Bedforms and storms Flashcards
How do cusps form?
They form as a result of an interaction between fluid motion and sediment transport.
Initial bump in beach face
Swash slows at high tide-> deposition (horn)
Accelerates at low tide (bay)
What are patches?
Sharply defined regions (sand, gravel) that can happen at large scales (kms).
Granular sorting that is self organised and a function of bed roughness
How does granular sorting in patches occur?
Rough bed = turbulence
Sand can’t settle but pebbles can
Pebbles will tend to find other pebbles (arrest each others motion).
On smooth bed, pebbles roll away (but sand able to stay)
Why is there large grain sizes at the top of patches?
Velocity asymmetry
Easier for wave to move up beach then drag away.
Make steeper slopes
How do cyclones form?
Cyclones begin as a collection of thunderstorms
A parcel of warm, moist air is lifted and rises if warmer than surroundings
Pressure drops -> cooling -> condensation
Energy release with condensation = warming tendency
Cools less fast than it would otherwise -> facilitates a rise
The moister the air, the more it can rise.
Sucks in more air from below (positive feedback)
How do tropical storms form?
Late summer (building heat)
Initially a collection of thunderstorms near equatorial ocean
Collective draw of air toward the storms creates a surface low pressure bulb
Starts to draw in more air (regionally) -> More updraft = more suction
Why do cyclones spin?
Coriolis effect and angular momentum
Always spin in the same direction because of the earth’s rotation
Atmospheric pressure gradients (air masses moving from H to L) in the Northern Hemisphere always deflected to the right.
The Coriolis effect appears in the N hemisphere as a reflection to the right
What are cusps?
Crescent-shaped indentations that form on beaches of mixed sand and shingle.
They are formed where there is a junction between sand and shingle.
Once the curving shape is created, swash is concentrated in the small bay that forms in the centre of the cusp.
This creates a stronger backwash that removes material down the beach.
What is imbrication?
Where the current flips pebbles so they’re facing the same direction.
Versions of cyclones e.g hurricanes are based on…
Wind speeds
What is angular momentum?
A conserved quantity (the total angular momentum of a system remains constant unless acted on by an external torque)
Several basic conditions are necessary for hurricane formation:
Warm (27 degree) oceans
60m deep
A location between 5 degrees north and south of the equator. (Without this the coriolis force is not sufficient to create the spinning motion characteristics of hurricanes.)
60% humidity
