Temperatures of springs in the vicinity of Crater Lake, Oregon, in relation to air and ground temperatures by Manuel Nathenson, 1990


Measurements of temperature, specific conductance, and flow have been made for many of the springs in the vicinity of Crater Lake (Figure 3 and Table 3). Temperatures were measured using a thermocouple thermometer (Omega Engineering Model 871) with 0.1C electronic digital readout Temperatures from the thermocouple and readout device were compared to a 0. 1°C mercury-in-glass thermometer in a well-stirred beaker of water and found to be within 0.20C over the range 1° to 15’C, both before and after the field trip. Spring temperatures were measured by placing the thermocouple in the orifice. Specific conductance was measured using a digital conductivity meter (Whatman CDM 300) with automatic temperature compensation of 2% per IC. Comparison to standard solutions at 74 and 718 pS/cm showed the meter and cell to agree to the standard solutions to within 3%. Specific conductance was measured either in the spring orifice or slightly downstream. Elevations were obtained from 1:24,000 topographic maps to the nearest contour (40, 20, 5, or 1 foot depending on the map). Spring flows were obtained by measuring a representative depth (in a few cases several depths were measured) and a representative width to obtain a cross-sectional area and measuring speeds by timing the passage of a floating object over a measured distance. This method of measuring flows is inherently limited in accuracy and precision, and flows are probably only known within ±50%.

Figure 4 shows the measured temperatures plotted versus elevation. It has previously been established that the source of the Wood River and other springs in the eastern Wood River Valley are anomalous in chemical constituents compared to the water in other springs (Nathenson and Thompson, 1990). Data for these springs are shown using special symbols in Figures 3 and 4 and will be discussed as the Wood River group. Springs in the western Wood River Valley along with Cedar Spring provide a useful comparison to the Wood River group and are combined as the Cedar Springs group. Except for about half the data for the Wood River group, nearly all of the spring temperatures in Figure 4 plot below the best-fit air line and even below the lowest air temperature measured. Spring temperatures, like air temperatures, increase with decreasing elevation. Most of these springs probably fit Meinzer’s definition of a cold spring. Excluding the Wood River group, spring temperatures average 1.9±1.0 0C cooler than the air temperature line.

Some of the temperatures that have been obtained in this study are significantly cooler than those published by Thompson and others (1990). Many of the temperatures in that study were collection temperatures rather than orifice temperatures. This is especially true for samples from within the crater walls, where the orifice was physically difficult to get to.

Also shown on Figure 4 is a temperature profile for Crater Lake obtained in June 1971 (Neal and others, 1972). The upper 300 m of Crater Lake has large variations in temperature in response to winter cooling and summer heating, but the profile was measured at a time of year when these effects are minimal. The important temperatures are those in the bottom half of Crater Lake, which do not vary seasonally and represent an annual average. These temperatures are similar to those for nearby cold springs and indicate that the lake is neither particularly cold nor hot compared to its surroundings.

On Figure 4, the springs of the Wood River group are shown separated into the source of the Wood River and the remainder of the group. The source of the Wood River is a large pool with numerous vents aligned along an z800-m linear, and data obtained at several of these vents cover a significant range in temperature (Figure 4). Orifice temperatures for about half of the Wood River group are significantly warmer than the best-fit air line and appear to be significantly warmer than the trend of other springs on Mount Mazama and springs at the same elevation in the Cedar Springs group.

To gain perspective on the anomalous temperatures for springs in the Wood River group, it is useful to look at the variation of specific conductance. Figure 5 shows specific conductance versus temperature, and Figure 6 shows specific conductance versus elevation. Nathenson and Thompson (1990) have shown that the chemistry of most springs on Mount Mazama is fairly similar, because it is produced by the weathering of volcanic glass and clinopyroxene. The plot of specific conductance versus temperature indicates that the total dissolved solids correlates well with temperature. Temperature may not actually be the determining factor for the amount of dissolved solids, but it could reflect another mechanism for degree of reaction, such as increasing distance from source to exit at lower elevations. The plot of specific conductance versus elevation shows that specific conductance generally increases with decreasing altitude, just as temperature does, but that the springs of the Wood River group do not follow this relationship. Nathenson and Thompson (1990) have shown that these springs are different from other springs in the area in having significant amounts of dissolved chloride and sulfate, and there has to be an additional mechanism beyond weathering to explain their chemistry. The range of temperature and specific conductance for the springs of the Wood River group reflects mixing of two waters: one that is warm and slightly saline with another that is cool and less saline.

The general chemical characteristics of the springs of the Wood River group are similar to those of Crater Lake (Nathenson and Thompson, 1990). Their respective chloride fluxes can also be compared as a possible indicator of the flow of thermal water (Mariner and others, 1989). Table 4 presents an inventory of chloride flux for the Wood River group. The total flux is 34,000 mg/s. Mariner and others (1989) have also measured the chloride flux for the eastern Wood River Valley using different measuring points and a different methodology to establish the anomalous chloride; they found a higher flux of 60,000 mg/s. Nathenson (1990) has done a chemical balance for Crater Lake and found that the anomalous chloride input is 24,700 mg/s. Thus the chloride flux from the Wood River group is larger than the input to Crater Lake. Temperatures for the Wood River group indicate that the chloride flux is associated with a significant thermal anomaly; however, the available data are inadequate to quantify the thermal anomaly in terns of energy output.