Monitoring Surface Moisture of Crater-fill Sediment in Extreme hydroclimatic conditions (Ubehebe Volcanic Field, Death Valley, California).

Abstract:

The long term monitoring of soil surface moisture is key for constraining surface hydrology processes in extreme weather and climatic settings and their impact on biological and geological components of desert environments. We tested and applied the use of miniature data loggers to acquire novel Temperature (T) and water content (weight percent, wt%) of fine-grained sediments deposited during rain events at Ubehebe Crater (UC), the larger and deeper crater within a volcanic field in Death Valley. The Miniaturized in situ systems are compliant with Death Valley National Park’s regulations to conduct scientific research in wilderness and sacred sites.

 About 130,000 hours of recorded soil moisture and temperature were acquired in relation to the hydroclimatic conditions (2009-current). Total annual rainfall in the area range from ~50mm to <250 mm/y in water years (WY) 2004-to date. These values are representative of the climatic context of the Mojave Region as they encompass the wettest (2005, 2011) and driest years (2002, 2007, 2012, 2013, 2014) of the last ~120 years (Western Regional Climate Center, www.wrcc.dri.edu). To date, surface (0.5 cm to 2 cm-depth) moisture of intra-crater deposits can vary from dry-very dry (1-3wt % to - 10 wt%) to wet-saturated (10-60 wt%). Over saturated conditions occur in ephemeral ponds, which appear to form once a year as a result of winter and summer rainstorms, and may last for one-two weeks (2009-2014 study years).

Summer storms can yield ca. 40% to 60% of the total annual precipitation (WY 2011 thru 2014). The intensity and temporal distribution of annual storms together with ground temperature extremes (-16 to +67 ºC) influence moisture distribution and retention within the crater’s floor.