AFTER WHAT HAS been a quiet 2015, Etna saw one of its first paroxysms of the year. Over the last few weeks, the Voragina crater on Etna has been restless, with low level Strombolian activity that was mainly confined to the crater. However, last night, the Voragine crater unleashed a lava fountainthat reached 1 kilometer (~3,200 feet) over the volcano with an accompanying ash plume that topped 3 kilometers (~9,800 feet). Even with all that intensity of eruption, the paroxysm was over in only 50 minutes.
This was Etna’s first significant eruption since May 2015, when the activity was centered at the New Southeast Crater, but the Voragine Crater had been sputtering lava occasionally since the start of the year.
This past Saturday there was an unexpected eruption of Japan’s Ontake volcano. Below is a video of some first hand footage of the eruption. As usual, Erik Klemetti writing for Eruptions blog at Wired.com has the 411 on the eruption and why no one saw it coming.
Based on what I’ve read and seen (and this is speculation on my part), this eruption may have been a steam-driven explosion known as a “phreatic” eruption. The Japanese Meteorological Agency suggested that even compared to a smaller eruption in 2007, this explosion had almost no warning. This occurs when water seeps into the cracks in the crater area of a volcano and gets hot enough to flash to steam. This rapid boiling causes fracturing of the rock and explosively ejects material out of the crater as the pressure inside the crater or conduit goes up exponentially.
Klemetti reminds readers that there is no way to predict most volcanic eruptions, and thus not to blame volcanologists or the hikers for being there. Below are Klemetti’s tips for hikers who are planning a volcano hike, more detail at Eruptions blog:
How do you prepare yourself if you’re hiking in volcanic terranes? Here are a few tips:
Get to know your volcano.
Be doubly prepared.
Let people know where you are.
Understand the risk.
Mount Ontake, a volcano straddling Nagano and Gifu prefectures, erupted around 11:53 a.m. Saturday, leaving several hikers injured and stranded in mountain trails.