Marble Mountains Research Projects

Jerry Davis
Dept. of Geography & Human Environmental Studies
San Francisco State University

(1) Collection and analysis of deposits from cave systems

The major focus of this part of the study will be on caves developed in a 60-km intermittent band of marble extending from the Marble Mountains of Siskiyou County, California, to Oregon Caves National Monument of Josephine County, Oregon. I have identified three sites so far in the Marble Mountains with sediment and/or carbonate sequences suitable for analysis. Cooperation with Steve Knutson (Co-Director) and other members of the Klamath Mountains Conservation Task Force (KMCTF), currently exploring the significant cave systems here, will prove useful in identifying further sites. This cooperation has already proved fruitful in karst process studies (see below); Knutson and others are quite interested in the results and willing to provide field assistance. Initial contacts with Interpreters at the Oregon Caves National Monument show promise of cooperation at that site as well.

Preliminary investigations of Marble Mountains deposits have shown that karst and cavern development spans known cycles of glaciation in the area: two carbonate samples are at least 350,000 years ago, based upon 230Th/234U dating of flowstone from one of the older, upper caves in the area; calcite deposition also occurred around 90,000 years ago, from a sample in a lower, more recent cave. Calcite deposition continues in caves in mantled karst. I believe that significant cavern development and decoration predate major events of glacial removal of overlying soils. A better understanding of the patterns and magnitude of modern processes will provide a unique picture of a developing karst-glacial landscape.

Analysis of sediments and carbonate precipitates will include:

(a) Dating of materials using isotope, magnetostratigraphic, and chemical fingerprinting methods. A recently published chronology, by Rieck and others (1992), of a lake sediment core from Tulelake, California, to the east of my study area, shows great promise in providing dateable benchmarks for materials collected in the Marble Mountains and other caves in the region. Two U.S. Geological Survey specialists who worked on the Tulelake core have expressed interest in cooperating in this project: Andrei M. Sarna-Wojcicki (chemical fingerprinting) and David P. Adam (Quaternary climatic change). We hope to gain funding support to cover costs of sample analysis through a campus mini-grant and matching support from the U.S.G.S. Global Change and Climate History Program.

(b) Pollen analysis (palynology) of sediments and carbonate speleothems. Pollen recovered from samples have been widely used with lake sediments for interpreting past vegetation patterns and climates. At the University of Georgia, I worked with George A. Brook on developing methods for analyzing pollen from carbonate speleothems (Davis and Brook, 1979), and the techniques have been further developed and applied in caves in various parts of the world, especially North America and Africa. Brook has offered to collaborate on this project, in fact has already provided assistance with the preliminary Uranium series dates described above. The need for more local pollen expertise (since understanding modern pollen assemblages is the first step in interpreting past assemblages) has led me to Roger Byrne (U.C. Berkeley Geography), a palynologist specializing in Sierra Nevada flora, and another cooperator on this project.

(c) Sediment size and compositional analysis. Any analysis of a sample from a sediment sequence must be made in the context of the environment under which the sediments were deposited. Cave deposits can be derived from materials carried in flowing water in cave streams, air moving between entrances, or percolating groundwater. The nature of the transportation system can be evaluated by looking at variations in sediment particle sizes, and the source of sediments can be derived by looking at their mineral composition. With minor additions, a laboratory in the SFSU Geography Department can be used for size analyses; composition will be analyzed at the USGS.

(2) Investigation of modern glaciokarstic analogs

Evidence for coupled glacial and karst processes in the Marble Mountains leads the geomorphologist to seek out areas in which these processes are currently active. One of the most compelling sites is the Castleguard Karst, where the eponymous cave is still forming under the Columbia Ice Field in western Alberta. Investigators from McMaster University (Hamilton, Ontario), including Derek Ford, have explored passages that extend under the ice itself. Clearly we see a modern analog to what would have happened in the Marble Mountains of 15,000 years ago.

