Sarychev volcano (Russia’s Kuril Islands, northeast of Japan) - The plume has hit a layer of air with moisture in it. It’s raised by the plume causing a reduction in pressure (its now higher). That causes the moisture to form a cloud.
Heimaey Eruption: 1/23/1973 the town was awakened by a volcanic eruption. At first peo-ple thought it was a grass fire lit by children, but it turned out to be a large eruption. More than half of the town's houses were destroyed or severely damaged: some caught fire as molten lava rocks were scattered across the town, others collapsed under the ash. There had been no warning; everyone was caught completely by surprise