BEDROCK KNICKPOINTS AND TERRACES IN SOUTHERN NEW ENGLAND RIVERS

Bedrock knickpoints and fluvial terraces are ubiquitous features in the river and stream valleys of southern New England that attest to the legacy of glaciation and geomorphic processes associated with landscape evolution in the northern Appalachian region. These features are important for developing the proper long-term, Holocene landscape evolution context for considering the geomorphic processes that disrupt fluvial systems on continuous smaller, shorter time scales, such the role of beavers and woody debris, and more recently the historic land-use changes, mill pond sediments and modern dams associated with the influence of humans. Here, I present a preliminary analysis of a subset of terraces and bedrock knickpoints in southern New England. High alluvial fill and cut-fill terraces (up to 10-15 m above modern river levels) along the Connecticut River and its major tributaries dissecting the Berkshires and Western Connecticut Highlands (Deerfield, Westfield and Farmington Rivers), as well as along the Housatonic River and rivers within the Thames River Watershed, reflect incision into higher, glacial meltwater terraces. These terraces highlight the timing and style of post-glacial incision throughout the Holocene related to base-level controls on these river systems and post-glacial isostatic rebound. Bedrock knickpoints, meanwhile, are found along local stretches of bedrock rivers that commonly lie downstream of meandering, alluvial rivers or streams flowing through wetlands. Prominent examples include the Housatonic River at Bulls Bridge (CT), Deerfield River at Shelburne Falls (MA), Connecticut River at Turners Falls (MA), and Natchaug River at Diana’s Pool (CT). These knickpoints highlight the post-glacial reorganization of New England rivers throughout the Holocene as they occupy valleys scoured by glacial ice, incise into coarse glacial sediment and become superimposed on underlying bedrock. Less frequently, or perhaps in combination with this post-glacial reorganization, they speak to variations in rock strength or late Cenozoic incision of New England highlands in response to broader tectonic and climatic signals.