Volcanoes are mostly situated at the boundaries of tectonic plates, such as destructive plate margins where oceanic crust is forced beneath continental crust, or at constructive plate margins where new oceanic crust is being created. The Pacific Ocean is bordered by destructive plate margins, and so many volcanoes occur around its rim. This so-called ‘Ring of Fire’ runs through the Andes, across the Pacific to New Zealand, through Japan and the Kamchatka Peninsula of Russia, back across the Pacific to the Aleutian Islands and mainland Alaska, and down through the Western Cordillera to Mexico and the Andes. In contrast, the Atlantic Ocean only has volcanoes in a series of islands along the Mid-Atlantic Ridge.

The association of glaciers with these volcanoes is linked to either high altitudes, as in the tropical Andes, or to high latitudes as in Iceland, Jan Mayen or Antarctica. Glaciers on high mountains are generally thin, but an eruption can have devastating consequences because the combination of melting ice and loose debris can generate unpredictable fast-flowing mudflows called lahars. Where the ice is several hundred metres thick, as in Iceland, large volumes of meltwater are generated during subglacial eruptions. In Antarctica, geologists have documented subglacial eruptions in the rock record, but these eruptions have had little obvious impact on human civilization. Subglacial eruptions on Mars have even been postulated, here scientists have inferred that ice sheets once were much more extensive than the small ice caps of today.