LACUSTRINE SEDIMENTATION IN NEW ENGLAND IMAGED WITH GROUND-PENETRATING RADAR: LITTLE EVIDENCE FOR CATASTROPHIC HOLOCENE LANDSCAPE ALTERATION

Evidence for inorganic sedimentary landscape alteration in New England is mostly hidden beneath vegetation. Evidence of landscape erosion processes are found within the sedimentation beneath small lakes, where low conductivity water often allows excellent subbottom signal penetration and imaging with ground-penetrating radar (GPR). These images, along with previous coring in many lakes, provide overwhelming evidence for lakewide, episodic, storm-driven turbidity currents and their effects upon sedimentation architecture beneath slopes, rises and basins. The lack of any lacustrine subbottom slumps, slides and faults indicates a Holocene history devoid of surrounding terrestrial spontaneous and catastrophic slope collapses or earthquakes. Horizon continuity and sediment depths validate core findings of sediment rates varying from 0.3 (Upper South Pond in central New Hampshire) to 0.6 mm/year (Ritterbush Pond in northern Vermont) to 1 mm/year (Mirror Lake in central New Hampshire). Thus the sedimentary architecture indicates relatively quiescent periods of fine grain hillside erosion, punctuated by severe storms occurring on average about every 200 years. The only Holocene exception found so far are apparent debris flows, evidenced by slight stratification and dense distributions of boulders, into Ritterbush Pond and which generated turbidity currents; glacial debris flows are evident in Mirror Lake.