Download constructive__destructive_forces ppt

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
-Delta
-Faults
-Sand Dunes
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
- Glaciers
– Weathering/Erosion - Landslides
– Volcanoes
- Tsunami
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
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
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
Stalactites & Stalagmites
created by acid rain falling
into these limestone
caverns.
Stalactites
Stalagmites
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
Technology and
Human Interventions
• Humans try to CONTROL these forces.
– seismological studies
– flood control (dams, levees, storm drain
management, etc.)
– beach reclamation (Georgia coastal islands)
Seismological Studies
• Scientists study earthquakes so that they can
understand how they work and so that they can try to
predict future quakes.
• Earthquakes are recorded by instruments called
“seismographs”.
• A short wiggly line means a small earthquake and a
large one means a large earthquake.
Flood Control
• The U.S. Army Corps
of Engineers began
constructing dams in
Georgia for navigation
and flood control in the
1940s and 1950s under
the Flood Control Act of
1944 and the
Watershed Protection
and Flood Prevention
Act of 1954.
Flood Control Methods
• Dams control the water
flow in a stream or river.
• A levee is an
embankment designed to
prevent the flooding of a
river.
• Storm drains are for
carrying off rainfall
drained from paved
surfaces, roofs, etc.
Beach Reclamation
• Weather, waves and wind cause the
coastline to wash away.
• Keeping sand dunes intact helps to keep
the beaches from eroding.