MOUNTAINS, GLACIERS AND BEARS, OH MY!: THE ST. ELIAS EROSION/TECTONICS PROJECT (STEEP) AND ITS LEGACY FOR ACTIVE TECTONICS AND TEAM SCIENCE

Southern Alaska provides a superb setting for evaluating competing influences of tectonic deformation and climate control on mountain-building: it hosts the highest coastal mountain range on Earth and boasts globally-high erosion rates onshore and deposition rates offshore. The St. Elias Erosion/tectonics Project (STEEP) integrated geophysical, geological, and geodynamic constraints to investigate the interplay between tectonics and climate in orogenesis. Under the unfailingly good-humored and dauntless leadership of Terry Pavlis, the STEEP team experienced weeks socked in at Bering Glacier camp, dozens of helicopter trips ranging all over the peaks of Chugach-St. Elias National Park, storms at sea, and multiple grizzly bear encounters in remote camps to unravel the story of mountain building in southern Alaska. Flat-slab subduction and collision of the Yakutat microplate, an oceanic plateau that increases in thickness from ~15 km beneath Bering Glacier to ~30 km to the southeast, drives rapid uplift of the St. Elias orogen. The thickest portion of the Yakutat plateau enters the orogen at the site of highest uplift and erosion over the last >5 Myr. Deformation and uplift of the St. Elias mountains shifted from north to south of the plate boundary, building the coastal topography that focuses the precipitation at the coast where active faults occur both onshore and offshore. Fault activity is modulated by glacial processes, with increased erosional activity coinciding with increased uplift rates onshore, and many offshore faults buried and rendered inactive by rapid glacial deposition. Glacial-interglacial cycles have led to pronounced fluctuations in erosion intensity, with glacial periods enhancing mechanical weathering, exhumation and sediment delivery to the continental margin. Beyond the major results from STEEP that elucidate the dynamic feedback mechanisms between tectonic uplift and climate-driven erosion, the project jump-started careers and collaborations going strong almost two decades later.