Lecture focuses on shallow-water area
Coastal margins- shallow areas are affected by winds and tidal currents
- Typically covered by sand and mud.
- If there is little terrigenous (land-derived) sediment input- carbonates may form.
- Continental shelf slopes off into the abyss
Landscapes are highly variable, depending upon:
- stability of coastal region (uplifting, subsiding, stable)
- Nature of rocks or sediments at the shoreline
- Long-term changes in sea level
- Wave energy
- Tidal energy
Long time scales- Ice ages can shape the coastline e.g. isostatic subsidence and rebound. - Scotland = rebounding + South England is subsiding. T affects relative sea level.
Waves and Tides in Shallow waters
Waves- energy is controlled by wind velocity+ duration and the fetch (distance wave can propogate)
e.g. Over the N. Atlantic blowing west to east- long fetch for waves to build
wind pushes water up and along, gravity is pulling water down- maximum wave height to be recorded- 34m in the pacific by a US Navy tanker.
enormous waves may be responsible for the loss of ships that just go missing- rogue waves- frak event
Waves have wave lengths- L (distance between two crests) and wave height- H (crest to trough). The particle motion is in a circle. Down through the wave, these rotations get smaller as the wave's influence dwindles. Wave period-(T) how long for 2 crests to pass a point.
Wave base= L/2. Water depth=D
Shallow water waves will influence the sea bed D<L/2 Deep water waves have no influence on the sea bottom D>L/2
When deep water waves become shallow water waves- water slows down on contact with the sea bed- friction- and wave builds. - Heightened and sharpened crests. Length decreases.
In the surf zone- gravty acts on wave crests- water topples over
When various wave frequencies coalesce and disperse- swells can build into waves with…