For volcanoes to emerge oceanic and continental tectonic plate has to collide. Oceanic plate will subduct (sink), and will melt. Molten plate rises through crusts and forms volcanoes.
In Himalayas two sections of continental crust and create mountains (they don't subduct and melt).
The Himalayas have few volcanoes because they were formed through the collision of the Indian and Eurasian plates, a process that does not involve subduction and therefore lacks the magma production necessary for volcanic activity. Instead, this collision leads primarily to mountain building. The rocks predominantly consist of metamorphic and sedimentary materials rather than volcanic materials.
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