| Description: |
Duricrusts form near the top of or within the regolith. Once exhumed, they are resistant to erosion and are often observed capping hilltops. Two hypotheses have been proposed to explain their formation. One calls upon seasonal fluctuations in water table height causing cycles of dissolution and precipitation that concentrate hardening species transported from distant sources. The other assumes that hardening is the ultimate phase of laterisation of the regolith by progressive leaching of the soluble elements that leads to in situ concentration of the hardening species. Here we propose a numerical model for the formation of duricrusts following the latter hypothesis, which we will term the in situ or laterisation (LAT) model. In Fenske et al. ( 2025 ) , we developed a similar model representing the other model (named here the transport or Water Table Fluctuation (WTF) model). The LAT model we present here assumes that the rate of hardening is a self-limiting process that takes place at a rate determined by a laterisation time scale, τ l , and is linearly proportional to precipitation rate. Laterisation is accompanied by mass loss, at a rate set by a mass loss time scale, τ m , that can potentially be different from τ l and causes lowering of the topographic surface. We also test three laterisation modes, that depend on whether laterisation takes place above the water table only (percolation mode), below the water table (saturated mode) or everywhere (everywhere mode). This model for the formation of duricrusts is embedded in a previously published model for regolith formation ( Braun et al. , 2016 ) . Here we present results obtained from the new LAT model by varying both the model parameters and the external forcing functions, namely, U the uplift rate and P , the precipitation rate. We show that duricrust formation by laterisation is favored by a small uplift rate as well as a strong precipitation rate. The smaller the laterisation time scale and the mass loss time scale, the thicker the duricrust, but if the ... |