Flashcards in Depositional landforms Deck (25):
How are beaches formed?
Accumulation of material from cliff erosion 5%, offshore sea bed 5%, rivers 90% (suspended/bed load from river mouths).
Characteristics of a sand beach (with ridges/runnels)
Small particles are compact so little percolation during backwash, little energy is lost to friction so material is carried back down beach, forming a gentle gradient.
Characteristics of a shingle beach (pebbles/cobbles)
Swash is stronger than backwash (rapid percolation in large airspaces), creates steep beaches as there's a net movement of shingle onshore that stays at the top.
How is a ridge/storm beach formed?
Storm waves hurl pebbles/cobbles to back of beach.
What is a berm and how is it formed?
A smaller ridge, develop at mean HTM because of deposition at top of swash.
What is a cusp and how is it formed?
Regular arc pattern of sed, semi-circular depressions. Formed by lots of waves reaching same point and when swash/backwash have similar strengths.
Why are ripples formed?
In sand due to orbital movement of water in waves
What do beach profiles do?
Respond to changes in wind strength/wave energy, with an equilibrium profile (balance between erosion/depo).
What do high energy waves do?
Destructive, move sed offshore, create flatter profiles resulting in shallower water, more friction, less energy.
What do low energy waves do?
Constructive, sed moved onshore forming steeper profiles with deeper water, less friction, more energy.
What are spits and how are they formed?
Narrow beaches attached to land at one end and extend over an indentation in the coastline (cove/bay/
estuary). Formed by LSD in one dominant direction. Sheltered area behind has less wave energy, so more deposition (salt tolerant veg may colonise, a salt marsh).
Facts about Orford Ness, East Anglia (Spit):
NE dominant wind/waves, so LSD from N to S. Formed across estuary of River Ore, grows parallel to the coast.
What are onshore bars?
Spit that grows all the way across an indentation so it joins the land on the other side. Lagoon of water formed on landward side.
Facts about Slapton Sands, Devon (Onshore bar):
100m wide, mostly shingle but no obvious pattern of sed sizes and little LSD on E. Partly formed by onshore movement of sed in the post-glacial sea level rise.
What are tombolos?
Beaches connecting mainland to offshore island, often elongated spits.
Facts about Chesil, Dorset (Tombolo):
30km shingle, was either a spit or formed by onshore movement of sed. Not formed by LSD because sed in East would be smallest (E at Portland ridge is 13m, W at Burston Bradstock its 7m). Originally uniform distribution of sed sizes, but SW LSD currents have only been able to transport smaller sed particles to the West.
What are salt marshes?
Low-energy environments of vegetated areas on deposited silts/clays. Twice daily the area is inundated then exposed. Plants (eelgrass) trap sed and increase marsh height and roots stabilise the sediment.
The differences between a high and a low marsh?
High marsh has a shorter daily submergence and therefore less saline conditions than the low marsh (on the seaward side). High parts also have lots of deposition due to high WM and low energy water.
What are saltpans?
Shallow depressions between creeks that trap water as the tide falls, often devoid of vegetation.
What does Salt marsh development depend on?
Rate of sediment accumulation (about 10cm/yr), deposition from slowing rivers and flocculation.
What are deltas?
When lots of sediment deposited by rivers/tidal currents accumulates at the mouth of rivers, when deposition rate exceeds removal by waves and tides (low energy).
Where do deltas form?
Where rivers with large loads enter the sea and the continental shelf margin is a platform for accumulation.
What is the structure of a delta?
Upper delta plain (inland) has only river deposits, lower is in the inter-tidal zone (often submerged) has river/marine deposits and submerged (below LWM) has marine sed and is the seaward growth.
What are the 3 types of delta?
Cuspate (pointed coastline extension, shaped like a V by regular currents from opposite directions). Arcuate (lots of sed so grows seawards, wave action smooth's the leading edge). Birds foot (distributaries in branching pattern, river sed supply exceeds removal by waves).