Damian Gosch, Kyle Brown, and Jennifer McIntosh Department of Hydrology and Water Resources University of Arizona Outburst Flooding of Proglacial Lake Waters: An Important Past Recharge Mechanism For Groundwater On Earth and Mars? Outburst Flooding of Proglacial Lake Waters: An Important Past Recharge Mechanism For Groundwater On Earth and Mars?

Location and extent of Columbia Plateau Basalts

Flood discharge pathways and glacio-fluvial deposits of Late Pleistocene Missoula Floods Catastrophic flooding from the breakup of ice-dammed Glacial Lake Missoula dramatically altered the landscape in the region, carving out the bedrock and depositing sediments; some of these features are evident today in the channeled scablands of central Washington (Baker and Bunker, 1985; Baker et al., 1991).

Regional climate since the Last Glacial Maximum During the Last Ice Age (~18,000 years ago) the Columbia Plateau region was just south of the Cordilleran Ice Sheet and the climate was cold and dry (4-8 o C cooler with 0 to 2 mm/day lower precipitation than the present). Outburst flooding from Glacial Lake Missoula may have provided recharge to basalt aquifers. Benito and Conner et al. (2003); Kutzbach, J.E. et al. (1993)

Oxygen and hydrogen isotopes as indicators of recharge source waters Shallow groundwater (< 100 m depth) in the basin have δ 18 O values within the range of modern precipitation. Deep groundwater ( m depth) have low δ 18 O values, indicating recharge under cooler climatic conditions.

Groundwater residence times determined using carbon-14 and oxygen isotopes Shallow groundwater (< 100 m depth) in the basin have ~100 percent modern carbon (pmc) indicating recent recharge. Deep groundwater ( m depth) have low radiocarbon values ( 10,000 years, within the range of the Last Glacial Maximum. Age calculation for carbon-14

Spatial distribution of paleoflood waters Sampled groundwater wells with carbon-14 values

Depth distribution of paleoflood waters

Columbia Basin- columnar basalts Mars-basalt columnar jointing Similarities between hydrogeologic setting of the Columbia Plateau and Mars

Baker et al. (1991) Martian hydrologic cycle

Evidence of outburst flooding on Mars Fairén and Baker, 2003

Baker et al. (1991) Evidence of outburst flooding on Mars

Conclusions Isotopically-depleted groundwaters at depth in the Columbia Plateau basalt aquifers were recharged 32,000 to 10,000 years before present. These waters were likely sourced from Glacial Lake Missoula floodwaters and melting of the Cordilleran ice sheet, suggesting that outburst flooding is an important recharge mechanism for groundwaters on Earth. Previous studies of landscapes on Mars show evidence for outburst flooding events (orders of magnitude larger than observed on Earth). These floodwaters may have infiltrated into underlying basalts, which are extensive at the land surface. Further studies of floodwater-basalt interactions on earth may provide important analogs for better understanding Martian hydrogeologic processes.

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