The Lithosphere Flashcards
Describe the timeline of continental drift.
225 mya
- PANGEA, the super continent
180 mya
- LAURASIA (Asia, Europe, Greenland and North America)
- GONDWANALAND (Australia, Antarctica, Africa, India and South America)
Alfred Wagner’s theory of continental drift, 1915
- Convection currents moved the continents
Describe the structure of the earth.
Crust
- Most upper part of lithosphere; the land we know
- Thickness varies: 40km beneath continents, 6km beneath ocean floors
- Difference in rock densities
- Tectonic pates drift with the movement of the athenosphere
Mantle
- High temperatures melt the rock but the pressure hardens the lower part of the mantle
- Lower mantle - 1900km - hard rock
- Upper mantle - 1000km - partially molten rock - athenosphere
- Convection currents mainly occur int he athenosphere
- The boundary between the mantle and lithosphere is called the Mohorovic Dicontinuity “Moho”
Core
- Outer core - 2100km - molten iron and nickel
- Inner core - 2740km diamter - solid material
- Mainly mysterious; thought to be molten rock but high pressures and temperatures render it mainly ambiguous
Explain and give examples for the three different types of plate boundaries.
Diverging
- plates moving apart
- Mid-ocean ridges are formed when two oceanic plates diverge
e. g. the Red Sea
Converging
- Where plates collide together
- Oceanic and Continental
- Subduction zone and trench is created. The more dense oceanic plate slips under the continental plate. A chain eruption of volcanoes can occur along the edge of the continental plate.
e. g. Andes Mountains - Oceanic plates
- The older and therefore more denser plates is subducted under the other, forming a trench. Volcanic mountains and island chains can be formed on the landward side, parallel to the deep sea trench.
e. g. Philippines, Aleutcians and Japan - Continental plates
- Both are of equal density. Forms a folding mountain the continues to build
e. g. Himalayan Mountains
Horizontal Movement
- Where plates slide horizontally pass each other on a fault line. Creates earthquakes.
e. g. San Andreas Fault in California - Pacific and North American plates
Define the different physical weathering processes.
Where rocks of the land surface are broken into smaller pieces but their chemical composition is not interfered with.
Unloading
- When rocks that were once buried deeply underground have the weight of the above pressure removed. This causes the rock to expand and may crack joints parallel to the surface and peel of as sheets
Frost Action
- When water collected in small fissures and cracks freezes and expands by 10%. This forces the rocks to crack. Repeated freezing and thawing widens the cracks.
Organic Action
- Where the germination of seeds and the wedging of roots in rocks exerts pressure, causing cracks to widen. Burrowing animals allow air to penetrate further and may indirectly accelerate weathering.
Some experts believe temperature change or thermal expansion and contraction of rocks as another weathering process. This is relevant in Australia due to the extreme heat exerted in bush fires.
Biological activity, in relation to physical and chemical weathering processes, may be considered the most significant weathering process.
Define the different chemical weathering processes.
Where rocks are decomposed via exposure to water, oxygen and carbon dioxide.
Oxidation
- Oxides are formed when minerals react with oxygen and, when water is involved, hydroxides are formed. Rocks containing iron appear to be rusting.
Solution
- where weak acids dissolve the minerals within rocks and distributes them in solution. Limestone is susceptible to carbonic acid which is carbon dioxide dissolved in water. Limestone caves and Karst landscapes (shaped by dissolving soluble layers of bedrock, usually carbonate-based rocks such as limestone and dolomite) are formed.
Hydration
- Rocks expand as their minerals chemically combine with water. Clay minerals have an enormous capacity for this process. Physio-chemical weathering is the result of this process.
Organic acids
- Produced when water combines with decaying organic material in humus. The acids weather the rock as they seep through the soil.
Most minerals found in the earth’s crust are changed by chemical weathering into new compounds that are stable in the atmosphere, temperature and air conditions on the earth’s surface.
Describe mass movement.
- Where smaller rock particles move due to gravity
- Sometimes fragments of material move together as a unit
- Alternatively, different layers could move at different rates
- Can be rapid (land slide) or very gradual
- Soil creep: where the movement of soil is so gradual on a slope that objects such as trees, fence posts etc. eventually lean to one side.
