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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
UNIT XII: EROSION, DEPOSITION, AND LANDSCAPES NOTES PACKET
After UNIT XII you should be able to:
o Understand how sediments are transported in a stream, use the Relationship of Transported Particle Size to Water Velocity reference table chart, and recognize the characteristics of sediments that have been weathered in a stream
o Understand basic erosional and depositional features of a river
o Understand the relationship between particle shape and settling rate
o Understand how climate impacts landscapes near rivers
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Picture: The Adirondack Mountains in northern New York State. Most rocks found here are metamorphic in origin and over 1 billion years old. The Grenville Orogeny
NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
o Match topographical features with stream drainage patterns
o Recognize differences between glacial and river sediments
o Recognize differences between valleys eroded by glaciers and rivers
o Recognize common erosional and depositional features of glaciers
o Understand how erosion and deposition function within systems driven by wind, shoreline current, and mass movement and recognize common features of these systems
o Recognize common landscape features of New York State and how they formed
o Be able to use the Generalized Landscape Regions of New York State map
UNIT XII vocabulary you should be able to use and understand:
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 transport of materials on the Earth’s surface in conjunction with your prior knowledge of weathering.
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.
Basic Principles of Erosion
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o Accumulationo Unsorted sedimentso Angularo Continental glaciero Ice sheeto Valley glaciero Alpine glaciero Abrasiono Striationso Polishingo Pluckingo V-shaped valleyo U-shaped valleyo Finger lakeso Drumlinso Erraticso Kettle lakeso Eskerso Kames
o Meander scaro Roundedo Sorted sedimentso Suspended sedimento Settling rateo Deltao Alluvial fano Downcuttingo Stream drainage patterno Orientationo Resistanceo Weatheringo Lowlandso Arido Canyonso Humido Topographyo Glaciero Escarpment
o Erosiono Sedimento Gravityo Velocityo Particleo Transporto Boulderso Cobbleso Sando Silto Clayo Dissolved mineralso Depositiono Diametero Morphologyo Transecto River channelo Meandero Oxbow lake
o Moraineso Outwash plaino Cirqueo Areteo Horno Sand duneso Long-shore drifto Mass movemento Landslideo Slumpo Creepo Mudflowo Mountainso Fault-block mountainso Folded mountainso Landscape regiono Plateauo Plaino Valleys
NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
There are 5 distinct agents of erosion:
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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:
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Describing Rock Particle Size
Rock Particles are categorized into 6 types:
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*Dissolved minerals are also transported, although they are not visible
Sediment Transport Chart
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If water velocity falls below that level, sediment is deposited on the bottom of the river
Using the Chart
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Increasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing SizeIncreasing Size
NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
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Water Velocity and Stream Morphology
Water velocity is not a constant along a river nor is it constant across a transect
In other words, the stream is faster in some areas, slower in others
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
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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.
If the oxbow dries up, it becomes what is known as a meander scar
Sorting of Sediments
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
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
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Shape and Density of Deposited Sediments
When water velocity slows, the shape and density of sediment suspended is important when it comes to the rate that the particles are deposited (settling rate)
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Using Principles of Deposition to Find Gold
You can pan for gold and find it in New York State streams, however a strange law prohibits you from keeping what you find. Most gold in the state was transported by glaciers and ground down into fine dust and then concentrated in streams, although nuggets are found on occasion.
Since gold is high in density, it settles first when water slows. When panning for gold, focus on cracks or joints in bedrock within the stream, and on the inside of meanders.
Rivers Entering Lakes and Oceans
The deposition of sediments at the mouth of a river results in the formation of a delta or alluvial fan
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Stream Valley Shape
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Drainage Patterns
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
Looking at maps and examining rivers often tells us something about the rock strata beneath. Stream drainage patterns are dictated by:
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Differences in Elevation
Higher elevations with steep slopes result in deep ‘V’ shaped valleys
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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.
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Drainage Topography in Humid Regions
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Common occurrence in NYS
Drainage Topography
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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.
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Types of Glaciers
For our purposes, there are 2 types of glaciers that we are concerned with:
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
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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
The glacial movement map (with gray arrows) shows directional flow of the recent surges of ice
Glacial Weathering
Abrasion is the dominant form of weathering underneath a glacier
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This sediment may also result in the polishing of bedrock Glaciers also pluck rock masses in their base and carry them along
Glacial Erosion
As glaciers erode a valley, they leave evidence of having been there
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Finger Lakes
Glacial erosion can leave behind a variety of observable features
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Satellite image (right) of the Finger Lakes region of New York State and the inferred glacial movement that produced them (left)
Drumlins
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
Elongated hills called drumlins are also found in areas that have undergone glaciation. The steeper end is on the side where the glacier approached, the tapered end is the side the glacier was moving.
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Our Chimney Bluffs field trip was to one of the thousands of drumlins found in central and western New York (image shows high lake level after glacial melt)
Erratics
Very large boulders that do not match local bedrock type (transported) or are found in awkward elevations or places were likely transported there by a glacier.
This erratic is in Central Park sitting on top of striated bedrock, another piece of evidence for glaciation.
Kettle Lakes
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Devil’s Bathtub in Mendon Ponds Park is a kettle lake, one of a few that can be found there
Eskers
Long, winding hills of sediment deposited by streams beneath a glacier
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
Kames
Rocky debris that is deposited in crevasses within a glacier to form a hill. A kame in Mendon Ponds Park is the highest point in Monroe County.
Kames, eskers, and kettles can all be found in Mendon Ponds Park.
Moraines
Moraines are long hills that are composed of material that a glacier has pushed or pulled along
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The Valley Heads Moraine in the Finger Lakes Region represents the extent of the last glacial advance and prevents southward drainage of the lakes
The Pinnacle Hills Range in Rochester – A series of hills caused by a sudden resurgence of ice depositing sediment and home to many radio and telecommunication towers
Outwash Plain
An outwash plain is where streams 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 (such as the Adirondack region) 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
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
Wind Deposition
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Wave Erosion and Weathering
Abrasion is the dominant form of weathering along beaches
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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.
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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
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Slump
Blocks of land that have tilted and moved downhill along a surface that curves into the slope
Mudslides/Flows
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
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
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Mountains
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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
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NYS Example: Allegheny Plateau
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NYS Regents Earth Science UNIT XII: Erosion, Deposition, and Landscapes
Plains
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Example: Erie-Ontario Lowlands, City of Rochester
Valleys
Valleys can be formed from erosion by rivers, glaciers, in between folds in bedrock, or where a fault block has fallen down.
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Ridges
A chain of mountains or hills that form a crest for some distance
Folded bedrock in Pennsylvania has formed ridges along the folds
Ridges are sometimes lines of resistant bedrock
Escarpments
Escarpments are long cliffs formed by erosion or faulting
Land is relatively flat on either side
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NYS Landscape Map
Use this map to identify major landscape regions in NYS
For example: Which landscape region is Rochester located in?
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