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Report of the Sec. of the Interior under Sec. 7 of Public Law 100-443 on the Presence or Absence of Significant Thermal Features Within Crater Lake National Park, 1992



III. Conclusions Regarding Significance of the Hydrothermal Features of Crater Lake


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A. Congressional Criteria for Determining Significance

As explained in the Introduction, Sections 2 and 6 of the Act includes Crater Lake National Park on the list of units of the National Park System containing significant thermal features. To some degree, the listing of Crater Lake National Park by the Congress supercedes this discussion of whether the hydrothermal features in Crater Lake "qualify" for significance under the criteria established by Congress under Section 6 of the Act. However, this chapter of the report addresses the significance of the hydrothermal features located in Crater Lake and will evaluate whether the hydrothermal features in Crater Lake would qualify for listing as if they were under consideration for the first time.

The Act requires the Secretary of the Interior to consider the following criteria in determining the significance of thermal features:

(1) Size, extent and uniqueness;

(2) Scientific and geologic significance;

(3) The extent to which such features remain in a natural, undisturbed condition;

(4) Significance of thermal features to the authorized purposes for which the National Park System unit was established.

The Department of the Interior provided an explanation of how these criteria would be applied to thermal features undergoing a determination of significance when it published the final list of significant thermal features in the Federal Register on August 3, 1987 (52 FR 28790). This discussion was revised to accommodate public comments received on the proposed notice published in the Federal Register in February 1987 (52 FR 4700). The Department's final explanation of how it would apply the Congressional criteria is excerpted below:

"(1) Size, extent and uniqueness - Neither lower nor upper limits on the size or extent of a feature were established. Each feature is still identified according to its existing surface dimensions. In the proposed notice, a feature could be considered significant under this criterion as long as it was identified as unique to the park unit, as well as to Region, the Nation, or-in some cases, the World. Public comments received on the application of this criterion stated that it was applied too broadly. As a result of reevaluating the application of this criterion, the Department decided that unless a feature was identified as unique to at least the Region, it should not automatically qualify as a significant thermal feature.

"(2) Scientific and geologic significance - Under the proposed notice, a feature qualified as 'significant' if the feature contributed important information to scientific or geologic knowledge, to the understanding of thermal regimes, or to the history or origin of the feature within the park unit, the Region, or the Nation. Also, the proposal considered biological factors as important to the scientific significance of a feature. The Department decided to define 'scientific significance' so as to exclude consideration of biological factors because they are considered and protected under the provisions of other laws, such as the National Environmental Policy Act and the Endangered Species Act. Also, the Department decided to narrow the qualifiers of this criterion so that only those features that satisfy the following conditions would meet this criterion: a feature must contribute to geologic knowledge compared with similar features in other areas or must make a unique contribution to the understanding of similar systems.

"(3) The extent to which such features remain in a natural, undisturbed condition - Under the proposed notice, the existing condition of identified features, described a full range of conditions, from completely undisturbed to commercially developed. As with size and extent, there were no limits established for amount or degree of development, but rather a judgment was made as to whether the amount of development was compatible with the purposes for which the park unit was established. The Department decided to limit qualification for significance under this criterion to those features which remain in a natural, relatively undisturbed condition, unless modifications were necessary to preserve a developed feature, consistent with the intent of the enabling legislation.

"(4) Significance of thermal features to the authorized purposes for which the National Park System units was created - The proposed notice considered this criterion being met if either: (a) A feature was specifically identified within the enabling legislation for the unit, or (b) a feature is being used in a manner consistent with the stated purposes for which the unit was created. The Department decided that features that are the basis for establishing the unit in the first instance (e.g., Yellowstone National Park or Hot Springs National Park) automatically meet this criterion, and that features that now significantly contribute to the statutory purposes for which the area was set aside by Congress could meet this criterion, but not automatically."

In the Geothermal Steam Act Amendments of 1988, Congress listed Crater Lake National Park as a unit containing significant thermal features. Congressional listing was effective September 22, 1988. The Department deferred its determination of significance until after the completion of research on the hydrothermal processes in the lake. Now that the studies are completed and the Department has more information upon which to base its determination, the Department determines that hydrothermal features are present at the bottom of Crater Lake and qualify as significant thermal features according to the following evaluation:

Crater Lake National Park

Feature: Hydrothermal Features Located on the Floor of Crater Lake and Associated Thermal Water Entering Crater Lake

Significance Criteria:

1. Size, Extent and Uniqueness: The size and extent of significant thermal features in Crater Lake are defined by the areal distribution of fluid inflow at sites on the lake floor, the magnitude of the thermal water inflow, and the effect of the inflow on the entire lake (area of 53 square kilometers). The areal extent of the sites of fluid inflow is indicated by large areas of bacterial mats and visually spectacular blue pools located in the south basin and off Palisade Point. The magnitude of the thermal water inflow is approximately 10% of the total inflow to the lake and the dissolved constituents in the thermal waters dominate lake chemistry. The thermal fluids result in a convective heat flow which is the second largest of the 31 thermal spring systems in the U.S. portion of the Cascades. Crater Lake is the deepest and one of the clearest caldera lakes in the world and the hydrothermal inputs and their effect on the entire lake represent a thermal feature that is unique at least to the Region.

2. Scientific and Geologic Significance - The mixing processes at Crater Lake, driven by a combination of surface heat transfer and thermal input from the inflow of thermal water from the lake bottom, are scientifically and geologically important among deep, temperate lakes of the world. The inflow of thermal water has a direct effect on the density structure of the deep lake and affects the rate of heat transport and distribution of lake constituents. Also, the studies conducted and the techniques used to describe these thermal features contribute to the scientific understanding of deep lake processes.

3. The extent to which the features remain in a natural, undisturbed condition - - The thermal features at the bottom of Crater Lake and the inflow of thermal water to the lake remain in a natural, undisturbed condition and were temporarily disturbed only to the extent necessary to conduct scientific research.

4. Significance of the feature to the authorized purposes for which the unit was created - Crater Lake National Park was established in 1902 to preserve the caldera lake and to assure the retention of its water quality (16 U.S.C. 121 et seq.). The hydrothermal inputs contribute to the properties of Crater Lake by affecting the lake's geochemical regimes and influencing the lake's mixing rates. Therefore, the hydrothermal inflow is an important contributor to lake processes and water quality.




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