how the rocks are tilted or folded

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:
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
Transport of Sediments in Streams
Sediment transport is dependent on 2 variables:
 Velocity (speed) of water
 Particle size and shape
Describing Rock Particle Size
Increasing Size
Rock Particles are categorized into 6 types:
*Dissolved minerals are also transported,
although they are not visible
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
 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
 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
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
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
 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
Elongated hills called drumlins are also
found in areas that have undergone
 The drumlins align with the
direction of glacial movement
Large boulders that do not match local
bedrock type or are found in awkward
elevations or places were likely
transported there by a glacier
Long, winding hills of sediment
deposited by streams beneath a
 Sediment will be sorted and
rounded because it was
transported by running water
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 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
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
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 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.
 Slow, imperceptible movement of
soil down a slope
 Blocks of land that have tilted and
moved downhill along a surface
that curves into the slope
 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 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
 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
 Generally low-lying, flat area
Example: Erie-Ontario Lowlands
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
 A chain of mountains or hills that
form a crest for some distance
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?