Fascinating blogpost, with references, on a model of metamorphic rock exhumation in the Himalayas. Salient points:
1) Enhanced erosion caused exhumation that brought crystalline rocks to the surface.
2) If it happened, it was recent: “...evidence is emerging that is largely consistent with the hypothesis that southward extrusion during the Early to Mid-Miocene was facilitated by channel ﬂow”, so it has happened, if only for a while 20-15 million years ago."
3) It's not happening now: "There is much less evidence that channel flow in the Himalayas has been happening since. Current day zones of high exhumation and high rainfall are found further south where they are associated with brittle thrusting in lower grade rocks. This can be explained by viscous wedge models rather than by channel flow."
Another interesting area of potential modelling for flood geologists.