Small Explosive Eruptions at Cleveland in Alaska

An AVHRR satellite image of Cleveland volcano in Alaska, taken May 4, 2012. The bright dot in the lower middle of the image is the summit of Cleveland, showing elevated temperatures. The plume extends to the east-north-east (right) of the volcano. Image: Alaska Volcano Observatory / University of Alaska Fairbanks, Geophysical Institute Little bit of news coming out of Alaska this weekend: the Alaska Volcano Observatory raised the aviation alert status at Cleveland to Orange after a sequence of explosive eruptions were detected. At first, there has been no visual confirmation as seeing conditions didn't allow for direct observation, so how did we know there was an eruption (or several, in this case)? They were detected by infrasound -- that is, sounds made by a volcanoes that are very low frequency, typically less than 20 hertz. This is well below anything a person can hear and are generated by magma motion and explosions during an eruption. Infrasound detectors can "hear" these sounds from thousands of kilometers away due to the ability of infrasound to travel easily through water, land and air, so they can propagate around the globe. Infrasound has been used numerous times to detect both near and far eruptions from Fairbanks, Alaska, where a number of infrasound receivers are located. Although infrasound technology has been around for decades, only recently has it been brought in as a key piece of volcano monitoring, as it can detect explosions like what occurred at Cleveland when both visibility is poor and seismometer coverage isn't available. The second explosion detected by infrasound, at 7:17 AM (UTC) on May 4, was spotted by satellite (see above) -- a small plume reaching 4.5 km (15,000 feet) and elevated summit temperatures. This activity seems be have become more continuous, with the seismic station at Okmok, 120 kilometers away, recording some of the tremor. However, by Sunday, the tremors seem to have subsided to some degree, suggesting the eruption might be waning. As are common at Cleveland, this eruption might be a dome collapse followed by sub-plinian explosions caused by the rapid release of pressure on the underlying magma below the summit. Not much to see right now on the Cleveland webcam, but conditions look to be cloudy. One thing that did amuse me with the news regarding this new eruption at Cleveland was the ridiculously over-the-top article from the Christian Science Monitor, breathlessly titled "Cleveland Volcano explosions put air travel on alert: Who could be affected?" As I've mentioned before in this space, the reason why Aleutian volcanoes are closely monitoring is the trans-Pacific air routes over the islands, so volcanic ash clouds need to be monitored as to alert air traffic. However, the Christian Science Monitor might be getting a little too overexcited over a relatively minor eruption like we've been seeing at Cleveland for years ... heck, the first line of their article is "Is Cleveland Volcano the next Eyjafjallajökull?" Clearly, somebody needs to cut back on the espressos. On the other hand, the Daily Beast decided to call Cleveland a "dormant" volcano -- which it clearly isn't as it has been continuously erupting in the form of the small explosions and lava dome growth at the summit for the past few years. Would it kill you to crack open a textbook or at least visit the Global Volcanism Program to see the last time Cleveland erupted?