Rocks and Weathering

Crust/Lithosphere

• Outermost layer of earth

• Continental is thick and less dense as well as being old

• Oceanic is thin and more dense as well as being young

Mantle/Asthenosphere

• A layer of hot melted rock under the lithosphere

Core

• The central part of the earth below the mantle

• Has an inner and an outer

• Inner is denser than outer

Divergent/Constructive Margins/Boundaries

• Plates spreading apart

• As plates move apart new material is erupted to fill in the gap

• 2 oceanic plates results in sea floor spreading and forms mid-ocean ridges

• 2 continental plates results in volcanoes

Convergent/Destructive Margins/Boundaries

• Plates colliding together

• May form mountains, trenches, and volcanoes

• There are three styles

  • Continent-continent

  • Continent-oceanic

  • Oceanic-oceanic

Slab Pull

• Mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and “pulls” the trailing lithosphere along in a downward force

Sea Floor Spreading/Mid-ocean Ridge

• As the plates move further and further apart, new ocean floor is continuously added

• Where two ocean plates are diverging, molten magma erupts, forming underwater mountains under the ocean

Island Arcs

• A series of volcanic islands formed in an arc-shape when oceanic lithosphere is subducted beneath oceanic lithosphere

• Ring of fire

Subduction Zones

• Oceanic lithosphere subducts underneath the continental/oceanic lithosphere

• Oceanic lithosphere heats up and melts forming magma

• The magma rises forming volcanoes

• The lithosphere subducting is the Benioff zone

Ocean Trenches

• The subducting plate is bent downward to form a very deep depression in the ocean floor

• Mariana

Transform Faults/Boundaries

• Where plates slide past each other

• Earthquakes frequently occur

Volcanic Activity

• Form through subduction of convergent plates and rifting of divergent plates

• Magma in the mantle’s cells slowly rise into the chamber releasing plumes that breach the surface

• Creates more land

• Part of the mid-ocean ridge

Fold Mountains

• Plate tectonics associated with mountain building

• At ocean-continent convergence: The less dense continental plate folds and buckles only on the continental side

• At 2 continental plate convergences: Both buckle and fold with crust thickening on both sides over time

Freeze-thaw Action/Frost Shattering

• Water in joints freezes and expands causing cracks

• Occurs when pressure exceeds rock’s resistance to weathering

• Where: Moisture is plentiful - fluctuating above and below freezing temperatures

• Scree is produced which are smaller, angular fragments of the rock

• Mechanical/physical weathering

Dilatation

• Erosion removes the overlying rocks and the underlying rocks becoming exposed to then expand and fracture

• Where: Very high pressure areas such as confined spaces in the Earth’s interior; removal of weight

• Pseudo-bedding planes: Parallel fractures

• Mechanical/physical weathering

Salt Crystalization

• Caused by decomposition due to salt being left on rock after evaporation

• Sodium expands when left in joints, causing rock to crack

• Where: Hot desert regions with low rainfall and hot temperatures cause salt accumulation as well as polar regions with salt deposition from snowflakes

• Mechanical/physical weathering

Hydration

• Minerals in rock absorb water, expand and change

• Chemical weathering

• Does include some mechanical stress

Hydrolysis

• Rocks react with water and becomes more acidic

• Chemical weathering

• Occurs on rocks with orthoclase feldspar, like granite, and produces clay or salts

Carbonation

• Rainfall combined with dissolved carbon dioxide or organic acid to form a weak carbonic acid

• Chemical weathering

• Occurs on rocks with calcium such as chalk and limestone

Oxidation

• Occurs when iron compounds react with oxygen

• Chemical weathering

• Changes coloration in mineral like rust

Granular Disintegration

• Finer materials being exfoliated gradually

• Certain grains being more prone to expansion and contraction than other - this exerts great pressure on the grains surrounding them and forces them to break off

Block Disintegration

• Successive heating and cooling which causes the expansion and contraction of rocks

Joints

• A brittle-fracture surface in rocks along which little or no displacement has occured

Shear Stress

• Function of gravity pulling the object down

• Increases adds weight to the slope

• Steeper slope = increase in stress

• Bad

Shear Strength

• Resistance of an object to move downhill

• Higher when there is friction or higher cohesiveness (particles being held together)

• Good

Concave Slope

• Slumps happen with this slope

• Declines in steepness with movement downslope

Flow (Mudflow)

• Soil or weaker rocks become saturated with water and flow downhill

• Causes failed landmass/slope to slide, slows down due to firction

• Watery surface, structureless failed landmass with high water content

• Occurs at slow to fast speeds depending on the water content

Fall (Rockfall)

• Rock fragments are detached

• Causes: frost shattering or earthquakes

• steep cliff face is formed

• No/low water content and occurs at high speeds

Soil Creep

• Extremely slow

• Downward progression of rock and soil down a low-grade slope

• Occurs during alternate heating and cooling or wetting and drying

• Low to moderate water

Solifluction

• Frozen slope (occurs during winter) that melts during summer months, causing soil to be saturated with water

• Bottom layer acts as an impermeable layer - a sliding plane

• High water content

• Occurs at slow speeds

Landslide

• Coherent materials (debris/large rocks) moving across a clearly defined sliding plane

• Common along slopes made of rock which allows for more infiltration to occur due to the permeable surface

• High water content

• Occurs at high speeds