IIRC, the Himalays are both the Asian and Indian plates crumbling. There're three types of plates touching: convergent, divergent, and transform (towards each other, apart from each other and alongside each other). There's two types of plates: continental and oceanic, of which the latter is much lighter .

The Indian plate and Asian plate are convergent and both continental. That means they generally just smash into each other, i.o.w. both crumbling. If one of them was oceanic, say Asia and the Pacific, the oceanic one would sink under the continental one, creating a valley or (Mariana) trench.