- Heavy rainfall may trigger a slump of flow (sudden downslope movement of rock and earth).
Describe erosion and depositation.
The land’s degradation includes the erosion of its surface and the eventual and subsequent transportation and deposition of material.
- Ultimately, all materials end up at the ocean floor
- Water, wind and ice are prominent erosive causes
- Running water (fluvial process) and ocean waves are the most common
Describe the different stages of river/stream land shaping.
Hydraulic action
- the power of flowing water
- transports and excavates, especially during floods
Abrasion
- When rock particles that are carried by the water current strike channel walls
e. g. widening of waterfalls
Corrosion
- Where chemical solutions of materials from rock are exposed to the solvents in the water
Describe different river shapes in different land forms.
Mountain
- narrow and fast
- interlocking spurs, river rapids and waterfalls
- steep gradients
Low hills
- substantial down cutting
- river broadens, still fast
- lateral erosion and valley widening
- flood plains and meanders begin to develop
Further on
- river velocity slows
- meandering river, extensive lowland or coastal flood plains
- deltas are formed at river mouth due to deposited sediments; deltas are very unstable landforms due to their easily changeable nature
Bird’s foot delta
- Rapid water mets calm water
- Sediment are dumped as numerous fingers of sand
Cuspate delta
- A river meets strong ocean tides and currents
- Sediments are spread out over a broad front
Arcuate delta
- A single river flows
- supply of sediment is significantly greater than that being taken away
Describe the different processes where wind changes land forms.
Abrasion/ “Sand blasting”
- Most effective where there is little or no vegetation
- Small bouncing trajectories can be carried as high as 1m above ground
- Smaller particles wear away larger rocks
e. g. pedestal rocks
Deflation
- Where fine material is removed by the wind
Reshaping of sand dunes
Describe some different processes where land forms are shaped by ice.
Abrasion
- Glaciers can accumulate, drag, erode and scratch rocks
U-shaped valleys
- where glaciers deepen and widen valleys
Cirques
- Depressions gouged out by glaciers. These are created by repeated thawing and freezing. They hold water, for a time, until a portion of the wall crumbles.
Describe and list the different characteristics of soil.
Texture
- refers to the size of soil particles
Structure
- refers to how the particles clump together in small masses called agregates or peds. Sand doesn’t have any structure. Soil particles with high clay content keep together better. This significantly defines plant growth
Colour
- reflects the presence of identifiable substances
- dark colours - humus content is high
- light colours - less humus content
- red and yellow - oxidation of iron
Acidity and alkalinity
- important characteristic which affects plant growth
Describe soil formation in relation to parent material.
Siliceous parent materials e.g. granite and sandstone, are generally abundant in silica and quartz but low in clay-forming minerals. Thus, low fertility.
Non-acidic parent materials e.g. basalt, are high in ferromagnesium materials (rich in iron and magnesium). Very clayey and fertile soil.
Soil can also be greatly affected by other elements around it e.g. alluvial soil and soils developing in alpine areas with plants like sphagnum moss.
PARENT ROCK - through weathering:
Weathered materials - In situ
- common on hill crests and upper slope
Gravity - Colluvial materials
- common on foot slopes and drainage depressions, mass movement and soil creep
Water - Alluvial materials
- common on alluvial plains, which may be narrow (slopes, tablelands) or broad (plains)
Wind - Aeolin materials
- e.g. sand, loess (silt), parna (clay)
- common in arid environments and in sand dunes in littoral environments
Ice - Glacial materials
- e.g. till, glacial drift, moraine
Describe soil formation in relation to climate.
The ratio of precipitation and evaporation affect how much water is available for weathering, new mineral formation and the translocation of materials.
Where rainfall and abundant, leaching and eluviation can occur. Low temperatures can also reduce weathering rates and increase organic accumulation. Water availability can likewise affect this and the activity of soil organisms.
Describe the role of topography in relation of soil formation.
- Affects how much water is available for weathering, new mineral formation, leaching, translocation of colloids and the downward movement of clay particles.
- Well drained soils occur upslope; water transports materials and accumulates these on lower slopes and depressions.
