|Dry Falls, a 350 foot high, 3 mile wide group of cliffs|
that formed during the floods that scoured the
Channeled Scablands. Photo from the U.S. Geological Survey,
available here. Dry Falls is ten times the size of Niagara
Falls, and was formed over a short period of time during the
catastrophic Missoula Floods.
Tuesday, November 9, 2010
Where did the groundwater in the Pacific Northwest come from?
In a new paper, Brown et al. propose that these floods, in spite of their brevity, provided the groundwater that is now present within the aquifers of the Columbia River Basalts that cover the region (Brown, K.B., et al., Isotopically-depleted late Pleistocene groundwater in Columbia River Basalt aquifers: Evidence for recharge of glacial Lake Missoula floodwaters, Geophysical Research Letters, vol. 37, L21402, 5 pp, 2010.). This region is semi-arid today, and general climate models suggest that it was colder and drier during the Last Glacial Maximum. The groundwaters have anomalously low del O18 and delD values, and radiocarbon ages between 15.7 and 19.6 thousand years before present, and the authors suggest that they were recharged from multiple pulses of the Missoula flood events. Several groundwaters have even older radiocarbon ages and may have come from earlier undocumented Missoula flood events. The mechanism by which aquifers could be charged with such huge volumes of water in times of just a few days, even with repeated episodes, are unknown, but the large depth (366 m) and volume (>1200 cubic kilometers) of the ponds formed during the floods may have helped drive the water into the aquifers. These waters are important for agricultural and domestic water resources in central Washington, and--like the Great Lakes--may not be replenished under current geological conditions.