ill.; Three folded plates in pocket; Thesis (M.S.)--University of Minnesota, 1961; Bibliography: leaves 168-175
ABSTRACT Crater Lake which is 1,932 feet deep is located in the collapse caldera of Mt Mazama in the High Cascade Mountains, Oregon+ Past and present geologic and liinnologic processes are described and the sequence of events of lake history is outlined* Bottom sampling guided by the 1959 chart of the Coast and Geodetic Survey, was accomplished with dredges and a corer* Laboratory analyses of pH, Eh, moisture content, permeability, particle size, mineralogy, pollen, flora and fauna were made, and published and unpublished reports were reviewed* Study revealed a submerged basaltic-andesite cinder cone (Merriam Cone) and a submerged dacite dome* Cone locations indicate that Merriam Cone formed first and the emergent Wizard Island last* The position and sub-aerial nature of the cones indicates that lake filling lagged behind eruptive activity# The lake may be 1,000 to over 7,000 years old since volcanic activity may have ceased at any time during this period* Homothermal winter conditions may allow the greatest water circulation, but summer finds surface-water temperatures up to 18*3°C, non-uniform temperature shear-zones, and hypolimnion water below 100 meters at 4°C or less* Water circulation other than sublacustrine slide and wind surface currents is poorly understood* Water purity causes unusual transparency, color, and biota distribution* Because precipitation is the main water source and because the basin is enclosed by volcanic rocks, the water has a relatively low content of dissolved solids with proportionately high amounts of chlorine, silica, and sulphate and low amounts of carbonate, organic nitrogen, and organic phosphorus* Alkaline surface pH to neutral bottom pH, slightly reducing to neutral Eh of the sedimentary environment, and low organic productivity are related to water chemistry, organic activity, and bottom environment* The lake setting limits the natural introduction of species and thus cosmopolitan forms characterize the native biota* Mans1 intentional and accidental introduction of species causes an artificial increase in organisms* The pelagic community contains a surface scum of insects and pollen, a plankton assemblage of vi algae with some Daphnia, and a nekton of planted fish© The littoral environment is divided into the harsh eulittoral zone that has shelled the encrusting organisms and the sublittoral zone that has in addition benthonic Protozoa* Porifera* Nematomorpha* Annelida, Mollusca* and Arthropoda* The biota of the littoral zone reaches a depth of 425 feet in the form of moss. It can be subdivided into protected and open-shore littoral assemblages* and is reduced near stream entrances due to fine suspended sediments© Life is nearly absent on the rocky steep bathyal slopes from 425 feet down to the flat abyssal plains over 1*800 feet* All evidence indicates that Grater Lake is a classic example of an oligotrophic lake and may never change « The steep-walled caldera with volcanic layers that can erode rapidly and with cones that protrude from the flat floor has mainly allochthonous sediments* Slides are generally responsible for the erosion of sediment above and below the water« Lake deposits are scattered on the caldera slope and are found mainly on the flat lake floor, where they consist of sandy muds with interbeds of well-sorted fine sand* Deposits are unconsolidated with up to 87$ water, but colloidal clay apparently causes low permeability and a sealing by lake ooze for some of the basin* Grater Lake sand layers do not have all the usual features of turbidity-current deposits, but experimental findings may explain this lack* Deposits similar to those of the Southern California coastal troughs imply similar transport processes* Apparently the coarse materials periodically slump rapidly to the slope bottom where a transition to turbidity currents occurs and fine well sorted sands are carried in restricted flows over the flat basins* Sand layers can be separated by mineralogy, even within single cores • In some cases mineralogy relates individual layers to specific sources* The mineralogy of the submerged flows east of Wizard Island is unique; distribution of the unusual fragments seems to indicate that altered Wizard Island flows nearly surround the protruding dacite dome. vii Autochthonous moss and diatoms, as well as wind-transported pollen are the main organic constituents of the sediments Uniform pollen spectra are found in all bottom sediments even though different vegetation zones surround the lake* Spectra are not representative since mountain hemlock is dominant in most of the adjacent forests, whereas over 10% of the total pollen is pine, mainly from local pine* Uniform pollen spectra allow no dating nor determination of sedimentation rates• Additional studies of water chemistry, deep lake sediments, and bog deposits possibly formed by Crater Lake seepage may solve problems of limnology such as water circulation, and lake history* viii
