 |
| 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. |
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.
3 comments:
There's something about the massive scale of these events that make them even more interesting. I look forward to reading any subsequent studies on the potential mechanisms behind the proposed rapid groundwater recharge.
I have only read the abstract to the paper, so I don't know their full argument. But, I do have a question about the source of the groundwater. Since the terminus of the ice sheet was across the northern extent of the flood basalt province, wouldn't a more obvious source be melt water from the outflow there? I find it hard to envision a mechanism to recharge the aquifers in a brief flood surge.
This is a great question! Rather than trying to answer it myself, I'm calling the attention of this question to the authors of the paper and asking them both to make sure that I wrote up the summary correctly, and to answer your question. I'm sure that they can do a better job than I can, and the dialogue may be interesting and fruitful. Thank you for your interest!
Post a Comment