Jr. Goff et al., RECENT HOLOCENE CHANGES IN SEDIMENTATION IN A LANDSLIDE-DAMMED LAKE IN THE CASCADE-MOUNTAINS, SOUTHWESTERN BRITISH-COLUMBIA, CANADA, Holocene, 6(1), 1996, pp. 75-81
Landslide-damming of Silver Lake in the Cascade Mountains took place a
bout 1000BP, Delta growth favoured the faulted west valley side. At th
e commencement of logging activity in AD 1946 the course of Silverhope
Creek was diverted away from access roads. As a consequence, the chan
nel shifted from the west to the east side of the valley, forming a ne
w delta. Six gravity lake cores and SCUBA surveys of lake sediments re
veal changes in the depositional regime. In two cores, late Pleistocen
e-early Holocene sediments are preserved. Old delta abandonment, new d
elta growth, reorientation of turbidity channels and confluence zones
are discussed. Cs-137 data show that, Following channel diversion, lit
tle or no further deposition occurred on the old delta. Assuming that
the 1964 Cs-137 maximum has been recorded in each curt, sedimentation
rates apparently decrease to the NNW, away from the new delta, and Cs-
137 values increase northwards. Stratigraphy, C-14 and Cs-137 dates in
dicate that there has been a recent increase in sedimentation rate of
about 20 rimes near the deltas, to about 10 times in a mid-lake locati
on. Erosion and the release of destabilized glaciolacustrine valley-si
de sediments into the creek enhances sedimentation in Silver Lake. Uns
table sediments on steep valley sides prohibit forest regrowth.