Edges And Surfaces Of Rock Bodies example essay topic

New York's Geology The bedrock of the earth is made up of rock bodies that vary in size, shape, orientation, composition, color, and texture. These rocks makeup the bedrock, which is present everywhere. If one were to study a map of the bedrock from a versicle point of view, they would find that patterns are made by eroded edges and surfaces of rock bodies that crop out of the state. Most rock bodies are originally tubular and horizontal. Deformations of these rock bodies occur over many years due to tilting, folding, crumpling, and breaking. An example of this can be found in the rock bodies of western New York.

It is composed of layers of sedimentary rocks, all diffrent in thickness, that are tilted down south less then 1 degree resulting in widths of out cropped bands. The Adarondac Mountains were once tubular rock bodies, but now sweep into broad folds. This deformed-rock pattern is typical of highly metamorphosed basment rock. One can easily see this rock pattern continue in the basment as it passes beneath the b; an ket of sedimentary strata that surrounds the mountains. The pattern of small blocks along the eastern border of the adirondack results from faulting that dropped crustal blocks down into a gain staircase. The Taconic Mountains east of the Hudson River Valley are huge slices of crust that were thrust into that area from the east.

The heavy toothed lines show the edges of these thrust sheets. The earth's crust in this region was "telescoped" when a volcanic island arc collided with the edge of the continent, causing what is known as Taco nian orogeny. This collision compressed the layered rock and sediment of the intervening sea, thrusting them westward onto the continent as huge, stacked -slices. The slices, which generally dipped east in a shingled arrangement, were contorted considerably in the process. When completed, the stack extended from New England past the western edge of the Hudson Valley. In the Catskill Mountains, the western edge of this transported rock remains buried beneath Devonian rock.

Erosion has reduced the original thrust sheets to patches, creating windows to the rock beneath. For the most part New York's bedrock is covered by soil and other loose material, this is especailly true in area's with humid climates. This soil and other material is a result of the weathering of surfical rocks. This regolith can remain in place, but is usually eroded, transported, and deposited by water, wind, or glacial ice. 90% of New York state bedrock is covered by surfical deposited that one more then 1 meter thick. Most of these deposits were left by a continental glacier - an ice sheet.

The most abundant glacial deposit is Till. Till is compossed mostly of mud, sand, gravel, cobbles and boulders that the glacier spread over the countryside. Till can be up to 50 meters thick. Moraines are elongate ridges or strings of hills that formed at the edge of the glacier and are compossed of Till. An example of this can be found in the Ronkonkoma and Harbor Hill Moraines in Long Island. To better understand this section refer to the physographicand tectonic maps attached to this paper This physiographic map illustrates the rich variety of landforms in the northeastern United States and adjacent Canada.

The various landforms are mainly the result of weathering and erosion, which attack different types of rock at different rates. Lowlands form on easily erodible rocks, highlands on resistant ones, with all gradations between. The distribution of rock types in a region strongly influences its physiography. The matching tectonic map shows the diverse structure of the region's bedrock. A comparison of the physiographic and tectonic maps clearly shows how much the physiography depends on bedrock geology. Continental glaciation played a big role in the development of New York's landscape in the recent geological past.

On its far south, the glacier removed and transported soils and eroded the surface of the bedrock. As the ice melted, this debris (mud, sand, gravel, and boulders) was left at new sites in a great variety of depositional landforms. Melting caused the glacier to retreat across the State from south to north between 20,000 and 10,000 years ago. The hilly area in the north-central part of the map is the Grenville Province of the Canadian Shield, an area of basement rocks, which extends across the narrow Frontenac Arch into the Adirondack Mountains.

The harder rocks in the arch eroded more slowly than those around them and formed the Thousand Islands in the St. Lawrence River. Present-day drainage features in the Adirondacks illustrate well glacial erosion, transportation, and deposition. The continental ice sheet converted many pre-glacial river and stream valleys into chains of lakes by carving rock basins during ice advance and by depositing earth dams during ice retreat. The prominent northeast-trending rivers, streams, and lakes occur where faults and fracture zones greatly weakened the bedrock to make it easily eroded. In the low plains south and west of the Canadian Shield, bedrock is covered by glacial till and by layers of sand and mud deposited in meltwater lakes.

