Sharp corners in materials can concentrate stresses and increase their chances of cracking (e.g., why airplanes have rounded windows). Likewise, the shape of Earth’s surface, from sharp ridges to gentle hills, can distribute stresses to fracture bedrock based on topography. Highly fractured bedrock may produce smaller boulders that fall into streams, whereas less fractured bedrock may produce larger boulders. However, bedrock may also be fractured by climate-based weathering, have preexisting fractures, or have layers that fracture differently than non-layered rocks. Here, we calculate stresses, map landslides, and measure boulders across different valleys on West Maui Volcano, Hawaiʻi, to test if stress, climate, or rock type are connected to landslide occurrence and stream sediment size. Our results suggest that rainfall-induced chemical weathering, layered lava bedrock, and volcanic rock weakening likely impact landslides and boulder size on West Maui Volcano more than stress. However, our data does not rule out the effect of stresses on bedrock fractures in ridges and the sediment they erode into streams. More studies on bedrock fracturing could improve our understanding of Hawaiian erosion and other cross-disciplinary studies, including stream ecosystems, flash flood hazards, and landslide preparedness.