Controls on rock weathering rates by reaction-induced hierarchical fracturing

Weathering of rocks takes place through complex processes involving an intimate coupling between mechanical disintegration of the rocks and interactions between the exposed rock surface, the hydrosphere and the biosphere. It is still poorly understood how this coupling affects weathering rates and patterns produced by weathering. Here, we show that the observed spheroidal weathering patterns in basaltic intrusions (dolerites) in the Karoo Basin in South Africa are created through volume expanding reactions which set up stresses that not only lead to spalling of spheroidal layers of rock, but also drive a large scale hierarchical fracturing process by which the dolerite is continuously undergoing domain division. The fracture processes generates new reactive surface area in a self-accelerating manner, thus providing a first-order control on the total weathering rate.