ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Quaternary hydrologic budget for the Mojave River system
requires quantitative estimates of discharge from the trunk
drainage as well as the contributions from local continental
interior watersheds. A mass-balance model, incorporating
the paleo-lake parameters and historic hydroclimatic data
for calibration, suggests that the Mojave River's discharge
during its overflow into the Sdv and Dv area increased due
to a 50 % augmentation in mean annual precipitation in
the near-coast Sbm and an accompanying decrease in average
temperature over the deserts. Although the Mojave
River's discharge during the early Holocene decreased sufficiently
to limit overflow from Lake Mojave into the Sdv
and Dv, intermittent pluvial lake conditions existed episodically
for the past 9,000 years.
A regional comparison of Holocene fluvial deposits indicates
that five periods of significantly increased precipitation
produced high-magnitude floods on the trunk river, created
fluvial terraces in headwater and canyon-constriction
areas, and formed shallow short-lived ephemeral lakes in
the terminal playas. Both l4C methods and age estimates
from playa sedimentation rates (0.28 m/ka from Sse
playas) document flooding of the Mojave River and pluvial
lake stands within the Ssc Lakes area between 0.2-0.7 ka,
3.5-3.9 ka, 5.0-6.0 ka, 7.0-7.5 ka, and 8.7-11.4 ka (latter =
waning stands of pluvial lakes). We infer that each Hypr
lasted form only a few decades up to a century in response
to increased frequency of winter storms across southern
California, resulting from shifts in winter atmospheric circulation
patterns over the North Pacific. Increased sheetflooding
across desert piedmonts surrounding the Sse and
DV playas occurred during one or more Hypr, implying
increases in the local desert precipitation as well as orographic
precipitation in the Sbm. However, enhanced precipitation
within the hyperarid parts of the Mojave River
drainage basin during the Holocene apparently did not
contribute significant runoff to these short-term pluvial
lakes. Measured and simulated peak discharges for historic
lake-producing flood events on the Mojave River, resulting
from this type of circulation pattern, range from 500 to
24,000 m 3/s. Such floods are capable of significantly altering
the channels of both fluvial systems by lateral avulsion
and/or incision, depending upon the local channel/valley
conditions. The most complete records of fluvial adjustments
to these Hypr appear to be in the headwaters of the
Sbm where coarse gravel aids in preserving the flood deposits.
The nature of these Holocene Hypr in the largest arid
fluvial system with differing hydroclimatic settings suggests
that short-duration climatic changes affected broad regions
of southern California.
W. BRIAN WHALLEyl, BRICE R. REAl
& FINLAY M. STUART 2
Exposure history of palaeosurfaces around the
margins of 0ksfjordj0kelen, North Norway,
as revealed by cosmogenic isotopes
1 School of Geosciences, Queen's University Belfast,
Belfast Bl7l nn, U.K.
2 Isotope Geosciences Unit, Surrc, East Kilbride,
Glasgow G75 OQF, U.K.
Nunatak/tors and blockfields in presently and past glaciated
regions have long been the subject of controversy regarding
their age, weathering origin and glacial history.
Around the margins of 0ksfjordj0kelen recently deglaciated
areas of bedrock and surficial deposits have been identified
and suggested as having potentially very different
ages and resulting from different formative processes. Some
bedrock regions are heavily striated with many quarried
lee-side rock faces indicating extensive subglacial erosion.
Other bedrock areas show evidence of possible subglacial
erosion but are extensively weathered. Finally, nunatak/tors
show no evidence of having undergone subglacial
erosion, but are extensively weathered by both chemical
and mechanical processes. Blockfields are found in
other areas around the margins and in places are greater
than I m deep. They are composed of a mixture of blocks
and fines and contain patterned ground and are found on
low-angled slopes sometimes in association with tors. Until
now, most of the dating research has focused on these saprolite
blockfields. The quantity and clay mineralogy of
the fines have led to the suggestion that they are palaeosurfaces
perhaps predating Pleistocene glaciations. The only
modifications occurring during the Pleistocene being frost
heaving with some mechanical and limited chemical
weathering with little or no glacial removal. The nunatak/
tors and the weathered, possibly subglacially eroded, bedrock
surfaces are composed of coarse, Caledonian gabbros
which are suitable for cosmogenic 3He-21Ne exposure
history studies. Results from these studies provide the
first exposure history data on these erosion surfaces. From
this we are able to tell relative age differences between the
surfaces thus allowing determination of the weathering environments
surfaces have been exposed to and thus the
processes which have formed them.
SUSAN WHITE
Karst of the Cainozoic limestones of the Otway Basin,
Southeastern Australia
School of Earth Sciences, La Trobe University, Bundoora,
Victoria 3083, Australia
The Tertiary and Quaternary limestones of the Otway Basin
in south western Victoria and south eastern South Australia
include Miocene and Oligocene marine limestones
and Pleistocene calcareous dune and beach facies. These
highly variable limestones of high primary porosity and high
permeability show diverse karst features both in surface
403