CONVULSIVE MELTWATER OUTBURSTS IN THE UPPER WABASH VALLEY OF NORTHEASTERN INDIANA: IMPLICATIONS FOR ICE SHEET COLLAPSE, MODERN BIOLOGICAL DIVERSITY, AND GEO-TOURISM

The upper Wabash Valley of northern Indiana and some of its tributaries were repeatedly scoured by enormous, landscape-altering outbursts of meltwater during deglaciation, carving what some early geologists likened to a “miniature scabland” into the exhumed carbonate bedrock. At least three major glacial floods from different parts of the decaying Laurentide ice sheet sculpted the valley in Wabash and Miami Counties. The spatial and temporal relations of the outbursts imply 1) abrupt, nonsynchronous collapse of geographically distinct parts of the ice sheet, associated with 2) the release of massive volumes of meltwater stored in and beneath different parts of the glacier. This style of deglaciation provides a genetic explanation for the abundant lake sediment that makes up most of the clayey Erie Lobe “till” that caps the regional glacial sequence.

The convulsive drainage history is directly responsible for one of the most iconic landscapes in Indiana, whose dramatic and unexpected geologic scenery contrasts sharply with the rest of northern Indiana. This reach is renowned for its exposures of Silurian pinnacle reefs, and features deep gorges, hanging valleys, numerous waterfalls, exhumed bedrock valleys and paleokarst, and a variety of superposed drainages of different ages, origins, and elevations—all indicative of a disequilibrium landscape that continues to be affected by a torrid pace of stream incision as it adjusts to events that occurred more than 14,000 BP. The remarkable geomorphic diversity of the region forms the backdrop for some of Indiana’s most storied cultural history, and for one of the most biologically diverse landscapes in the state: a single, 56-ha natural area, for example, hosts over 500 plant species—more than a quarter of the entire number known in the state—along with regionally unique animals, reptiles, and natural communities.

The concentration of diverse, geologically-driven micro-environments and significant historical sites found in the upper Wabash Valley is not replicated elsewhere in northern Indiana, prompting ongoing conservation efforts that have resulted in a nearly contiguous corridor of protected geologic features, historical localities, new nature preserves, and interpretive sites that showcase stellar examples of Indiana’s natural heritage.