The Impact of Climate on the Physics, Hydrology, and Biogeochemistry of Crater Lake, Oregon, July 1999 – June 2004

The Impact of Climate on the Physics, Hydrology, and Biogeochemistry of Crater Lake, Oregon, July 1999 – June 2004


Primary Contact:  Gary Larson, USGS
Forest and Rangeland Ecosystem Science Center

Large, deep lakes offer a unique resource for studying the interaction of the atmosphere, land surface hydrology, and aquatic ecosystems.  heir large volume integrates the complexities of short-term variability in local climate. Thus, large lakes provide relatively manageable systems to both monitor and interpret the effects of global climate change on land surface processes. Crater Lake offers a pristine and relatively simple system to detect these changes through long-term study. It also provides a powerful natural laboratory to study the processes that link climate physics to the operation of biogeochemical cycles in aquatic ecosystems.

Crater Lake, the deepest lake in the United States (590 m), is a closed-basin caldera lake formed after the explosive eruption of Mt. Mazama, 6950 years ago. It is the center piece of Crater Lake National Park and located at an elevation of 1882 meters in the Cascade mountains of south-central Oregon.

The steep caldera walls surrounding the lake result in a very small watershed such that external flows of nutrients to the lake are low and dominated by precipitation and dry deposition from the atmosphere.  These conditions contribute to the lake’s low nutrient levels and exceptional clarity. There are no major inlet streams and no surface outlet.

The surface elevation of Crater Lake responds quickly to climate and weather fluctuations because the closed caldera functions as a giant rain gage. Annual fluctuations in elevation average about 0.5 m, but long-term declines and recoveries in lake level have been recorded since the late 1800’s.  The maximum drop (4 m) coincided with the “Dust Bowl” in the Midwest during the 1930’s. Recent climate variations have resulted in highs and lows that nearly match the historical extremes.

Changes in climate also affect lake temperatures and water circulation patterns.  In spite of its great depth, the lake mixes rapidly — over a timescale of 3-5 years — and recycled nitrogen carried upwards from the deep lake represents the largest annual source of this limiting nutrient.

This project continues our long-term study of the impact of climate on the physics, hydrology, and biogeochemistry of Crater Lake.

Continuous observations of meteorological conditions on the lake surface and caldera rim, as well as detailed water column physical measurements have been established over the past decade.

We will continue these activities, as the data they produce provide the essential input to our physical and hydrologic models of the lake. By coupling these mixing rates to a simple model of organic matter production, particle settling, and nutrient regeneration, we have demonstrated how lake physics controls the lake ecosystem in a complex way.