A thick sequence (∼177 m) of aggradational deposits was studied in the lower Hope Valley. Valley fill is preserved in a tectonic depression, which is associated with a releasing bend on the active strike slip Hope Fault. Our results indicate that local basin subsidence since the last glacial maximum (LGM) occurred at a rate of 1.4–2.5 mm/yr, which roughly matches the regional tectonic uplift rate. The approximate balance between uplift and basin subsidence resulted in a local late Pleistocene sedimentary pattern that was primarily controlled by climate-induced processes of aggradation and degradation. Here we describe deposits and subsurface sedimentary structures from an exposure located near Glynn Wye on the southern side of the Hope Valley. Sediments at the base of the studied sequence comprise 55 m of lacustrine/deltaic deposits that are overlain by thick fluvial and glaciofluvial gravels. Infrared stimulated luminescence (IRSL) dating on the lake beds yielded an age of 60.3 ∼5.6 ka BP, suggesting late OIS 4 ( oxygen isotope stage ) age for the lake. A subsequent phase of fluvial aggradation buried paleolake deposits under 65 m of glaciofluvial outwash. This was followed by the progression of a glacial advance which deposited a moraine over the top of the sequence. A luminescence age (IRSL) of 32.1 ∼2.6 ka BP from the outwash deposit below the moraine indicates that glaciofluvial aggradation prior to the ice incursion was well advanced during late OIS 3. Postglacial fluvial degradation caused 160 m of incision into the lower Hope Valley, thereby partially excavating the deeper basin fill.

Abstract A study of the 68-mi (109-ktn) section of the Fraser Canyon between Lytton and Hope, British Columbia, along the Canadian National Railway (CNR) was made to determine what factors controlled slope stability on a regional scale. Engineering geology aspects concerning regional faulting and related minor structure, lithology, drainage and hydrology, geomorphology, climate, river geometry, and effects of man were considered. The most significant cause of slope instability was deflecting of the Fraser River into its bank by the presence of either an alluvial fail at a tributary mouth or a river bend. This deflection allowed extensive lateral erosion and resulted in severe oversteepening, which undermined the toe of the slope. Rockfalls, rock and debris slides, and washouts have been recorded for more than 20 years by the CNR. These data indicate that about 66% of all such incidents occurred opposite alluvial fans or on outside curves of the river. The average numbers of incidents per mile occurring opposite alluvial fans and on the outside of river bends are 5.6 and 3.3 times greater, respectively, than the average number of incidents recorded for river stretches without these characteristics. Regional faulting, climatic conditions, and effects of man were also found to be important causes of slope instability.