DUELING EROSION FRONTS: GLACIAL BUZZCUTTING AND NONGLACIAL SCARP ENCROACHMENT LIMIT THE HEIGHT OF TROPICAL MOUNTAINS

Large-scale topographic analyses show that most mid-latitude mountain ranges have hypsometric maxima that lie between the modern and LGM ELAs. Such observations have given rise to the “glacial buzzsaw” hypothesis, which says that ice-driven erosion is effective enough to limit vertical orogen growth. Here we present evidence that glacial buzzcutting is also an important process in tropical mountain ranges, even though evidence of glaciation there is often limited to small, isolated patches. We hypothesize that climate variation in high tropical mountains leads to glacial and fluvial erosion taking turns driving landscape evolution.

Our work combines surface-exposure age dating of glacial landforms, field mapping, remote sensing, and topographic analysis to characterize the imprint of glacial erosion in the Talamanca Range of Costa Rica and the Central Range of Taiwan. ¹⁰Be dating of glacial landforms at Cerro Chirripó in Costa Rica confirms LGM timing of glacial erosion, and topographic analysis shows that LGM buzzcutting has occurred in both places. Fluvially driven escarpments currently propagate headward into extinct glacial valleys, and scarp encroachment into buzzcut landscapes appears to act quickly enough to erase most glaciated terrain during warm periods. We deduce that this oscillatory pattern of erosion has acted throughout the Pleistocene in these and other tropical ranges, often obscuring evidence of past glaciations. Ironically, the height of many of these hot, humid landscapes has been limited by erosion during cold phases.