Crater Lake Captain Clarence Dutton was the next man to make a discovery at Crater Lake. Dutton commanded a U.S. Geological Survey party which carried the Cleetwood, a half-ton survey boat, up the steep slopes of the mountain then lowered it to the lake. From the stern of the Cleetwood, a piece of pipe on the end of a spool of piano wire sounded the depth of the lake at 168 different points. Dutton's soundings of 1,996 feet were amazingly close to the sonar readings made in 1959 that established the lake's deepest point at 1,932 feet. Crater Lake Ø It is the deepest lake in the United States Ø 7th deepest lake in the world Ø Surface area of 53.2 km2 Ø Maximum depth of 589 m Ø Mean depth of 325 m Feature Metric unit Imperial unit maximum depth (July 2000) 594 m 1,949 ft maximum depth (Year 1959) 589 m 1,932 ft average depth 457 m 1,500 ft max diameter of caldera at the rim 9.7 km (east-west) 6.02 mi (east-west) min diameter of caldera at the rim 7.3 km (north-south) 4.54 mi (north-south) surface area 52.9 km2 20.42 mi2, 13,069 acres record clarity depth (August 1994) 40.8 m 134 ft average clarity depth 27.4-30.5 m 90-100 ft Crater Lake Ø Formed by catastrophic collapse of the sides of Mount Mazama following a violent eruption about 6,800 years ago Ø Present caldera has steep walls and is between 8 and 10 km in diameter Lake Level Ø Lake level has exhibited considerable long-term variation since the late 1890's. Ø From 1910 to 1942 the lake dropped about 4 m in elevation, but returned to the 1910 level by the late 1950's. Ø The lake fluctuated by 1 m above and below a bench mark level of 1882 m observed from 1958 to 1985. Lake Level Ø Between 1986 and 1994, the level dropped to about 3.5 m below the longterm average elevation. Ø Since then the lake has risen to nearly the bench mark level. Mixing Ø The surface of Crater Lake seldom freezes over, owing to the heat content of the massive lake volume and wind mixing. Ø In winter and spring the water mass in Crater Lake circulates to a depth of between 200 and 250 m by wind action and cooling. Mixing Ø In late spring or early summer the temperature of the lake near the surface increases and a thermocline forms between July and September. Ø The depth of the epilimnion is between 5 m and 20 m. Crater Lake Ø Ø Ø Ø Orthograde nitrate-N depth profile Low concentrations of nitrate-N in the epilimnion The relatively high concentrations of total phosphorus in Crater lake is in the range usually associated with mesotrophic lakes. Some of the chemical properties of Crater lake do not conform to the entire range of criteria usually associated with oligotrophic status Crater Lake Ø Changes in the amount of chlorophyll and primary production appear to be related to deep-water mixing of the water column during winter and spring. Ø This upwelling phenomenon moves nutrient-rich waters in the deep lake to the upper 200 to 250 m of the water column. Phytoplankton Ø 157 phytoplankton taxa Ø 55 diatoms Ø 53 chrysophytes Ø 1 xanthophyte Ø 21 chlorophytes Ø 12 dinoflagellates Ø 6 cryptomonads Ø 7 cyanobacteria, Ø and 2 unknown taxa. were identified Phytoplankton Ø In winter the flora was uniformly distributed to the depth of mixing. Ø During the period of thermal stratification, phytoplankton are spatially segregated within the water column to a depth of 200 m Crater lake Ø Nitzschia gracilis was the dominant taxa in the upper 40 m of the water column. Ø Ankistrodesmus spiralis, Dinobryon sertularia, Tribonema sp., Rhodamonas lacustris and Gymnodinium inversum were the dominant taxa from 60 to 100 m. Ø From 120 to 200 m the dominant taxa were the same as during winter Zooplankton Ø During periods of thermal stratification the zooplankton were spatially segregated within the water column Zooplankton Ø Polyarthra was the dominant taxon in the upper 40 m of the lake, but it occurred in low density. Ø Between 40 m and 80 the dominant taxa were Bosmina, Polyarthra, Kellicottia and Asplanchna. Zooplankton Ø From 80 to 120 m the dominant taxa were Daphnia, Keratella, Synchaeta, Filinia and Polyarthra Ø The dominant taxa from 120 to 200 m were Philodina, Conochilus, Keratella and Collotheca. Crater Lake Ø Daphnia abundances appear linked with periods of increased primary productivity Ø Predation by kokanee salmon probably impacts their abundance and may be the reason for its reduced abundance in 1990 and disappearance in quantitative samples by 1993 Crater Lake Ø Ø Ø Ø Crater Lake was naturally barren of fish. Several salmonid species were introduced into the lake between 1888 and 1941. Kokanee salmon and rainbow trout were the only species of fish collected from the lake between 1986 and 1999. Kokanee salmon were cyclic in abundance. Rainbow trout appeared to be less cyclic in abundance than were kokanee salmon. Crater Lake Ø Kokanee salmon primarily live in the pelagic zone of the lake from the surface to a depth of about 100 m. Ø They prey on small emerging benthic macroinvertebrate pupae and larvae and terrestrial insects landing on the lake surface. Ø They also prey on Daphnia. Crater Lake Ø Rainbow trout live in the nearshore area of the lake. Ø They prey on large bodied terrestrial insects from the lake surface and benthic macroinvertebrates. Ø Rainbow trout also prey on kokanee salmon.