Week 13 Flashcards
Earthquakes
The vibration of Earth produced by the rapid release of energy along faults in Earth’s crust.
Energy released as vibrations (seismic waves) radiates in all directions from its source, the focus.
Epicentre
The point on Earth’s surface directly above the focus is the
Storage of Energy in Faults
Rocks on either side of a fault or planar feature deform under tectonic forces, bending and storing elastic energy, creating strain.
Release of Energy in Earthquakes
When friction along a fault is overcome, slippage occurs at the focus. The deformed rock “springs back” to its original shape, releasing energy as vibrations (earthquakes) through elastic rebound.
Types of Seismic Waves: Body Waves
Body waves travel through Earth’s interior
Primary (P) Waves
Push-pull (compress and expand) motion, changing the volume of the intervening material.
Secondary (S) Waves
Shake motion at right angles to their direction of travel. Take longer to travel than P waves
Sequence of body waves
P waves arrive first, then S waves, then L waves
Rayleigh (R) Waves
rolling motion
Love (L) Wave
horizontal shearing
How Do We Find the Distance to an Earthquake Epicentre?
A travel-time graph shows the time gap between P and S wave arrivals.
→ The longer the delay between P and S waves, the farther the recording station is from the epicentre.
→ This time difference is used to calculate the distance to the quake.
Locating the Epicentre of an Earthquake
Draw a circle around each seismic station with radius = distance to epicentre
Where all 3 circles intersect = epicentre location
(This method is called triangulation)
Earthquake Belts
~95% of earthquake energy is released along plate boundaries
Caused by plates sliding against each other
Magnitude Scale (Richter)
Based on amplitude of largest seismic wave
Accounts for distance from epicentre
Use amplitude + distance to determine magnitude from a chart
How Tsunamis occur
result from vertical displacement along a fault located on the ocean floor, a large undersea landslide triggered by an earthquake, or other disturbances (e.g. meteorite impact).
Distribution of Volcanoes
Most volcanoes occur along plate boundaries
Hotspot volcanoes form within plates
– Caused by stationary mantle plumes generating magma
Mafic Magmas
- Low viscosity (runny) due to low silica
- Low volatile content
- Erupt gently
- Common at hotspots and divergent boundaries
Intermediate to Felsic Magmas
- High viscosity (stiff & gooey) due to 60–70% silica
- High volatile content
- Erupt explosively
- Common at convergent plate boundaries
Calderas
- Formed when the summit collapses after a massive eruption
- Release of pyroclastic debris & gases through ring fractures
- Among the most devastating volcanic events
Frankenstein & the “Year Without a Summer”
- 1816: Known as “Eighteen Hundred and Froze to Death” in the US
- Caused by global cooling after a major volcanic eruption
- Crop failures, snow in summer, famine
- In Europe, bad weather kept Mary Shelley & others indoors in Switzerland
- Led to the creation of Frankenstein during a ghost story challenge
mimetolith
a natural topographic feature, rock outcrop, rock specimen, mineral specimen, or loose stone with the shape of something else
Concretions
Bodies of cemented sediment. Commonly formed in marine sediment with abundant organic matter. In the process of eating the organic matter (containing carbon), certain bacteria release bicarbonate into the pores of the sediment.
Nucleation of Concretions
Combines with dissolved calcium in the porewater to form crystals of calcite (calcium carbonate), which cement the sediment grains together. This cementation is often localized around a nucleus, such as a fossil, forming discrete bodies of cemented sediment
Differential Erosion
More resistant to weathering and erosion than their host sedimentary rocks within which they grew. When the host rock is eroded away, the concretions appear strewn over the eroded surface.
Crossbedding
A sedimentary structure produced by the migration of bedforms (ripples and dunes) under the influence of a water or wind current. Sediment particles transported in a current come to rest on the down current side of the bedforms, forming laminations at a high angle to the main bedding surfaces.
Cave Deposit formation
Over long periods of time, continued dissolution can produce large underground tunnels. Tunnels are drained of water if the water table is lowered- this leaves behind an empty, air-filled space that we call a cave.
Speleothems
Cavern features produced by the minerals precipitated from dripping water
stalactites
Over long periods of time, precipitation of calcite from dripping water produces icicle shaped bodies of travertine
stalagmites
Calcite precipitation from water on the floor of a cave, produces upward-oriented mounds
Soil: The Foundation For Crops
a combination of mineral and organic matter, water, and air. It is the portion of the regolith (rock and mineral fragments produced by weathering) that supports the growth of plants
Typical components in a soil that yields good plant growth
Mineral matter provides the important inorganic nutrients for plant growth. In addition, it also provides a substratum for root growth and gives soil “structure.”
Water’s role with soil
The transport medium for nutrients (and air) to be taken up by plant roots.
Factors that control soil formation
- parent material
- time
- climate
- plants and animals
- slope
Soil Texture
Primarily controlled by the grain size of mineral matter.
Clay-rich soils retain lots of water and tend to contain lots of nutrients
At the opposite extreme, gravel- and sand-rich soils drain very quickly
Loam: A happy medium
For most crops, the most desired type of soils is loam – a mixture of clay, silt and sand
provides adequate water and nutrient retention while allowing sufficient drainage
