Transcript Weathering & Erosion - Somers Public School District

Weathering & Erosion
What is weathering?
Weathering is a set of physical,
chemical and biological
processes that change the
physical and chemical properties
of rocks and soil at or near the
earth's surface.
More about weathering

Definition – the breakdown of rock to
form sediment [very small pieces of
rock]
Weathering happens to rocks that are
NOT MOVING
 Weathering is part of the Rock Cycle

There are three types of
weathering
Mechanical [sometimes called physical]
 Chemical
 Biological

Mechanical weathering breaks rocks
down into smaller pieces.
Types of mechanical weathering include
frost wedging, exfoliation, and thermal
expansion.
Chemical weathering breaks rocks down
chemically adding or removing chemical
elements, and changes them into other
materials.
Chemical weathering consists of chemical
reactions, most of which involve water.
Biological weathering is the breakdown
of rock caused by the action of living
organisms, including plants, burrowing
animals, and lichens.
A lichen is a combination of fungus and algae,
living together in a symbiotic relationship.
Lichens can live on bare rock, and they break
down rocks by secreting acids and other
chemicals.
Let’s investigate
mechanical weathering first.
In mechanical weathering, a rock is
broken down into smaller pieces
without changing its mineral
composition.
There are several different processes
that cause mechanical weathering.
View Website
Observe the effects of
mechanical weathering
View Website
View Website 2
Website 3
Enchanted rock
is a huge
example of
exfoliation
mechanical
weathering.
Discuss with your partner how
exfoliation, abrasion and
thermal expansion are
examples of mechanical
weathering
Now, let’s look at
chemical weathering.
In chemical weathering, a rock
is broken down by chemical
reactions that change its
mineral composition and
physical and chemical
properties
Chemical weathering happens
when the minerals that make up
a rock are changed, leading to
the disintegration of the rock
Chemical weathering happens
quickly in warm, moist
environments because water is
needed for the chemical
reactions.
The warm weather speeds up the
reactions.
Not all minerals are prone to chemical
weathering. For example, feldspar
and quartz, are common minerals in
the rock granite, have very different
levels of resistance to chemical
weathering.
Quartz doesn’t weather very easily,
but feldspar does. Over a long time,
it chemically changes into clay
minerals.
View the following websites to
learn more about chemical
weathering


1.) Feldspar to clay
2.) Examples of more
chemical weathering
Biological weathering involves
processes that can be either
chemical or physical in nature.
Biological weathering can be
considered special types of
mechanical or chemical
weathering.
Biological weathering – What is it?
Some biological weathering
processes are:



1. Rocks can break because of animal
burrowing.
2. Tree roots grow into cracks and widen
them, which helps physical weathering.
3. Bacteria, lichens and other organisms
secrete acidic solutions, which helps
chemical weathering.
Lichens on
rocks cause
biological
weathering by
secreting an
acid that
breaks down
the rock.
Plants growing in rocks break the
rocks apart.
Now let’s move on to
EROSION
What is erosion?
Erosion is defined as the removal and
movement of earth materials by
natural agents.
Some of these agents include glaciers,
wind, water, earthquakes, volcanoes,
tornadoes, hurricanes, mud flows,
and avalanches.
How are erosion & weathering
different?
Weathering involves two
processes
[mechanical, chemical]
that often work together to break
down rocks. Both processes
occur in place. No movement is
involved in weathering.
As soon as a rock particle (loosened
by one of the two weathering
processes) moves, we call it
erosion or mass wasting.
Mass wasting is simply movement
down slope due to gravity.
Rock falls, slumps, and debris flows
are all examples of mass wasting.
We call it erosion if the rock particle
is moved by some flowing agent
such as air, water or ice.
In a nutshell: if a particle is
loosened, chemically or
mechanically, but stays
put, we call it weathering.
Once the particle starts moving,
we call it erosion.
What are the different types of
erosion?
View the website to find out.
Water is the most important
erosional agent and erodes
most often as running water in
streams or rivers.
Water in all its forms is erosional.
Raindrops create splash erosion
that moves tiny particles of soil.
Water collecting on the surface of the
soil collects as it moves towards tiny
streams and creates sheet erosion.
Observe river erosion causing
waterfalls
Visit this website
Erosion by wind is known as
aeolian erosion (named after
Aeolus, the Greek god of winds)
and usually occurs in deserts.
Aeolian erosion of sand in the
desert is partially responsible for
the formation of sand dunes.
Painted Desert National Monument
The erosive power of moving ice is
actually a greater than the
power of water. however since
water is much more common, it
is responsible for a greater
amount of erosion on the earth's
surface.
Glaciers cause erosion two ways they pluck and abrade. Plucking
takes place by water entering cracks
under the glacier, freezing, and
breaking off pieces of rock that are
then moved by the glacier. Abrasion
cuts into the rock under the glacier,
scooping rock up like a bulldozer
and smoothing and polishing the
rock surface.
Athabasca Glacier - Jasper, Canada
Waves in oceans and other large
bodies of water cause coastal
erosion.
The power of ocean waves is
awesome; large storm waves can
produce 2000 pounds of pressure
per square foot. The pure energy
of waves along with the chemical
content of the water is what
erodes the rock of the coastline.
Wave action in Calvert County Maryland
Watch wave erosion on this
website
Observe landscapes formed by
erosion click on the website
Let’s look at some more
examples of erosion.
Website
Explore the formation of the Grand
Canyon
Review weathering & erosion
vocabulary with online flashcards.
http://www.studystack.com/javastudysta/frames.jsp
Note: Some of the terms on the cards
have not been covered during this
lesson. Read them anyway; it never
hurts to expand your vocabulary!
The End!
Double check your answers & turn
them in!
Unless otherwise noted, the
source for all photographs in
this presentation is