This area is underlain by flat layers of sedimentary rock and is part of the Interior Lowlands, which extend westward to the Great Plains. Immediately south of Lake Ontario is a remarkable field of streamlined hills of glacial till called drumlins, some of which are shown west of Syracuse. East of Lake Ontario, elevations increase to form the Tug Hill Plateau. South of the lake and across the Mohawk Valley, the land surface rises to form the Allegheny Plateau. This plateau forms the northern end of the extensive Appalachian Plateaus, which extend to the southwest. The plateau boundary curves eastward across New York south of Rochester and Syracuse, to the Helder berg Escarpment southwest of Albany.

The plateau surface rises in this direction until it becomes the Catskill Mountains. Rivers and their tributaries have cut the originally level Appalachian Plateaus into hilly uplands. The branching drainage pattern typically is developed by streams eroding horizontal layers of rock. Some of the north-south stream valleys were broadened and deepened by glacial ice, then dammed by glacial debris to form lakes. The Finger Lakes south of Lake Ontario were formed in this way. The two largest Finger Lakes, Seneca and Cayuga, are labeled.

Southeast of the Appalachian Plateaus is the Appalachian Valley and Ridge Province, a belt of sinuous ridges that curves northward through Virginia and most of Pennsylvania. Here the carpet of sedimentary rocks, was buckled into tight folds during the last Appalachian mountain-building episode. Farther southeast is the Great Valley, a lowland created largely by groundwater and surface water slowly dissolving the carbonate bedrock. This valley merges northeastward with the one occupied by the Hudson River and Lake Champlain. Southeast of the Great Valley is tie hilly Piedmont Province. The Piedmont passes northward through the Hudson Highlands and merges with the hilly and mountainous New England Province and with the Taconic Mountains along the eastern New York border.

The basement rocks that make up the Piedmont extend eastward beneath the younger sedimentary layers of the Atlantic Coastal Plain and the continental shelf. Immediately southeast of the Hudson Highlands are the Newark Lowlands. These lowlands formed on layers of sedimentary and volcanic rock of Triassic-Jurassic age. The northeastern end of the Lowlands is bounded by the Palisades, a striking rampart on the west side of the lower Hudson River. Included within the Atlantic Coastal Plain are Long Island, Fishers Island, Block Island, Martha's Vineyard, Nantucket, and Cape Cod.

These are parts of glacial moraines-l orig ridges of clay, sand, gravel, and boulders deposited at the edge of the continental glacier. On Long Island, the Ronkonkoma moraine marks the southernmost advance of the glacier in this region. During the last ice age, the growing mass of ice on the continents depleted the ocean waters enough to lower sea level by 100 meters. As the ice melted, the rising sea made parts of these moraines into islands. Waves and currents have been modifying them ever since.

The continental shelf, slope, and rise lie seaward of the Atlantic Coastal Plain. The continental shelf is nearly level, the continental slope, has a slope of 2-4 degrees; the continental rise slopes less than 1 degree. They are made of material eroded from the land, carried by rivers to the ocean, and distributed there by marine currents. During the period of low sea level, the continental shelf was exposed as part of the coastal plain, and rivers cut valleys across it to the shelf edge.

Most of those valleys have been filled with sediment, but a vestige of the Hudson Shelf Valley still remains. The Hudson Canyon and other, large canyons are cut into the shelf edge and continental slope. Much of this canyon-cutting occurred when rivers, swollen with glacial meltwater and laden with glacial sediment, flowed across the exposed shelf and met the sea at the top of the continental slope. The sediment that the rivers poured into the ocean at those points formed density currents. These currents cut the canyons into the slope.

Bibliography

Grolier multimedia encyclopedia copy right 1996.
Encarta multimedia encyclopedia copy right 1997.