Data for precipitation at the Mammoth Ranger Station, streamflow at the Hot Creek flume, and water levels in cold-temperature wells SC-1 and SC-2 are useful references for variations in surface-water runoff and related ground-water recharge in the caldera.
In general, the shallower the well and aquifer that it penetrates, the more closely the well hydrograph resembles the streamflow hydrograph. This effect is demonstrated by a comparison of wells SC-1 and SC-2, which were drilled at the same location to depths of 40 m and 70 m, respectively. Both wells are perforated in permeable basalt formations, the deeper basalt formation in SC-2 being separated from the formation in SC-1 by a 10-meter-thick layer of less-permeable glacial till. The effect of the till layer is to dampen the magnitude of the seasonal changes in hydaulic head (as measured by changes in water level) induced by recharge from the land surface, and to amplify the effects of longer-term variations in recharge.
The long-term response of water levels in each well is dominated by variations in annual precipitation, which caused relatively high water levels in 1983-1986, an extended period of declining water levels in 1987-1994, and a period of steadily increasing water levels from 1995 to the present.
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