Some pictures of volcanic eruptions are iconic – this is one such example.
On 12 June 2009, Sarychev Peak erupted explosively. During the eruption, the International Space Station luckily passed overhead and the astronauts on board took this spectacular image of what appears to be a eruption column punching through the clouds.
Sarychev Peak is one of the most active volcanoes of the Kuril Islands, a volcanic archipelago about 1,300 km NE from Japan. Eruptions at this volcano have been recorded since the 1760s and include both quiet lava effusion episodes and violent explosions.
This photograph is more than a pretty picture. It is pretty exciting as it captures several volcanological processes that occur during the explosive volcanic eruptions.
On first glance, what you see is an eruption column rising from the volcano into the atmosphere. This plume also appears to be capped by white clouds or steam. Looking down at the island, you can also see ground hugging as clouds around the volcanic flanks.
The main eruption column: volcanic plumes are a mixture of hot volcanic ash, gases and entrained atmospheric air. Plumes steadily rise until the density of the plume matches that of the atmosphere, at which point the cloud often extends laterally.
The plume here is a dark grey colour, however, it progressively pales with increasing height. This is due to the concentration of ash in the plume. High quantities of ash in the cloud results in a dark grey appearance and so with decreasing quantities of ash, the paler the cloud gets. Consequently, the reduced concentration of ash reduces the cloud’s density meaning that it can rise higher in the atmosphere. So here in the photo of Sarychev, we can see the less dense, pale grey portion of the plume reaching the highest heights above the volcano.
The white cloud: According to the NASA website, “the smooth white cloud on top may be water condensation that resulted from rapid rising and cooling of the air mass above the ash column. This cloud, which meteorologists call a pileus cloud, is probably a transient feature”.
Pyroclastic flows: Looking at the volcanic island, emanating from the volcano is a cloud of dense, dark grey ash hugging the ground. This is probably a pyroclastic flow. There is another pyroclastic flow in the photo, a light grey in colour heading out to the bottom right of the image. Pyroclastic flows are ‘collapsed eruption columns’ causes it to hug the ground, descending from the volcano summit at speeds of hundreds of kilometers per hour.