One of the most active volcanoes on Earth is Russia's Sheveluch. Over the past few decades, it has produced dozens of explosive eruptions while also building a new lava dome in the vacated remains of an even larger eruption and collapse. However, when it comes to volcano's like Sheveluch, all that work to create the dome can be ruined in a moment. A massive blast earlier in April looks to have eviscerated the Shiveluch's lava dome.
The dome (see above and below) had been growing off and on since 1980. Domes like this are created by the slow extrusion of sticky andesite lava. This viscous stuff doesn't flow particularly well, so instead a dome is built as eruptions continue. In the process, the dome can plug up the conduit that is letting lava and volcanic gases escape.
As you might guess, trapping volcanic gases and lava from easy escape might not be the best plan for such a dome. Occasionally, the dome gets too steep and will collapse and in doing so, it lowers the pressure the lava in the conduit feels. Lower pressure in lava means bubbles form and bubbles forming can mean boom! One of the most common forms of explosions at Sheveluch are triggered by dome collapse.
Some dome collapse explosions are relatively small, producing an ash plume that might reach a few thousand feet and dusting ash across the area. Occasionally, the explosions can be much bigger depending on the pressure building under the dome. In rare cases, the initial collapse can trigger such a big explosion that most of the dome is destroyed and ash is thrown tens of thousands of feet into the atmosphere.
That is what appears to have happened on April 10-11, 2023. Sheveluch unleashed one of its biggest explosion eruptions in years, with ash reaching 52,000 feet. Heavy ash fell on the towns around the volcano, with upwards of 6 centimetres (3 inches) of the stuff on top of the winter's snow. Towns over 30 miles away saw over 8 centimetres (4 inches) of ash fall.
This blast generated hot ash flows (pyroclastic flows) and nearly reached the major highway along the peninsula. In fact, some of the pyroclastic flows may have made it up to ~10 miles (20 kilometers) out from the volcano in a directed blast. Ash from the eruption causes flight cancellations and rerouting across the North Pacific and into western North America.
In photos taken after the eruption (see above), the damage to the dome is readily apparent. What was once a growing dome was reduced into a ~1 kilometer wide crater. The crater is still vigorously steaming and the lava dome has already begun to repair itself. This is the cycle of life at a volcano such as Sheveluch -- dome growth, dome destruction, dome growth (rinse and repeat).
In many ways, Sheveluch is like Mount St. Helens' hyperactive cousin. They have both experienced large collapses of part of the volcano leading to a massive eruption (1980 for Mount St. Helens and 1964 in the case of Sheveluch). They have also both seen new lava dome growth, but at the Washington volcano, that growth was much less explosion (and dangerous) than its Russian counterpart.
Why this difference might be could boil down to how much lava is being fed from below or how much gas in contained in that lava. In any case, the tale of these two volcanoes is shared at times and dramatically different at others.