ABSTRACT Crater Lake which is 1,932 feet deep is located in the collapse caldera of Mt Mazama in the High Cascade Mountains, Oregon+ Past and present geologic and liinnologic processes are described and the sequence of events of lake history is outlined* Bottom sampling guided by the 1959 chart of the Coast and Geodetic Survey, was accomplished with dredges and a corer* Laboratory analyses of pH, Eh, moisture content, permeability, particle size, mineralogy, pollen, flora and fauna were made, and published and unpublished reports were reviewed* Study revealed a submerged basaltic-andesite cinder cone (Merriam Cone) and a submerged dacite dome* Cone locations indicate that Merriam Cone formed first and the emergent Wizard Island last* The position and sub-aerial nature of the cones indicates that lake filling lagged behind eruptive activity# The lake may be 1,000 to over 7,000 years old since volcanic activity may have ceased at any time during this period* Homothermal winter conditions may allow the greatest water circulation, but summer finds surface-water temperatures up to 18*3°C, non-uniform temperature shear-zones, and hypolimnion water below 100 meters at 4°C or less* Water circulation other than sublacustrine slide and wind surface currents is poorly understood* Water purity causes unusual transparency, color, and biota distribution* Because precipitation is the main water source and because the basin is enclosed by volcanic rocks, the water has a relatively low content of dissolved solids with proportionately high amounts of chlorine, silica, and sulphate and low amounts of carbonate, organic nitrogen, and organic phosphorus* Alkaline surface pH to neutral bottom pH, slightly reducing to neutral Eh of the sedimentary environment, and low organic productivity are related to water chemistry, organic activity, and bottom environment* The lake setting limits the natural introduction of species and thus cosmopolitan forms characterize the native biota* Mans1 intentional and accidental introduction of species causes an artificial increase in organisms* The pelagic community contains a surface scum of insects and pollen, a plankton assemblage of vi algae with some Daphnia, and a nekton of planted fish© The littoral environment is divided into the harsh eulittoral zone that has shelled the encrusting organisms and the sublittoral zone that has in addition benthonic Protozoa* Porifera* Nematomorpha* Annelida, Mollusca* and Arthropoda* The biota of the littoral zone reaches a depth of 425 feet in the form of moss. It can be subdivided into protected and open-shore littoral assemblages* and is reduced near stream entrances due to fine suspended sediments© Life is nearly absent on the rocky steep bathyal slopes from 425 feet down to the flat abyssal plains over 1*800 feet* All evidence indicates that Grater Lake is a classic example of an oligotrophic lake and may never change « The steep-walled caldera with volcanic layers that can erode rapidly and with cones that protrude from the flat floor has mainly allochthonous sediments* Slides are generally responsible for the erosion of sediment above and below the water« Lake deposits are scattered on the caldera slope and are found mainly on the flat lake floor, where they consist of sandy muds with interbeds of well-sorted fine sand* Deposits are unconsolidated with up to 87$ water, but colloidal clay apparently causes low permeability and a sealing by lake ooze for some of the basin* Grater Lake sand layers do not have all the usual features of turbidity-current deposits, but experimental findings may explain this lack* Deposits similar to those of the Southern California coastal troughs imply similar transport processes* Apparently the coarse materials periodically slump rapidly to the slope bottom where a transition to turbidity currents occurs and fine well sorted sands are carried in restricted flows over the flat basins* Sand layers can be separated by mineralogy, even within single cores • In some cases mineralogy relates individual layers to specific sources* The mineralogy of the submerged flows east of Wizard Island is unique; distribution of the unusual fragments seems to indicate that altered Wizard Island flows nearly surround the protruding dacite dome. vii Autochthonous moss and diatoms, as well as wind-transported pollen are the main organic constituents of the sediments Uniform pollen spectra are found in all bottom sediments even though different vegetation zones surround the lake* Spectra are not representative since mountain hemlock is dominant in most of the adjacent forests, whereas over 10% of the total pollen is pine, mainly from local pine* Uniform pollen spectra allow no dating nor determination of sedimentation rates• Additional studies of water chemistry, deep lake sediments, and bog deposits possibly formed by Crater Lake seepage may solve problems of limnology such as water circulation, and lake history* viii