Transcript Weathering and Erosion - Monte Vista School District

Weathering and Erosion
Objectives
 Identify
the cause of rock shaping due to
weathering and erosion
 Explain how chemical weather forms
caves
 Describe how acid rain affects the
landscape
Two Types of Weathering
or Mechanical – breaking rock
into smaller pieces
 Physical
– breaks down the rock into
something else
 Chemical
Ice can break Rocks
 When
water freezes it expands and gets
less dense (this is why ice cubes float)
 Frost Wedging is when water enters a
crack in a rock, freezes and expands, and
pushes the rock apart
 Frost wedging is why there are more rocks
on the roads next to cliffs after winter
months
Example of Frost Wedging

Frost
wedging
has broken
the rock
into layers
and
pushed
them in
many
directions
Plant roots break rocks
 Plant
roots enter a crack when they are
small
 As they grow, they expand and crack the
rock
Bryce Canyon National Park
HooDoos Form In Bryce Canyon
 The
HooDoos form from a combination of
Frost Wedging and Chemical Weathering
 200 days a year, the temperature in Bryce
Canyon fluctuates both above freezing
and below freezing
 That’s 200 days a year for frost wedging to
occur
 The chemical weathering is both oxygen
and acid rain
HooDoos in Bryce Canyon
Arches National Park
 Arches
also form from Frost Wedging,
wind erosion, and Chemical Weathering
Fins form when cracks in
sandstone are eroded
Double Arch has been used in
movies (Raiders of the Lost Arc)
Weathering continues on fins,
some fins collapse, others form
spires and arches
Glaciers also erode rocks
 Glaciers
are large rivers of ice
 They flow, slowly, down slopes
 As they flow, they carve the rocks
underneath them and take large amounts
of rocks and boulders with them as they
move
 They also grind some of the rocks into
small particles called Glacial Silt
Yosemite Valley
Glacial Silt

Glacial silt is common
in Alaska and
extremely dangerous
 Tourists walk out onto
the beaches of
Alaska, only to realize
it is like quicksand
 They get stuck and
the tide comes in
Glacial Silt

The murky
looking
water is
caused by
fine Glacial
silt floating
in the water
Lake Louise, Canada
The water color is from Glacial Silt
Yosemite Valley
 Yosemite
is formed from mostly Granite
 Granite takes longer to erode than the
sandstone of Bryce Canyon and Arches
National Park
 The major shapes in Yosemite were
weathered by Glaciers moving through the
valley
 Frost Wedging does still occur today
Half Dome was cut by a Glacier
Chemical Weathering
 Things
as basic as Oxygen, Carbon
Dioxide, and acid cause chemical changes
in rocks
Oxidation
 Oxygen
is a very reactive element
 Oxygen combines with many elements
 The Red Rocks seen around the Rocky
Mountains (Grand Junction, New Mexico..)
are Hematite
 Hematite forms when iron reacts with
oxygen
 The red color is an indication of old rocks
and old soils
Grand Junction, Colorado
Chemical Weathering
by Carbon Dioxide
 Carbon
Dioxide gets dissolved in rainwater
 Carbonic Acid, H2CO3
 Although this is a weak acid, it is strong
enough to weather rocks both above
ground (acid rain) and below ground
(caves)
Cave Formations
 We
talked about cave formation yesterday
 Caves are usually in limestone
 Limestone reacts with Carbonic Acid in the
water and “dissolves” and is carried away
pH measures acid





Neutral water has a pH of 7.0 and has the same
amount of hydrogen ions (H+) as hydroxide ions
(OH-)
Hydrogen ions are acidic
Hydroxide ions are basic
Many things you drink are acidic (they can cause
damage to your insides) like Coffee, Soft drinks,
Orange Juice
Milk is a basic drink (does not cause damage)
Acids
 Numbers
below 7 are acidic
 Lower numbers are more acidic
 Coffee and many soft drinks have pHs
around 2-3, they are very acidic, they eat
the enamel of you teeth
Bases
 pHs
above 7 are considered Bases
 These do not have the reactive hydrogen
ions in them and do not cause damage
like acids do
 There is research that indicated many
diseases could be prevented or reversed if
our bodies pH were kept more basic, this
includes cancer and many viruses
Mountain Dew Mouth
It’s acidic dude
 This person is 15!

Acid Rain
 Rain
water is naturally acidic in many parts
of the country
 Rain water below a pH of 5.7 is acidic
enough to damage forests, streams, living
organisms, and rocks
 Because humans continue to burn fossil
fuel, our rain is becoming more acidic
 Fossil fuel increases the amount of Nitrous
acid and sulfuric acid in our rain water
Coal Fired plants release
nitrogen and sulfur dioxide
Effect of acid rain on forests
Effect of acid rain on statues
These are not old statues
Erosion
 Erosion
is the removal and transport of
weathered and non-weathered material
 Can be from running water, wind, waves,
ice, gravity
 Water is the most effective agent of
weathering and erosion (we’ve already
discussed glaciers, cave formation, acid
rain)
Streams move more than water
 Have
you seen the Rio Grande in Spring?
 It’s muddy, it’s carrying with it soil, rock,
and organic material (leaves, branches,
dead animals…)
 Streams can carry material when they are
moving fast
 When water slows down, it drops much of
what it was carrying
Deposition
 Sediment
is laid
down
Rocky Mountain National Park
Water flowing down steep hill
slowed and deposited mud
Ocean’s move sediments
 Wave
action - Ocean waves can erode
coastline. In many areas where people
own coastline, they can lose property to
the ocean.
 You can lose 40 feet in one storm
The coastline is eroding
Erosion removes sand from beaches

Waves erode beaches
 Miami Beach is losing beachfront property every
year
 Cape Cod, Mass. Also loses beachfront property
– some people have to move their houses so the
house is protected from the eroding coastline
Things
communities do
to save their
beaches
 Build
retaining walls
 Bull dose more sand in
to beaches