Regional Landscape Ecosystems of Michigan, Minnesota, and Wisconsin
SUBSECTION IX.7. Keweenaw
DISCUSSION: Subsection IX.7 is distinguished from adjacent subsections by its strongly lake-influenced climate, which results in a relatively long, cool growing season and heavy lake-effect snowfall. The volcanic bedrock forms steep, exposed bedrock ridges throughout much of the subsection.
SUB-SUBSECTIONS: The Gay sub-subsection (IX.7.1) has coarse-textured, broad ridges over sandstone; the Calumet and Isle Royale sub-subsections (IX.7.2, IX.7.3) have steep ridges of volcanic bedrock.
ELEVATION: 602 to 1,490 feet (183 to 454 m).
AREA: 1,365 square miles (3,535 sq km).
STATES: Michigan.
CLIMATE: Climate in the north is strongly affected by lacustrine influences; this lacustrine influence is somewhat less in the southern interior. Except for air masses from the southwest, all air masses pass over Lake Superior before reaching this subsection, resulting in a relatively long, cool growing season (Albert et al. 1986). Winter temperatures are moderated by Lake Superior, but this effect drops off rapidly at the south end of the subsection; extreme minimum temperature is -34½F along Lake Superior (Eichenlaub et al. 1990). Heavy lake-effect snowfall, ranging from 140 to more than 200 inches, characterizes the subsection. Average annual precipitation is 32 inches.
BEDROCK GEOLOGY: Erosion-resistant Precambrian conglomerates and amygdaloidal basalt form the steep ridges along the northern half of the Keweenaw Peninsula and on Isle Royale (Dorr and Eschman 1984, Reed and Daniels 1987). Between the ridges are depressions formed from veins of more easily eroded lavas. Freda sandstone and Nonesuch shale are exposed along the northern half of the Keweenaw Peninsula; the Jacobsville sandstone (also of Precambrian age) forms the southern half of the peninsula.
The bedrock ridges of the Keweenaw Peninsula and of Isle Royale are part of the Lake Superior syncline, which extends from northern Wisconsin to the tip of the Keweenaw Peninsula of Michigan.
LANDFORMS: Gay sub-subsection (IX.7.1): broad ridges of sandy till. Calumet (IX.7.2) and Isle Royale (IX.7.3) sub-subsections: steep, linear bedrock ridges, lakes, and wetlands. See sub-subsections.
LAKES AND STREAMS: See sub-subsections.
SOILS: See sub-subsections.
PRESETTLEMENT VEGETATION: See sub-subsections.
NATURAL DISTURBANCE: See sub-subsections.
PRESENT VEGETATION AND LAND USE: See sub-subsections.
RARE PLANT COMMUNITIES: See sub-subsections.
RARE PLANTS: See sub-subsections.
RARE ANIMALS: See sub-subsections.
NATURAL AREAS: See sub-subsections.
PUBLIC LAND MANAGERS: See sub-subsections.
CONSERVATION CONCERNS: See sub-subsections.
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