Unlike some of its perpetually active neighbors on the Kamchatka Peninsula, Raikoke Volcano on the Kurile Islands rarely erupts. The small, oval-shaped island most recently exploded in 1924 and in 1778.

The dormant period ended around 4:00 a.m. local time on June 22, 2019, when a vast plume of ash and volcanic gases shot up from its 700-meter-wide crater. Several satellites—as well as astronauts on the International Space Station—observed as a thick plume rose and then streamed east as it was pulled into the circulation of a storm in the North Pacific.

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On the morning of June 22, astronauts shot a photograph (above) of the volcanic plume rising in a narrow column and then spreading out in a part of the plume known as the umbrella region. That is the area where the density of the plume and the surrounding air equalize and the plume stops rising. The ring of clouds at the base of the column appears to be water vapor.

“What a spectacular image. It reminds me of the classic Sarychev Peak astronaut photograph of an eruption in the Kuriles from about ten years ago,” said Simon Carn, a volcanologist at Michigan Tech. “The ring of white puffy clouds at the base of the column might be a sign of ambient air being drawn into the column and the condensation of water vapor. Or it could be a rising plume from interaction between magma and seawater because Raikoke is a small island and flows likely entered the water.”

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The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired the image above on the morning of June 22. At the time, the most concentrated ash was on the western edge of the plume, above Raikoke. The third image, an oblique, composite view based on data from the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP, shows the plume a few hours later. After an initial surge of activity that included several distinct explosive pulses, activity subsided and strong winds spread the ash across the Pacific. By the next day, just a faint remnant of the ash remained visible to MODIS.

Since ash contains sharp fragments of rock and volcanic glass, it poses a serious hazard to aircraft. The Tokyo and Anchorage Volcanic Ash Advisory Centers have been tracking the plume closely and have issued several notes to aviators indicating that ash had reached an altitude of 13 kilometers (8 miles). Meanwhile, data from the CALIPSO satellite indicate that parts of the plume may have reached 17 kilometers (10 miles).

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In addition to tracking ash, satellite sensors can also track the movements of volcanic gases. In this case, Raikoke produced a concentrated plume of sulfur dioxide (SO2) that separated from the ash and swirled throughout the North Pacific as the plume interacted with the storm.

“Radiosonde data from the region indicate a tropopause altitude of about 11 kilometers, so altitudes of 13 to 17 kilometers suggest that the eruption cloud is mostly in the stratosphere,” said Carn. “The persistence of large SO2 amounts over the last two days also indicates stratospheric injection.”

Volcanologists watch closely for plumes that reach the stratosphere because they tend to stay aloft for longer than those that remain within the troposphere. That is why plumes that reaches the stratosphere typically have the greatest effects on aviation and climate.