Tying it together… You now have had significant experience learning about the variety of ways rocks form, and some unique formations associated with the study of plate tectonics. You are most familiar with what are known as uplifting forces. For example, the contribution of plate convergence to volcanic mountain ranges. New crust is formed, old crust is recycled back into the Earth. The focus of this unit seeks to broaden your understanding of leveling forces, those which contribute to wearing away of materials on the Earth’s surface.

Our weathering unit taught us that rocks can be broken down by both physical and chemical means based on climate and bedrock type. Understanding how Earth materials erode, becomes the next step in truly understanding the dynamic nature of landscapes. What is erosion?  Erosion is the removal of rock particles and soil from an area  Erosion requires energy to take place  Erosion is driven by gravity

There are 5 distinct agents of erosion:  Rivers/streams  Glaciers  Wind  Wave Action  Mass Movement

Erosion in moving water varies greatly within a river, and between rivers. Lighter, less dense sediment is first to be transported by moving water.

Transport of Sediments in Streams Sediment transport is dependent on 2 variables:  Velocity (speed) of water  Particle size and shape

Describing Rock Particle Size Rock Particles are categorized into 6 types:  Boulders  Cobbles  Pebbles  Sand  Silt  Clay *Dissolved minerals are also transported, although they are not visible Increasing Size

Quantified Sediment Sizes

Sediment Transport Chart  In general, the chart shows that larger particles require an increased water velocity (speed) to be transported  If water velocity falls below that level, sediment is deposited on the bottom of the river

Using the Chart  The chart shows average particle diameter (particle classification) and the velocity required to maintain movement of that particle in moving water

Water Velocity and Stream Morphology  Water velocity is not a constant along a river nor is it constant across a transect

Water Velocity and Stream Morphology Water, for the most part, flows in a straight line and will do so until redirected by the stream channel. Water also over time dictates how the channel changes.  Because this is true, rivers have different channel shapes at different locations  In a straight line path, rivers are fastest in the middle, leaving a channel deepest in the center  As river water enters a curve, the faster water is on the outside causing more erosion and a greater depth  Water slows on the inside of a curve, causing deposition of particles

Stream Meanders Over time, erosion at the outside of the bend causes the stream channel to drift. When the old channel is cut off, an oxbow lake is formed.

Sorting of Sediments  Faster moving water transports smaller sediments  Therefore, a stream bottom will have larger particles on the bottom in faster moving water and smaller particles on the bottom in slower moving water  Streams deposit rounded, sorted sediments based on water velocity

Rivers Entering Lakes and Oceans The deposition of sediments at the mouth of a river results in the formation of a delta  The stream flow slows resulting in deposition of largest particles first  Particles such as silt and clay are carried away from the mouth until there is no longer sufficient velocity to transport them

Stream Valley Shape  As streams downcut through soil and bedrock, they create a V-shaped valley

Drainage Patterns Looking at maps and examining rivers often tells us something about the rock strata beneath. Stream drainage patterns are dictated by:  Differences in elevation  Characteristics of rock layers (resistance to weathering)  Orientation of rock layers (how the rocks are tilted or folded)

Differences in Elevation Higher elevations with steep slopes result in deep ‘V’ shaped valleys  Level lowlands result in more meanders in the stream

Drainage Topography in Arid Regions Weathering in dry regions is generally a very slow process. The majority of weathering and erosion takes place in the river channel.  Canyons are common because the canyon walls weather very little over time

Drainage Topography in Humid Regions  Gentler slopes are a result of more rapid weathering of rock  Common occurrence in NYS

Drainage Topography  Drainage patterns match the surrounding landscape and are flowing from high to low elevations  Mate these with an overhead pattern

Glaciers New York State owes its many unique landforms to the presence of glaciers in the past. Evidence of repeated glacial events surrounds us in western New York. Glaciers are responsible for both erosional and depositional features.  Glaciers form when repeated snowfall accumulates in an area and forms into an ice pack that is able to flow

Types of Glaciers For our purposes, there are 2 types of glaciers that we are concerned with:  Continental (ice sheet): Spans all or some of a continent  Valley (Alpine): Restricted to a valley

