Geologic features of the Connecticut Valley, Massachusetts, as related to recent floods

This report gives the results of a geologic study of certain features that bear upon the recent flood behavior of rivers flowing in the Massachusetts part of the Connecticut Valley. It is in part an outline of the physiographic history of the Connecticut River, a 'history that is treated in progressively greater detail as it concerns events occurring from Mesozoic time to the present, and in part a discussion of erosional and depositional processes associated with the extraordinary floods of March 1936 and September 1938. The Connecticut River flows southward through Massachusetts in a broad lowland area of more than 400 square miles and is joined in this area by four large tributaries, the Deerfield and Westfield Rivers from the west and the Millers and Chicopee Rivers from the east. The lowland area, or :Connecticut Valley province, is flanked on the west by the Berkshire Hills, a, deeply incised uplifted plateau, and on the east by the central upland, or Worcester .County plateau, a lower upland marked by rolling topography. Most of the broad, relatively flat valley floor is underlain by Triassic sedimentary rocks. Rising above it, however, are the prominent Holyoke-Mount Tom and Deerfield Ranges, which consist in large part of dark-colored igneous rocks, also of Triassic age. There is evidence of several cycles of erosion in central western Massachusetts, the last two of which are of Tertiary age and appear to have reached nature and very youthful stages of topographic development, respectively. Immediately prior to the glacial epoch, therefore, the Connecticut River flowed in a fairly narrow, deep gorge, which it had incised in the rather flat 5ottom of the valley that it had formed at an earlier stage. A Pleistocene crustal subsidence probably of several hundred feet, for which there has been only partial compensation in postglacial time, was responsible for the present position of much of this gorge below sea level. That an estuary does not now occupy the gorge is due to a filling by glacial debris, ...