1. Coasts

2. Coasts Coastal areas join land and sea
Coasts are temporary junctions (of land and sea) that are subject to rearrangement by waves, tides, sea level, biological processes and tectonic activity
50% of the world’s population lives on the coast
The term ‘coast’ includes the shore (where ocean and water meet) as well as marshes, dunes, and cliffs inland of the beach

3. You are going to coast through this chapter
Remember coastal margins?
These were the submerged portions of continental crust
Coastal regions are constantly subject to change, most dramatically by tides and erosion (short-term effects) and rising or lowering sea level (long-term effect)
The coast is an active and dynamic place

4. Sea level 18,000 years ago during last ice age

5. Year 2100: Projected (extreme) sea level rise of 200ft

6. Changes in sea level: eustatic
Several factors can influence global, or eustatic sea level variations
Sea level is lower during periods of glaciation (more water held up in ice) and higher during warm periods (when glaciers are smaller)
High rates of seafloor spreading produce larger rises, decreasing the volume of the ocean basin compared to slower rates of spreading
Thermal expansion: water occupies a greater volume when warmed

7. Changes in sea level: local
Other factors can influence regional or local sea level changes
Isostasy; continental plates weighed down by ice or sediment sink deeper into the aesthenosphere, raising local sea level!
Wind, currents, storm surges, El Niño/La Niña can force more (or less) water on the shore

8. Isostasy and Local sea level change
Ice
Continental crust
LITHOSPHERE
Oceanic crust
AESTHENOSPHERE

9. Isostasy and Local sea level change
Ice
Continental crust
LITHOSPHERE
Oceanic crust
AESTHENOSPHERE

10. Local sea level change
The flooding Mississippi River delta is one example of subsidence or land sinking, caused by an accumulation of several hundred feet of sediments forcing the lithosphere to sink deeper into the asthenosphere
The continent of Antarctica is another example; massive ice sheets weigh down the continent raising local sea levels

11. Erosion
The immense power of the waves abrades the coasts and can cause erosion, the removal of coastal material
When erosive forces dominate over depositional forces, erosion occurs
Most rapid on high energy beaches; areas frequently battered by large waves (ex. Maine, southern tip of South America and Africa)
When deposition meets or exceeds erosion, the coast is stable or growing, respectively
Low energy beaches (ex. NJ to Florida)

12. Erosion
Erosion tends to produce a smooth coastline (imagine what erosion does to sea cliffs over time)
The sediment eroded away from the coast eventually collects as beaches and may actually protect the shore from the incoming energy (and erosive power) of the waves

13. Let’s go to the beach…
A beach is a zone of loose particles that covers part of a shore (dunes, vegetation and/or sea cliffs are technically not part of the beach)
Beaches result when waves (or rivers) transport sediment – usually sand – to the shore
Beaches are constantly changing – what you see during our field trip to Smith Point is different from what your children will see (or what your parents have seen)

14. What Smith Point used to look like
Courtesy of Prof. Pamela Lynch

15. What Smith Point used to look like
Courtesy of Prof. Pamela Lynch

16. It’s a shore thing
The material that makes up a beach can range from boulders, cobbles, pebbles and gravel to very fine silt
The black beaches of Hawai’i are made of lava!
Some beaches consist of shells or coral fragments

17. Parrotfish Poop = Paradise
Parrotfish feed on coral engulfing the animal and its CaCO3 skeleton; they ingest the polyp and excrete the CaCO3, which ends up on local beaches as soft, fine sand between your toes!

18. Beaches have distinct profiles
In general, the flatter the beach, the finer the material from which its made
Water from waves washing onto the beach carries particles onshore (“swash”); water returning to the ocean (“backwash”) carries material back to sea
The amount of particles transported by the swash and backwash are not always equal, resulting in sloped beaches

19. Beaches have distinct profiles
The berm is an accumulation of sediment that runs parallel to shore, and marks the normal limit of sand deposition by wave action
The peaked top of the highest berm is called the berm crest, and is usually the highest point on the beach; it corresponds to the shoreward limit of wave action during the most recent high tides

20. Is Oceanography fun? Shore!

21. Is Oceanography fun? Shore!
The steepness of beaches changes with storms and the seasons
Summer and calm periods build up beaches
Winter and storms erode and flatten beaches
WHY???

22. Light versus heavy wave activity
During light wave activity, much of the swash soaks into the beach, and so backwash is reduced
Results in a net movement of sand up the beach
During heavy wave activity, the beach is saturated with water from previous waves, so very little swash soaks into the beach; more particles are moved offshore by backwash
Results in a net movement of sand away from the beach

23. Summer versus winter beaches
Light and heavy wave activity alternates with the seasons
Light wave activity dominates during summer, and so a wide, sandy berm develops
Heavy wave activity dominates during winter, and transports sediment/particles offshore
A wide berm developed over many months during summer can be destroyed in hours by high-energy winter storm waves

24. Wide, prominent berm

25. No (or reduced) berm
Sand deposited offshore

26. Longshore currents
Longshore currents transport sand along the coastline
Recall that most wind waves approach the shore at an angle, and then refract to break nearly parallel to the shore
With each breaking wave, swash moves onto the beach at a slight angle, then gravity pulls the backwash straight down (no angle); this zig-zag movement of water along a shore is called a longshore current

27. c c

29. Break the grip of the rip
Rip currents is a dangerously strong current of water flowing offshore with speeds averaging 1-8 feet per second!
Water streams along the shore until it finds an exit back to sea, usually a narrow trench between sandbars

30. To escape a rip current, it is extremely important to swim parallel to shore as you cannot outswim the rip tide current and you will eventually exhaust yourself (and drown) in the process. The rip current is found only along a narrow portion of shoreline
Topography and surging seas determine whether a rip tide will occur; can be visualized by rough, brown water offshore

31. Longshore currents
Longshore currents transport sediments away from the beach and towards regions ‘downwind’
Jetties, groins, and breakwaters serve to intercept, or stop the transport of sediment away from beaches
Longshore current

34. Barrier Islands
Depositional coasts (coasts where depositional forces dominate over erosive) may develop narrow, exposed sand bars that run parallel to, but are separated from, land; known as barrier islands
Fire Island, NY; Atlantic City, NJ; Ocean City, MD; and Miami Beach, FL are barrier islands!

35. Barrier Islands
Barrier islands protect the coast behind them, but are very unstable themselves

37. Net transport of sediment is from east to west
What about Long Island?
Net transport of sediment is from east to west

38. A state park your great-grandparents never had…
Since the Fire Island lighthouse was constructed 100 years ago, nearly 5 miles of barrier island have been added to the west forming what is now Robert Moses State Park!

39. Hurricane Paths on Long Island

40. The importance of dunes
Dune plants prevent erosion by trapping sediments in their roots
Removal (or destruction) of beach vegetation, and the hardening of shorelines (bulkheads) increases erosion
Plant rhizomes can extend feet from the plant!
Courtesy of Prof. Pamela Lynch

41. And don’t forget about overpopulation!