Glacial Presence in NYS  A massive glacier covered New York (most recently around 10,000 years ago), and it is important to understand how it shaped landforms in the area

Glacial Weathering Abrasion is the dominant form of weathering underneath a glacier  Rocks and other sediment are ground against bedrock as they are dragged overhead  Evidence: We find parallel grooves, called striations, in bedrock that indicate the direction of movement

Glacial Erosion As glaciers erode a valley, they leave evidence of having been there  Valleys take on a “U” shape

Finger Lakes Glacial erosion can leave behind a variety of observable features  Finger Lakes are carved out of bedrock in the direction that the glacier moved

Drumlins Elongated hills called drumlins are also found in areas that have undergone glaciation  The drumlins align with the direction of glacial movement

Erratics Large boulders that do not match local bedrock type or are found in awkward elevations or places were likely transported there by a glacier

Eskers Long, winding hills of sediment deposited by streams beneath a glacier  Sediment will be sorted and rounded because it was transported by running water

Kames Rocky debris that is deposited in crevasses within a glacier to form a hill

Kettle Lakes  When large chunks of the glacier break off and are partially buried, they melt to form a kettle lake

Moraines Moraines are long hills that are composed of material that a glacier has pushed or pulled along  Rocks in moraines are unsorted and angular (no abrasion in running water)

Outwash Plain An outwash plain is where many streams (or just a few) flow out of the glacier as it melts. The plain is relatively flat with sorted and rounded sediments due to abrasion in the streams

Cirques, Aretes, Horns All features found in mountainous areas once covered by glaciers Horn: Sharp point at mountain peak Cirque: Bowl-shaped depression caused by abrasion Arete: Sharp ridge carved out of the mountainside

Wind Erosion and Weathering  Abrasion is the dominant form of weathering in dry climates  Rocks become “sand-blasted” and the particles are blown away

Wind Deposition  Sand and other particles are deposited in dunes

Wave Erosion and Weathering Abrasion is the dominant form of weathering along beaches  Particles are washed on shore, swept back out, and gradually move in the direction of the current (long shore drift)

Long Shore Current Long shore currents flow parallel to the beach. This flow steadily drags sediments along the shore in what is called long shore drift.

Mass Movement The final, though less substantial type of erosion is called mass movement.  Mass movement is the sliding of any rock material or soil downhill as a result of gravity  Some mass movement is slow, and some is sudden

Landslide Landslide is a commonly used term for the movement of a mass of bedrock or loose soil and rock down the slope of a hill, mountain or cliff.

Creep  Slow, imperceptible movement of soil down a slope Slump  Blocks of land that have tilted and moved downhill along a surface that curves into the slope

Mudslides/Flows  Rapid movement of Earth saturated with water

Weathering, erosion, deposition, plate tectonics, folding and faulting all contribute to the beautiful landscapes around us, many of which can be found in New York.

Landscapes Features of NYS  Mountains  Plateaus  Plains  Valleys  Ridges  Escarpments

Mountains  Mountains are classified as locations that have a much higher elevation than surrounding areas NYS Example: Mount Marcy (Adirondack Mountains) The Adirondack Mountains are part of an area which has been uplifted and domed upward and continues to do so. They are not volcanic in origin and are comprised mostly of metamorphic and intrusive igneous rocks.

Other Types of Mountains  Folded Mountains form when compression occurs typically during a tectonic collision  Fault Block Mountains occur when faults (lines of breakage) allow rock on either side to move up or down relative to the opposite side

Plateau  A region characterized by a high, flat area  Some may appear to look like mountains after rivers have cut through them NYS Example: Allegheny Plateau

Plains  Generally low-lying, flat area Example: Erie-Ontario Lowlands

Valleys Valleys can be formed from erosion by rivers, glaciers, in between folds in bedrock, or where a fault block has fallen down.  Valleys are conspicuously lower areas of elevation compared to the surrounding landscape

Ridges  A chain of mountains or hills that form a crest for some distance

Escarpments Escarpments are long cliffs formed by erosion or faulting  Land is relatively flat on either side  Niagara Escarpment is caused by differential weathering of bedrock

NYS Landscape Map Use this map to identify major landscape regions in NYS For example: Which landscape region is Rochester located in? Answer:__________________________