Transcript 4th Grade Rockin` Science

Grade 4
Rockin’ Science
Key Information for Lesson on Erosion & Weathering
Erosion Terminology
"Erosion and sedimentation are complimentary geological processes."
• Erosion
•
the wearing away of rock materials and removal from one
area of the Earth’s surface. Erosion tends to occur in two
forms:
•
Earth processes which move material on the Earth’s surface
over long periods of time, such as weathering and gravity
•
Human activity which moves material on the Earth's surface
over short periods of time, such as residential and
commercial development, farming, etc., that results in the
alteration of the landscape and surrounding animal
communities
• Sedimentation
• is the act or process of depositing sediments which have
usually been transported for some time and distance.
Sedimentation is caused when something carrying the
sediment has to deposit it in an area and the sediment
begins to accumulate. Examples include when gravity
causes sediments to move down the slope of a mountain
or hill and they are deposited at the base of the slope;
when sediments carried by wind or water are released
because these currents are slowed and lack the force to
continue moving them; when glaciers melt and the
carried sediments are deposited in one area; or when
materials that have dissolved in water are left behind as
the water is evaporated.
• Soil
• is the thin and loosely packed layer
• Rills
• are cuts made in the soil due to the
of earth materials composed of
decaying organic matter and
weathered minerals which provides
nutrients, physical support, and
adequate amounts of air and water
for plant growth.
action of flowing water as it picks
up sediments in the soil. Over time,
rills may grow to become gullies,
creekbeds, rivers, the Grand
Canyon, etc.
Forces which drive erosion include:
• physical forces (also known as mechanical
forces) such as wind, flowing water,
flooding, gravity, temperature shifts
(expansion and contraction),
evaporation due to the sun, and
glacial ice melts
• chemical forces such as acid rain acting
upon exposed rock and forest fires
which remove plants anchoring the
soil
• biological forces such as beavers who
dam rivers and flood land areas and
people whose human practices
expose soil
• biochemical forces such as acids
deposited by plant roots or fallen
leaves or by animal waste such as
urine. Both can lower the pH of the
soil making it difficult for protective
plant growth to occur
What are the types of erosion?
•
Subaerial erosion describes erosion that occurs when
land is exposed to the atmosphere. Chemical or
mechanical processes alter exposed rock (weathering)
which is then transported in a variety of ways. The
leading causes of subaerial erosion include gravity,
running water, ice (often in the form of glaciation),
wind, and nearshore ocean waves.
•
Gravity erosion (also known as mass wasting)
occurs where slopes and other irregularities in land
surface allow gravity to weather away and transport
rock debris downward. Crystal movements, also
known as diastrophism, commonly cause slope
formation, along with valley cutting by streams. This
process of downhill creep of rock debris may be
accelerated by the effects of running water but
generally is so gradual that it is imperceptible.
•
Running water (fluvial) erosion is when the force
of moving water dislodges rocks and other solid
particles which are carried along by the water. These
particles scrape and scour the soil, loosening it and
carrying it away. This scouring caused by the bouncing
and rolling of solid particles is called saltation.
•
Ice or Glacial erosion occurs when glacial ice freezes
to rock particles and the rocks are then pulled loose
and become stuck to the glacier. The rocks are then
carried along, scraping and eroding the Earth’s surface
as the glacier moves.
What are the types of erosion
• Wind (Eolian) erosion is most destructive in
areas where there is little to no ground cover
and small rocks, sand, and silt are blown across
the land. Deflation is the process by which rocks
are picked up and moved by wind.
• Wave erosion is caused by the recurring crash
of waves along coasts and beaches. The impact
of the waves and the sediment that is carried in
erode the shoreline.
• Subaqueous erosion is when currents move
along the bottom of bodies of standing water
and the currents move solid fragments of
rock/soil which, in turn, scrape the soil layer
and cause soil loss in the area.
•
•
•
•
•
•
•
1. Subaerial
2.Gravity
3. Ice or Glacial
4. Running water (fluvial) erosion
5.Wind
6. Waves
7. Subaqueous
What is the effect of erosion on the
environment?
• Sedimentation in rivers
• Removal of topsoil from land areas
• pollutes water with soil particles
• damages water ecosystems through
• prevents plant growth
• alters ecosystems, thus reducing the
• increases water treatment costs for
• destroys crops
• reduces agricultural food production
• reduces farming income
reduced sunlight for aquatic plants
and animals
human water consumption
• reduces the depth of rivers, thus
creating waterways that can't be
navigated by commercial crafts
biodiversity of life
What is the effect of erosion on the
environment?
• Wind erosion
• increases the amount of particles in
the air
• reduces visibility
• reduces air quality
• causes breathing problems (asthma,
etc.)
• Misconception(s). Misconception:
Students tend to think of natural
geologic erosion as being as largescale and fast-paced as the types of
erosion which occur due to human
activity. Fact: Natural geologic
erosion is a very slow, small-scale
form of erosion.
Lesson Goal
• Students will propose plans to
correct erosion problems on their
school grounds that may lead to
implementation
• Students will learn about the
different types of erosion and
further develop their observation
skills and group teamwork.