Constructive &
Destructive
Forces
EQ: What is the
difference between a
Constructive Force and
a Destructive Force?
• Constructive Forces- Natural
forces that build or construct
landforms and cause changes
in the Earth’s surface.
• Examples:
– Volcanoes
– Deposition
– Earthquakes
Constructive Forces
• Constructive forces affect the earth's
surface by building it up to form new
landforms like mountains and islands.
• Examples of these type of forces are:
• Deposition is the dropping off of bits of eroded
rock. This process helps to build up Earth’s
surface by filling in depressions, or basins.
• Earthquakes
• Volcanoes
• Destructive Forces – Natural
forces that destroy landforms
and causes damaging changes
in the Earth’s surface.
- Earthquakes
– Weathering/Erosion
– Volcanoes
Earthquakes:
• Shaking that results from the
movement of rock (tectonic plates)
beneath Earth’s surface
• Destructive force or Constructive
force
• Most occur because of moving
crust
Earthquakes causes vibration across the
ground, sending shock waves that crumble
buildings.
http://jclahr.com/alaska/aeic/taurho/eqeffects/eqtsun.mov
Stress:
• Force that acts on rock to change its
shape and volume
• Energy is stored in the rock until it
breaks or changes shape
3 Types of Stress:
1. Shearing – Pushes rock in
opposite directions
past each other
- Transform boundaries
3 Types of Stress:
2. Tension – Stretches rock so that it
becomes thinner in
the middle
- Diverging boundaries
3 Types of Stress:
3. Compression – Squeezes rock until
it folds or breaks
- Converging
boundaries
Faults:
• Break in Earth’s crust where slabs
of crust slip past each other
• When stress builds up, the rock
breaks along a fault
• Usually occur along plate
boundaries
3 Main Types of Faults:
1. Strike-Slip – Rocks on each side slide
past each other with
little (or no) up & down
motion
- Transform boundaries
- Caused by Shearing
- San Andreas (California)
Measuring Quakes:
• Seismograph –
• instrument used to measure
the vibrations and seismic
waves of earthquakes.
Rating Scales used for Quakes:
2. Richter – Rate quakes according to the
size of the seismic waves
- low ---> high (1-9)
-each # is 10x stronger
- humans cannot feel a quake
below 2
- 6 or more = major quake
- Measures magnitude
Misc. Info:
• Tsunami
• – a series of seismic sea
waves
- result from underwater
earthquakes, landslides,
or volcanic eruptions
Best Way to Protect Yourself:
DROP!!
COVER!!
HOLD!!
Volcanoes:
• Destructive AND Constructive
• Weak spot in the crust where molten
material from the mantle comes to the
surface
• Magma – Hot molten rock located
Below ground.
• Lava – magma that reaches the
surface.
Volcanoes can quickly
change the Earth, too, by
pouring out hot, liquid
rock called lava.
Pahoehoe
Aa
Weathering:
• Process that breaks down rock &
other substances at the Earth’s
surface- very slow process
• Temperature, Water, & gases in the
atmosphere all contribute to
weathering
2 Types of Weathering:
1. Mechanical
2. Chemical
Mechanical Weathering:
• Process by which rock is
physically broken into smaller pieces
• Small pieces have same material as
the original rock
• Very slow occurrence
• The most common type of mechanical
weathering is the constant freezing,
and thawing of water. In liquid form,
water is able to penetrate the many
holes and joints within a rock. As the
temperature drops water freezes and
expands, becoming about 10% larger
than it was in liquid form. The result is
that the holes and cracks in rocks are
pushed outward. Even the strongest
rocks are no match for this force.
Rock split apart by Mechanical
weathering.
Mechanical Weathering:
• Caused by…(Agents)
– Freezing and Thawing
– Release of Pressure
– Growth of Plants
– Abrasion – Grinding away of rock by
other rock particles that are carried
by water, ice, wind, or gravity
Chemical Weathering:
• Breaks down rock through chemical
changes- Chemical properties are
actually changed.
• Rock particles have different mineral
make-up than original rock
Chemical Weathering:
• Caused by…(Agents)
– H2O(Water)  MOST important
– Oxygen (O2)
– Carbon Dioxide (CO2)
– Living organisms
– Acid Rain  very rapid
Stalactites & Stalagmites
created by acid rain falling
into these limestone
caverns.
Stalactites
Stalagmites
Agent
Type
Description
Mechanical Rock particles wear away rock
Chemical
Forms from coal, oil, and gas
burning
Freezing/Thawing
Breaks rock by ice wedging
Carbon Dioxide
Forms carbonic acid in water
Chemical
Weathers marble and limestone
Mechanical Burrowing in the ground breaks rock
Plant growth
Roots pry apart cracks in rock
Living Organisms
Produce weak acid that weathers
rock
Oxygen
Causes rust on some rock
Mechanical Sun or forest fire causes rock to
crack
Erosion:
• Process by which natural forces
move weathered rock & soil from
one place to another (by wind,
water, ice, & gravity)
• Sediment
• Material moved by weathering
and erosion
Mass Movement:
• Deposition
• Caused by gravity
• Occurs where bits of rock are dropped
off (deposited) because of erosion
• On land sediment can be moved down hill
by:
– Landslide
– Mudslide
Landslide:
• Most destructive
• When rock & soil slide quickly down a
steep slope
Mudslide