Download Morphology (-Plate Tectonics)

Morphology – Forming & Reshaping Physical Regions over Time
Objectives:
1. Define morphology.
2. List and explain the major forces – weathering, erosion, glaciation, plate tectonics, deposition – that create and
reshape existing physical features and regions.
3. Diagram the forces of weathering, erosion, glaciations, plate tectonics, and deposition.
4. Provide or choose examples of weathering, erosion, glaciation, plate tectonics, and deposition.
Few major forces create physical regions
1. Weathering and erosion
2. Plate tectonics
3. Glaciation (a special type of erosion and deposition)
4. Deposition
Much of landscape creation, regardless of the force, is driven by
1. The water cycle – weathering, erosion, deposition
2. Gravity
3. The sun
4. Winds
1. Plate tectonics
Definition: a theory that states the earth’s crust is broken into several large pieces,
referred to as plates, that move as a result of convection currents in the earth’s mantle. The
movement of these plates can explain earthquakes, volcanism, mountain/hill formation, trench
formation, ridge formation, and valley formation.
Three types of boundaries, known as faults, exist between plates
i.
Transform: plates rub against one another
i. Causes earthquakes – San Andreas Fault, California
ii. Causes tears in the crust (and roads, apparently)
ii.
Convergent: plates are pushing towards one another
i. Above water this creates mountains – Himalayas, Andes
ii. Below water this creates subduction zones: one plate is pushed below
1. massive trenches form – Mariana Trench
iii. Divergent: plates are moving apart from one another
i. Above water this creates volcanoes and valleys – Great Rift Valley
ii. Below water this creates ridges and volcanoes – Mid-Atlantic Ridge
Evidence to support plate tectonics
1. Continents fit together <SHOW PANGEA VIDEO>
a.
Known as Pangea -> Laurasia/Gondwanaland -> modern continents
2. Fossils at the edge of what would have been connected lands are similar
3. Areas of seismic activity follow certain boundaries (believed to be plate boundaries) <SHOW SEISMIC BOUNDARIES IMAGE>
4. we observe changes to the earth at plate boundaries – mountains, trenches, ridges, etc <SHOW SEAFLOOR SPREADING>
5. Sea floor aging shows that the seafloor closer to the continents is older, younger at the mid ocean ridges where plates separate
<SHOW SEAFLOOR AGE IMAGE>
6. Alternating polarity bands in minerals found at areas of spreading seafloor
a.
Earth occasionally switches its poles (est. 200,000 years)
b. Any newly created magnetically affected mineral (such as iron) will align its molecules with reference to the changing poles
c.
As the floor spreads, alternating bands of polarity form <SEE IMAGE>
2. Weathering and erosion
Weathering – changes made to the lithosphere that do not involve movement
A. Chemical – breakdown of rocks into different minerals or compounds
THINK: burning a piece of paper
1. Oxidation – interaction of oxygen with metallic minerals
Ex. Rust
2. Hydration – water causing reactions with chemicals in minerals
3. Carbonation – carbon dioxide interacting with chemicals in minerals
4. Dissolution (dissolving) caused by compounds in the air/water
Ex. Acid rain
B. Physical/mechanical – breakdown of rocks into smaller pieces of same mineral
THINK: ripping a piece of paper into smaller pieces
1. Thermal expansion
a. Cyclical temps from very high to very low
b. Top layer of rocks “peel” off like an onion
2. Frost wedging / shattering
a. Water enters a crack or uneven part of a rock surface
b. Water freezes, causing it to expand, and cracks a rock
3. Salt crystal growth
a. Salt water enters a crack or uneven part of a rock surface
b. Water washes out, leaving behind salt crystals
c. Crystals heat up, causing them to expand, and cracks a rock
Erosion – changes made to the lithosphere that involve movement, often due to gravity
1. Tumbling down a sloped plain - scree / talus
2. Water erosion –
a. splash (Rain)
b. valley (stream)
c. wave pounding (waves)
3. Air erosion – abrasion (wind blasting)
4. Ice erosion – abrasion (scouring bottom of glacier)
3. Glaciation (technically it is a type of erosion at times and deposition at others)
Definition: the establishment and growth of ice sheets due to the build up of excess snow
and ice that does not have time to melt or thaw in the summer months. Ice sheets expand
during ice ages, which are thought to be caused by wobbles in the earth’s tilt over huge
periods of time, and recede during periods between ice ages (interglacial periods).
Glaciers have many impacts on the landscape from around 45 degrees N and up
tilling: dropping of heterogeneous (mixed) rocks over an area
just dig in your back yard
erratics: large rocks that do not match the surrounding rocks
you can see this across the road
moraines: a collection of glacial debris, it can be in a valley or it can be across the
land, in which case it looks like rolling hills
Fast Fact: Long Island is composed mostly of two glacial moraines
drumlins: small hills that are formed parallel to a glacier face either as it melts (thus
pushing rocks and sediment together) or as it expands (pushes sediment up and out of
the way)
scouring: scraping or gouging of rocks by friction of advancing glacier/ice sheet
valley cutting/gorging/fjords: friction of expanding ice sheet cuts into softer rock
Fast Fact: advancing glaciers cut Niagara Falls out of a soft limestone bed
lakes: receding ice sheets/glaciers melt during interglacial period and deposit large
quantities of water in the gouged areas.
Fast Fact: The Great Lakes and the Land o’ Lakes are glacial lakes
4. Deposition
Definition: when all the sediments and broken rocks from weathering, erosion, plate tectonics,
and glaciations are dropped in new locations and settle. This is the final step in recreation of
landscapes.
Glacial deposits
i.
Sharp, jagged shapes
ii. Generally strewn about or in large piles
Erosion deposits
i.
Smoother shapes
ii. Settle into layers – larger sediment on bottom, smaller sediment on top
iii. Generally at the end of streams and rivers or in areas of runoff