We study how rocks change as they move toward the surface with 13 boreholes in the Melamchi Valley of central Nepal. We found that chemical weathering—the process that breaks down minerals like plagioclase—occurs deep underground in the south, but becomes shallower farther north and at higher elevations, owing to the influence of mountain building processes and monsoon climate. Fractures in the rock also play a key role by letting in water and air, which speed up weathering.

By combining lab analyses with borehole and geophysical data, we are building a 3D picture of what lies beneath the surface. This helps us understand how weathering works in active mountains, and why some areas are more prone to landslides or better at storing water than others.