Overview of the main topics you will encounter in Module 8
Just for fun!
Traditional sea shanties are work songs that were used by sailors to help them coordinate their physical labor while making the work more enjoyable. This one was used by sailors from Cape Cod…
Cape Cod boys don't have any sleds
Look away, look away,
They slide down dunes on codfish heads
We're bound for Australia.
Cape Cod girls don't have any combs
Look away, look away
They comb their hair with codfish bones
We're bound for Australia.
Cape Cod cats don’t have any tails
Look away, look away
They lost them all in Cape Cod gales
We're bound for Australia.
Getting the Most from the Coast: Cape Cod, Acadia, and Friends
- There are many "types" of coasts (beaches, reefs, mud flats, cliffs, deltas, etc.); here, we’ll especially focus on beaches.
- Waves move LOTS of sand, mostly in, out, in, out…, which sorts by size to give sandy beaches.
- Waves move a little extra sand out during winter storms (breaking waves come in through the air without sand, and go out along the surface with sand).
- And waves move a little extra sand in during summers (a wave surges up the beach a bit faster than the water flows back out, and thus the wave moves a bit more sand in than out).
The Coast Is Friendly—the Ocean Waves
- Waves go slower in shallower water.
- The first part of a wave to approach the coast slows and waits for the rest of the wave to catch up, so the wave "piles up" to break, and turns to come almost straight in.
- But "almost" is not "completely" straight in, and this slight angle drives longshore drift of sand and water along the shore.
- Eventually, some sand is lost to deep water below the reach of waves.
- A beach thus needs sediment supply to balance this loss, or else the beach is eroded.
The Coast Is Friendly—Buoy Meets Gull
- New beach sand is supplied by longshore drift from river-fed deltas, or by erosion of the coast behind the beach.
- Erosion of land behind the beach, and loss of houses, roads, and other things there, is promoted by:
- dams on rivers, which trap sand in reservoirs so the sand cannot reach beaches (for example, the Elwha River dams in Olympic National Park) caused beach loss,
- “dams” along the coast (jetties or groins) that stick out will block longshore drift, trapping sand and letting clean water pass to erode beyond),
- past sea-level rise, which flooded river valleys so river sediment now is trapped where rivers enter bays and does not reach outer beaches (e.g., Chesapeake Bay),
- past deposition by glaciers or other processes that formed coastal land (e.g., Cape Cod) where there are no big rivers to supply sand,
- ongoing sea-level rise or sinking of the land surface along the coast, flooding beaches and washing sand into deeper water.
But Many Coastal Residents are Crabby
- Most U.S. coasts are retreating (about 75%)
- Beaches are retreating because of the processes mentioned in the previous section ("The Coast Is Friendly—Buoy Meets Gull")
- Beaches are especially retreating because humans are raising sea level
- Human-caused global warming is melting glaciers, releasing water that reaches the sea
- And global warming is causing the ocean water to expand
- We also are adding a little more water to the ocean by pumping it out of the ground faster than nature replaces it
- We also contribute to beach retreat by pumping groundwater, oil and gas from beneath beaches, allowing the beach to compact and sink
- Upward or downward motion of the land from natural mountain-building or from ongoing response to the changes in weight from the melting of the ice-age ice sheets is causing beaches to advance or retreat in different areas.