Witte Hi Pt S P Geology

Run lake newton lake swartswood 2 ny k 5 c mthu nc ed

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Unformatted text preview: ial lakes, and extensive valley-outwash deposits in northwestern New Jersey. gradually to the northeast. However, at times the edge of the ice lobes remained stationary, and in a few instances readvanced southward a few miles (fig. 12). Deglaciation was probably triggered by warming temperatures that melted ice at the glacier margin faster than it was replaced by flowing ice, and by a decrease in the formation of new glacier ice due to reduced precipitation on the ice sheet. During periods when the glacier margin remained stationary, sand and gravel laid down by meltwater streams built up at and beyond the glacier margin in stream valleys and glacial lakes in 16 Minisink, Wallpack, and Kittatinny Valleys (fig. 12). Additionally, end moraines were deposited at the glacier’s terminus. Both the ice-marginal parts of the meltwater deposits and end moraines mark the former edge of the ice sheet. Mapping these ice-recessional positions enables geologists to reconstruct the geometry and retreat history of the ice sheet. The Augusta margin, which runs through High Point (fig. 12), is delineated by the Augusta and Montague moraines. The continuity of the moraines, and the size and extent of meltwater deposits laid down in nearby valleys south of the Augusta margin show that the glacier’s terminus maintained a nearly constant position for more than a hundred years. Erosion by Ice Features carved in bedrock by moving glacial ice are numerous in the park. They include striations, crescentic marks, polished bedrock, and plucked outcrops. Striations are linear scratches and grooves cut in bedrock by overriding ice that show the direction of glacial movement. They formed in places where hard stones, frozen to the bottom of the glacier, scraped across the underlying bedrock. Striations are also found on stones that have been glacially transported. Crescentic marks, which include gouges, fractures, and chatter marks, are cracks and chips in the rock surface made when stones at the glacier’s base exerted great pressure on the underlying rock. Striations and crescentic marks in the...
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