(3) Karst process studies

Research in the Marble Mountains since I initiated study in August 1990 has focused on developing an understanding of the geomorphic and environmental processes that continue to shape this alpine karst landscapes. Though many geomorphic processes are at work, the dominant process in the Marbles appears to be the solution of marble by acids in snowmelt and soil water. Yet we know very little about basin-wide erosion rates or the impact of seasonality. We don't know how much this landscapes result from modern processes or, conversely, from ancient conditions that are presently inactive (e.g. glacial processes). In the Marble Mountains, I hope to develop a model of the modern geomorphic systems and the seasonal patterns in erosional processes.

Research under way in the Marbles includes:

(a) Field reconnaissance of surface and subsurface landforms and hydrological systems.

(b) Analysis of spatial variations in the solution chemistry of surface and subsurface streams during low-flow summer conditions. I directed a graduate student -- Adrian Sears -- in his thesis research of this question, and he has been able to document such variations through the analysis of water samples from 50+ sites during August 1991. Spatial variations in water chemistry variables -- water temperature, pH, electrical conductivity, concentrations of Ca++, Mg++, SiO2, and Cl-, and derived values of alkalinity and mineral saturation indices -- have demonstrated that bare karst (not covered by soil) appears to be eroding more slowly than nearby soil-mantled karst. Glacial processes, though intermittent and not presently active, are probably more significant in the bare karst areas.

(c) Analysis of temporal and seasonal changes in the solution chemistry of the area. An important aspect of erosional and environmental processes is how these change over time, and how they relate to annual cycles of solar radiation, temperature, precipitation, and runoff (in this area produced primarily by snowmelt). Such measurements have consistently proved difficult in remote alpine areas, resulting in an absence of continuous data from these environments. We have identified a major groundwater resurgence in the Marbles that can be used for this type of study, and we have been able to document its solution chemistry during the low-flow season of late summer and early fall, when the area is relatively accessible. A data logging system at the resurgence, first attempted for the 1991-92 season but destroyed by bears, has been redesigned and is now in place and operational, with over a year of data collected so far, and continues to collect data including total dissolved solids (TDS), water level, and air and water temperature.

Samples collected during site visits are analyzed for additional parameters -- alkalinity, mineral saturation indices, and concentrations of calcium, magnesium, sulfate, and silica -- that cannot be recorded using a data logger. These data are used to generate multivariate statistical models to predict values for these parameters from the logged variables.

(d) Analysis of seasonal and spatial variations in soil CO2. To date, multiple samples have been collected from over 30 sites established throughout the study area, and clear spatial and seasonal patterns are emerging. While the purpose of this study is to understand spatial and seasonal patterns in karst solution processes, there is a clear relationship to biotic patterns of flowering, with maximum values during the month following the release of the soil from snowcover in the spring and summer. The results so far are of an exploratory, reconnaissance level -- more detailed (in space and time) studies are proposed.

(4) Initiation of snowmelt mechanism studies

The major focus of the proposed research is to evaluate climatic change as it has impacted the region, geomorphologically and biogeographically. A major impact has been the growth of glaciers in response to changes in environmental conditions. Today, no actual glaciers occupy the area, but there is evidence that significant glaciers advanced in Marble Valley and other areas as recently as the Neoglacial (3000-2000 years B.P.) and today in most years ice remains in deep shaded depressions throughout the year. There is obviously a link between glacial cycles and changing climates, and obviously increased snowfall or decreased melting would cause glaciers to grow, but the exact nature of the glaciation-climate link is not completely clear. Jack McConchie's research (pers. comm.) into the meltwater response of Antarctic ice fields casts considerable doubt on the conventional wisdom that warmer temperatures are the cause of glacial recessions, but his results must be evaluated in other parts of the world. My discussions with Jack have led to plans of extending these studies to the Sierra Nevada and Klamath Range.

Part of my proposed research will be to initiate meltwater mechanism studies in Marble Valley, where the relationship between environmental measures and snowmelt can be monitored.

(5) Larger regional study proposal