Rocks CIE Geography

lithosphere

lithosphere

tectonic plates are part of the lithosphere, which is the rigid outermost layer. combines the crust and upper mantle

oceanic crust

mainly composed of basalt, volcanic rock, and if generally 5-10km thick

continental crust

primarily made of granite, which are lighter and less dense, and generally 30-70km thick

size of tectonic plates

there is large diversity in size and thickness of the plates

movement of tectonic plates

the plates are in constant motion, at a rate of a few centimeters per year and it is not unidirectional

major plates

the pacific, north american, eurasian, african, indo-australian, antarctic and south american paltes

minor plates

many minor plates sich as nazca near south america and cocos in the pacific ocean

divergent boundaries

plates move away from each other, this movement typically occurs in oceanic crust, resulting in formation of mid-ocean ridges eg mid atlantic ridge

convergent boundaries

one plate subducts beneath the other, leading to features like mountain ranges, volcanic activity and the formation of deep ocean trenches

conservative boundaries

the plates slide past each other horizontally such as the san andreas fault in california

convection currents

primary mechanism for plate movement. Heat from the earth’s core creates convection currents in the semi-fluid asthenosphere beneath the lithosphere, causing the plates above to move

slab pull

occurs at the denser edge of one plate subducts beneath another, pulling the rest of the plate with it

ridge push

the creation of new material at mid-ocean ridges causes older material to be pushed away from the ridge, driving plate movement

divergent landforms

• mid ocean ridges

• rift valleys

convergent landforms

• orogenesis

• island arc/volcanos

  • ocean trenches

sea floor spreading

the process at divergent plate boundaries where as the plates separate, magma from the mantle swells up, cools and solidifies, forming new oceanic crust. causes gradual expansion of the ocean floor.

benioff zones

area of significant seismic activity associated with subducting plates.

orogenesis

when two continental plates collide, the compression forces the crust to buckle and fold, forming mountain ranges

volcanic island arc

chains of islands formed along convergent tectonic boundaries as volcanoes formed grow above sea level.

freeze-thaw weathering

a cyclic process that occurs in climates with temperatures that fluctuate around 0°C. The water seeps into cracks/pores in the rock when it is warm. When the temps drop below 0°C, the water turns to ice in the rock and expands, exerting huge pressure, enough to fracture rock through repeated cycles.

Heating/Cooling

the expansion and contraction of rocks due to temperature change. in the day, the rock heats up and expands before cooling and contracting at night. different rocks expand at different rates, causing cracks to form

salt crystal growth

when salt water enters cracks in rocks and once the water evaporates, salt crystals are formed and grow, which causes cracks to be enlarged.

pressure release

when rocks formed under great pressure are eroded. this causes them to be exposed ans the pressure to reduce. this allows the rocks to expand and forms cracks parallel to the surface.

exfoliation

where the outer layers of rock peel away

hydrolysis

where minerals react with water, resulting in the formation of new minerals, often clays and the release of soluble ions. occurs in moist and acidic areas

hydration

the absorption of water into the crystal structure of minerals, which leads to changes in the physical properties, which weakens the rock.

carbonation

CO2 from the atmosphere or soil mixes with water to form weak carbonic acid which reacts with calcium carbonate in rocks like limestone to erode them

joints and bedding planes

natural fractures which allow deeper penetration of weathering agents`

peltier diagram

a graphical tool that shows the interplay between temperature and rainfall in affecting weathering types and rates

slope angle

slope processes lead to the increase or decrease in the gradient of the slope.

heaves

from the expansion and contraction of soil, due to moisture and temperature fluctuation

flows

the downward movement of saturated soils and debrise

earthflows

a gradual downslope movement of saturates soil and weak rock. can be rapid too after a prolonged rainfall or snowmelt

mudflows

rapid and fluid movements of a mixture of water, soil and rock debris

slides

when regolith or a rock moves as a coherent block along a clearly defined slip plane

translational slidews

when material moves down a slope down a relatively flat planes, often following bedding planes, joints or faults in the rock.

rotational slides

concave sliding plane, leading to rotation of the sliding material, often occurs in soft materials eg clay

rockfalls

the rapid movement of falling rocks down a steep slope or cliff

rainsplash erosion

when raindrops hit the soil surface, leading to detachment and displacement of soil particles

sheetwash erosion

a form of surface runoff characterised by a thin layer of water over the ground surface, critical in the transportation of soil sediments

rill erosion

small channels develop due to surface irregularities, leading water to concentrate in certain paths.

gullies

with time and continued water flow, rills can become large and more permanent erosional features

retaining walls

walls that support soil laterally, and are used in urban areas to prevent landslides

terracing

where steps are cut into the soil side to reduce runoff and erosion

pinning

steel rods or bolts are drilled deep into the slope’s material, which act as anchors to hold the slope material together.

netting

draping wire nets over the face of slopes, to catch and holod falling rocks and debris

afforestation

planting trees and vegetation to increase the mechanical strength of the slope through root systems, binding the particles together