Nature Notes

Volume XXIV - 1993

Drought and the 1992 Pond Survey
By Roger Brandt


The summer of 1992 arrived with a combination of circumstances that may earmark this season as having the most extreme drought conditions ever recorded in the history of Crater Lake National Park. Two factors were instrumental in making this happen. First, Crater Lake National Park experienced a very dry winter and spring from December 1991 to May 1992, with snowfall for that period being 45 percent of the average amount. This has a historic significance because it marks the lowest accumulations of snowfall in the 60 year weather record of Crater Lake National Park. Second, the summer of 1992 marks the sixth consecutive year of drought in this region, though below average precipitation has been the rule for all but three years in the past fifteen. Inasmuch as the park's surface water resources were already under stress, the record low snowfall of this winter and spring intensified the scenario.

Six Ponds That Survived the Drought

Twenty eight ponds are located inside the boundaries of Crater Lake National Park, with most situated in the western half of the park. The majority of these ponds have depths of two to four feet when filled with water and have maximum diameters ranging from 30 to 200 feet. Spruce Lake is the largest of the ponds, with a maximum depth of about 12 feet end a length of over 300 feet. Several ponds in the Sphagnum Bog area and on Whitehorse Bluff have maximum depths of six to eight inches and diameters of 20 to 50 feet. All of the ponds appear to be filled only by direct rain or snowfall rather than by surface water. Some subsurface inflow is a possibility in a couple of ponds. The ability of these ponds to sustain appreciable water levels through the dry summer seems to be governed by the substrate that forms the basins where these ponds are located. Ponds which are poised in depressions on the surface of lava flows, like Quillwort Pond and Whitehorse Pond #3, for example, are the most persistent, whereas ponds poised in pumice fields from Mount Mazama's climactic eruption, like Spruce Lake and Lake West, are the least persistent.

During the summer of 1992, it is likely that only six of the twenty eight ponds in Crater Lake National Park did not dry up before the first substantial storms came in mid October. These ponds are listed in the table and can be found on the I :62,500 topographic map of the park published by the U. S. Geological Survey. The figures delineate the locations of ponds in the Sphagnum Bog and Whitehorse Bluff areas.

Sphagnum Bog #29 Aug 19921 ft. May have received subsurface water from Sphagnum Bog Pond #3
South of Castle Point25 Aug 1992 8-10 in.Large salamander population
Whitehorse #22 Sept 1992 1 ft.May be receiving subsurface water from Whitehorse Pond #3
Whitehorse #32 Sept 1992 2+ ft.Possibly the most robust pond in the park
Quillwort Pond24 Aug 1992 2 ft.Water level was about the same when observed by others in mid-October
North of Pumice Flat10 Aug 1992 2+ ft.Heavily used by elk
Most persistent ponds of Crater Lake National Park. (see maps for the numbering system used with ponds in the Sphagnum Bog area and on the Whitehorse Bluff.)
sketch map of Sphagnum Bog ponds
Sphagnum Bog ponds

sketch map of Whitehorse Bluff ponds
Whitehorse Bluff ponds

Lake Level Bottoms Out
By Thomas McDonough

The lowering in the surface level of Crater Lake recorded during the last few years could be over. A return to a more average winter pattern where snowfall amounts exceed 500 inches has already been realized in 1992-93. This snowpack, and any additional precipitation, should all but stop the decline in lake level observed since 1986.

The rise and fall of Crater Lake's level this century is connected closely to the fluctuations in the region's weather. Lake levels have been observed and recorded since early this century. Crater Lake was at its deepest in March of 1975 when the lake level measured 6179 feet above mean sea level. This is 16 feet above its lowest point, which was measured in early September of 1942. In 1959, when the U.S. Geological Survey measured the depth of the lake and found it to be 1,932 feet deep, the lake level was 6,176 feet above sea level. This is a good indication that the lake level is always in flux.

Lake level is primarily affected by annual precipitation. For the lake to retain the same level observed the year before, 66 inches of precipitation must be recorded at Park Headquarters. This would come largely as snow and approximates to roughly 530 inches of annual snowfall. If more is received, the lake will be higher during the following summer. If less is recorded, the lake level will fall. A declining lake level has been the case for the last six years. Only 243 inches of snow fell from July 1, 1991 to June 30, 1992. In late September of 1992, at the end of the water year, Crater Lake's level fell below 6,169 feet. This is close to levels seen in the 1940s and therefore represents a fifty year low. Crater Lake has, however, not been alone among lakes in the region. Upper Klamath Lake and reservoirs throughout southern Oregon also dropped to levels not seen for decades.

If precipitation patterns observed earlier this century are used, Crater Lake will require six years of greater than average snowfall to regain the volume of water lost since 1986. It is likely that the lake will take many more than six years to reach higher levels again. Forecasting future weather patterns and associated lake levels is, at best, risky. Nevertheless, we seem to be at the end of a dry cycle that has been expressed by a drop in Crater Lake's surface level.

Crater Lake Surface Variation
September 30th
chart showing Crater Lake surface variation
Observed elevation of the lake surface this century. The surface elevation of 6,176 feet is 1,932 feet above the deepest part of the lake. Gaps in the chart are due to periods when measurements were not taken.

<<< Previous
> Cover <
Next >>>