006-09 -- six in total (out of 80 observed) -- and three ended up erupting during that period. Now, that seems significant, but (caution: small sample size) that is still only 50/50, so we're far from understanding how much/little inflation is needed to be sure a volcanic will erupt. However, it does show how important remote sensing can be for longterm monitoring of volcanoes in places that are difficult to monitor from the ground.

Image: Figure from Chaussard and Amelung (2012), GRL

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