Constructive Processes

CONSTRUCTIVE PROCESSES
Constructive processes build Earth’s surface up.
These processes build up mountains and carve out
valleys. They create many other kinds of landforms.
CONSTRUCTIVE PROCESSES
Volcanoes
Deposition
Earthquakes
DEPOSITION
Weathering breaks rock down into smaller pieces.
Then erosion moves pieces of rock to new places.
Wind and water carry the rock particles along. But
when wind and flowing water slow down, they cannot
carry as much material. They drop some or all of the
rock particles they are carrying. Deposition is the dropping of material by water, wind,
or glaciers.
DEPOSITION - DELTA
The moving water in a river
slows near its mouth - the
place where the river flows
into the ocean or a lake. As
the river slows, sand and soil
in the water settle to the
bottom. This sediment can
build up and form a flat piece
of land called a delta. A delta is usually shaped like
a triangle or fan.
Mississippi River Delta
DISCUSSION QUESTION
How do weathering, erosion, and deposition combine
to form a river delta?
DEPOSITION - FLOODPLAIN
When rainfall is very heavy, a river may overflow its
banks. Then water spreads out over the land on both
sides of the river. The river slows down and drops
the sediment it is carrying. The sediment forms a
wide, flat area called a floodplain.
FLOODPLAIN
The Mississippi River flows along most of the western
border of Mississippi. North of Vicksburg, there is a
wide floodplain between the Mississippi River and the
Yazoo River. The average width of the floodplain is 65
miles.
DEPOSITION OF RIVER SEDIMENTS
DEPOSITION - BEACH
Ocean water deposits sediment.
Beaches are the main feature formed
on the shore. Much of the sand on
beaches starts far inland. Rivers may
carry it to the ocean, where it sinks
to the bottom. But ocean waves
wash some sand back on shore.
Over thousands of years, beaches
form.
DEPOSITION DUNE
A dune is a hill of sand deposited by wind. Dunes form along some ocean shores and in sandy
deserts. Wind picks up grains of sand, but even a
strong wind cannot carry sand very far. Wind blowing
from the ocean toward land picks up sand along the
shore and deposits it nearby. Sand dropped by wind
starts to build up around rocks or plants on the
shore. As the wind deposits more sand, dunes form.
DUNES
DEPOSITION GLACIERS
Glaciers also deposit sediment. Recall that a glacier is
a huge sheet of ice that moves slowly over land. As it
moves, a glacier picks up rock and soil. When the
glacier melts, it leaves this material behind. A moraine is a ridge of rock and soil deposited when
a glacier melts.
MORAINE
EARTHQUAKES
Earthquakes are destructive and can open wide
cracks in the earth’s surface. But earthquakes can
also build up areas of land.
Most earthquakes happen when rock moves suddenly
along a fault. A fault is a break in the rock that makes
up earth’s crust. Pressure deep underground may
push the land on one side of a fault upward. The
result is a clifflike landform called a fault scarp.
FAULT ANIMATIONS
http://earthquake.usgs.gov/learn/animations/
animation.php?flash_title=Normal
+Fault&flash_file=normalfault&flash_width=22
0&flash_height=320
http://earthquake.usgs.gov/learn/
animations/animation.php?
flash_title=Thrust
+Fault&flash_file=thrustfault&flash_width
=220&flash_height=320
SAN ANDREAS FAULT
http://www.exploratorium.edu/faultline/
http://www2.jpl.nasa.gov/srtm/images/
movies/san-andreas1.mov
EARTHQUAKES
Changes during an earthquake are fast. Rock can also
move at faults much more slowly. Over millions of
years, rock pushed up along faults can form tall
mountain ranges. The Sierra Nevada Mountains in
California formed in that way.
VOLCANOES
Volcanic eruptions also build up earth’s surface.
When a volcano erupts hot, melted rock flows out of
it. That melted rock underground is called magma.
When it reaches the surface, it is called lava. On the
surface, lava cools and hardens. It forms solid rock.
As a volcano erupts over and over, the rock formed
from lava piles up. Over a long time, it can form a
mountain.
Volcano Eruption Animation: http://www.10news.com/
weather/15844616/detail.html
LAVA VIDEO CLIPS
http://www.10news.com/weather/15844616/
detail.html
MOUNT ST. HELENS
VOLCANO CAMS
http://www.fs.fed.us/gpnf/volcanocams/msh/
VOLCANOES
VOLCANOES
The islands that make up the state of Hawaii are
mountains that formed around volcanoes on the
ocean floor. Lava flowing from the volcanoes built up
the mountains until they stuck out of the water.
Some of the Hawaiian islands are still becoming larger,
as the volcanoes continue to erupt.
Formation of the Hawaiian Islands: http://
library.thinkquest.org/J003007/Disasters2/volcano/
formed/formed.htm
EARTHQUAKES AND VOLCANOES
DISCUSSION QUESTIONS
What are some similarities between constructive and
destructive processes?
What are some differences between constructive and
destructive processes?
HOW MOUNTAINS ARE
FORMED
when plates crash together
when plates lift at a fault
volcanic eruptions - magma and lava
erosion - high plateau, rivers carving deep channels
(between river valleys)
HOW V-SHAPED VALLEYS ARE
FORMED
formed by flowing water, normally a river
HOW U-SHAPED VALLEYS ARE
FORMED
formed by glaciers