Landscape Evolution Modeling (LEM) is used to understand how landscapes evolve over millions of years. It is based on a regular grid of cells, each representing a height in the landscape. For each simulated year, we follow the processes of computing: how water flows between cells, the summation of water flowing through cells and the amount of erosion/deposition. Traditionally, due to computational complexity, such simulation models have only been performed on trivially small landscapes of 5,000 cells taking 5 hours to compute 1,000 years. However, researchers wish to perform simulations on massive landscapes (50+ million) over millions of years. We demonstrate here PARALEM, a GPGPU-enabled LEM capable of two to three orders of magnitude speedup in comparison to the best-in-class LEM software.