Marine and Coastal Processes

MOHAMED ERSHAD NP

Reg No: 2015255014

Coastal processes occur where waves break on a shore, not only on ocean/sea coasts but also on lakes/ponds

WavesCurrents Still-water depositionBiological activityTides Sea level rises

Waves are usually caused by wind and controlled by wind speed.

Waves are oscillations: a water particle moves in an elliptical orbit as a wave passes and returns to its original position.

Main characteristics: height (amplitude), wavelength, wave period (or frequency).

Wave motion dies out with depth.

Surface water has more velocity than that of bottomWaves usually approach a shore obliquely

swash comes onto a beach obliquely and backwash leaves downslope (perpendicular to the beach), resulting in a small net translation of water and sediment in the direction of the original waves. The water is not flowing parallel to shore, but that’s the net effect of two processes.

Longshore drift causes a continual re-working of sediment on a beach and translation parallel to the shore.

Longshore Drift

Rip currents, also known as riptides or undertows, result when water piles up on a beach. This is unstable, and the water will make it out to sea somehow.

A rip current is a fast-moving current that carries water away from shore in a concentrated stream. It does not pull you under, but does carry you out to sea.

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The moon does not simply orbit the earth. The earth also orbits the moon, but in a very small orbit.

Due to the combination of gravitational and centrifugal forces ,results in a twice daily rise and fall of sea-level.

The earth-sun system also produces this effect, and the two are super-imposed, resulting in a twice-daily rise and fall , with variations throughout the course of the moon’s orbit (monthly).

•Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides.•Storm tide defined as the water level rise due to the combination of storm surge and astronomical tide

Storm surge

It is a series of waves generated by the sudden displacement of the sea-bottom due to an earthquake, a submarine landslide, an asteroid impact, or a volcanic explosion.

Tsunami are very long & lengthy waves, so they move fast. In deep water, most tsunamis have fairly small amplitude (like a half-meter or meter). When they feel bottom and start to crest, a huge amount of water stacks up and can result in devastating coastal flooding.

Sometimes, a tsunami falls then rises, sometimes it rises then falls, depending on how the fault moved and where the site is relative to the fault.

It’s very hard to measure sea level in absolute terms, so we really talk about relative rises and falls of sea level.

Sea level changes can be due to

subsidence as underlying sediments compact (porosity decreases),

cooling-driven subsidence (or heating-driven uplift)influx of ice from melting glaciers expansion or contraction of mid-ocean ridges, filling in of oceans with sedimentsmovement of fault

•When sea levels rises, areas that were underwater get deeper (finer sediments get deposited) and areas that were sub aerial before might now be subjected to marine erosion. We can often see erosional features.

•When sea level falls, it exposes submarine areas.

• As well as exposing previously-submerged areas to streams, wave erosion might start on the new coast

There are three types of coastal landforms:

Erosional coast Transportational coastDepositional coast

“Depositional” coasts are dominated by deposition of sediments and re-working by long shore drift.

•Spits•Barrier Island•Deltas

It is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end

Long thin sandy stretch of land, parallel to mainland coast that protects the coast from the full force of powerful storm waves

Deltas are wetlands that form as rivers empty their water and sediment into another body of water, such as an ocean, lake or another river

If sediments are not reworked at all, you get a river-dominated delta like the Mississippi.

If the sediments are re-worked by long shore drift, you get a wave-dominated delta like the Nile’s.

If the sediments are re-worked by the on-shore/off-shore currents of the tides, you get a tide-dominated delta like the Brahmaputra’s

•The waves attack the base of the cliff through the processes of abrasion, corrosion, hydraulic action and attrition.•Over time the cliff will be undercut and a wave-cut notch is formed.•Eventually the cliff becomes unstable and collapses. Further cliff retreat will form a wave-cut platform.

Sea caves result where an easily eroded piece of rock is removed.

Sea caves

A sea arch happens when a sea cave or two goes all the way through.

sea arch

If the arch collapses, the seaward part is still there and is a stack

(Sea stacks are erosional remnants; with a cave cutting through, it's a sea arch.)

Sea stacks