Extrusive volcanoes are not found in which one of the following mountains?

The correct answer is D, Himalayas. The Himalayas were formed by the collision of two continental plates, the Indian and the Eurasian, and such a collision does not produce volcanoes.

Volcanoes form mostly where an oceanic plate sinks beneath another plate, the subduction zone, so that the descending slab melts and magma rises to the surface. When two continental plates meet, neither sinks deep enough to melt in this way; the crust instead crumples and thickens into fold mountains. That is why the Himalayas have no active extrusive volcanoes, while the Pacific Ring of Fire, which rings the Pacific with subduction zones, is lined with them.

A is wrong because Alaska, on the northern Ring of Fire, has the volcanoes of the Aleutian arc and the Alaska Range. B is wrong because the Rocky Mountains region of western North America has volcanic fields and the Yellowstone hotspot. C is wrong because the Andes, built by the subduction of the Nazca plate, carry many active volcanoes such as Cotopaxi.

Exam tip: ocean-continent collision gives Andes-type volcanoes; continent-continent collision gives the Himalayas without volcanoes.