Landscapes

A landscape is the shape of Earth's surface in a region, including its hills, valleys, ridges, and flats. Weathering, erosion, and deposition are what shape it. Geologists describe a landscape using a few characteristics they can measure.

Elevation is height above sea level. Relief is the difference in elevation between the highest and lowest points in an area, so it measures how rugged the land is. A flat plain has low relief even when it sits at high elevation. A place with tall peaks next to deep valleys has high relief. Slope is the steepness of the land. The stream drainage pattern is the shape the rivers make as they cut across it. Together these tell you what kind of landscape you are in, and they hint at the rock beneath your feet.

A landscape region is an area where the landscape characteristics are roughly the same throughout, because the bedrock and its structure are roughly the same. The moment the underlying rock changes, the landscape usually changes with it, so the boundaries between regions are often sharp rather than gradual. Cross one and the hills, the soil, and the drainage can all shift at once.

That link between rock and surface is the key idea of the unit. The landscape tells you about the geology below. Three broad kinds of region cover almost everything, and you tell them apart by two things, the elevation and the structure of the bedrock.

Mountains have high relief and bedrock that has been distorted. The rock has been folded, faulted, or tilted, so the layers are no longer horizontal. That distortion is the giveaway. The Adirondacks are a domed mass of ancient rock pushed up into the highest peaks in New York.

Plateaus have high elevation, but their bedrock is still in flat, horizontal layers. Streams cut down into that raised rock and shape it into hills and valleys. That is why a plateau can look rugged even though the rock underneath was never disturbed. Most of southern New York is the Allegheny Plateau, and the Catskills are its most deeply eroded part.

Plains, also called lowlands, have low elevation and low relief, with horizontal bedrock or loose sediment. They are the flat, gentle country. New York's lowlands run along the Great Lakes, up the Hudson and Mohawk valleys, and out to the Atlantic Coastal Plain that forms Long Island.

Two regions with the same rock can still look different if their climates differ, because climate controls which kind of weathering dominates. In a humid climate, plenty of water drives chemical weathering and grows thick vegetation, so hillsides round off and slopes are gentle, gradual, and soil-covered. New York is a humid landscape, all rounded hills and green valleys.

In an arid climate, there is little water for chemical weathering and little plant cover to hold soil in place. Mechanical weathering dominates, so slopes stay steep and angular, with sharp ridges and bare rock. The same layer of rock that makes a gentle green ridge in New York would stand as a hard-edged cliff in the desert.

The pattern a river system makes when you look straight down on it is another readout of the bedrock. Three patterns come up again and again.

A dendritic pattern branches like a tree, with tributaries joining at all angles. It forms where the bedrock is uniform and flat-lying, so the water has no preferred direction to follow. This is the most common pattern. A radial pattern has streams flowing outward in all directions from a central high point. It tells you there is a dome or an isolated mountain there, like the Adirondacks. A trellis pattern has long parallel main streams with short tributaries joining at right angles. It forms where alternating hard and soft rock layers, tilted or folded, steer the water. Read the pattern and you can work out the structure you cannot see.

Set the elevation, the bedrock structure, and the climate, and see which landscape region you have built and what its slopes would look like. Distorted rock means mountains no matter the elevation. When the rock is horizontal, elevation decides between a plateau and a plain, and climate sets the shape of the slopes.

Every landscape sits between two opposing sets of forces. Uplifting forces, driven by the movement of the crust, raise the land and build relief. Leveling forces, the weathering and erosion you met in Unit 5, wear it back down and carry it to the sea. A landscape is the running result of that contest.

When the two roughly balance, the landscape can hold a steady overall shape for a long time, even though rock is constantly being lifted, broken, and carried away. That steady state is called dynamic equilibrium. Speed up the uplift and mountains grow. Let erosion win and even the tallest range wears down to a plain, given enough time. The Adirondacks are still slowly rising. The ancient Taconics to the east have already been worn low.

New York packs all three region types into one state, which is why the Reference Tables include a map of its landscape regions. Learning them ties the whole unit to home ground.

The Adirondack Mountains are a roughly circular dome of very old metamorphic and igneous rock in the northeast. They are high and rugged, with radial drainage. The Allegheny Plateau is the largest region and spans the Southern Tier. It is flat-lying sedimentary rock, raised up and cut apart by streams, and the Catskills are its most eroded corner. Remember that the Catskills count as a plateau because of their rock, even though they look like mountains. That is a favorite exam trap.

The lowlands ring the higher ground. They include the Erie-Ontario Lowlands along the Great Lakes, the Hudson-Mohawk Lowlands up the river valleys, and the St. Lawrence and Champlain Lowlands to the north. Along the eastern edge, the Taconic Mountains, Hudson Highlands, and Manhattan Prong are older, distorted mountain rock. In the far southeast, the Atlantic Coastal Plain of Long Island and Staten Island is the lowest and youngest region of all. It is built of loose coastal and glacial sediment rather than solid bedrock.

A landscape is the shape of the surface, described by elevation, relief, slope, and drainage, and it tells you about the bedrock below. Landscape regions share characteristics because they share rock, so their boundaries are usually sharp. Mountains have distorted rock and high relief. Plateaus have high but horizontal rock cut by streams. Plains are low and flat. Climate sets the shape of the slopes, which are rounded and gentle in humid New York and steep and angular in dry country. Drainage patterns reveal the structure underneath, whether dendritic, radial, or trellis. Every landscape is a balance between uplift building the land up and weathering and erosion wearing it down.

Ten Regents-style questions, one at a time in a focused view, each with an instant explanation. The set reshuffles when you reach the end, so you can keep practicing as long as you like.