Wrap Up

Review of the main topics and ideas you encountered in Unit 8.

Getting the Most from the Coast: Cape Cod, Acadia, and Friends

• There are many coast “types” (beach, reef, mud flat, cliff, delta, etc.; we’ll especially focus on beaches).
• Waves move LOTS of sand, mostly in, out, in, out…, which sorts by size to create sandy beaches.
• Waves move a little extra sand out during winter storms (breaking waves come in through air without sand, go out along surface with sand).
• Move a little extra in summers (surge up the beach a bit faster, moves a bit more than return flow).

The Coast Is Friendly--the Ocean Waves

• Waves go slower in shallower water;
• First part of the wave slows as it nears coast and waits for rest of wave to catch up, so piles up to break, and turns to come almost straight in;
• But still has a slight angle, driving longshore drift of sand and water;
• Eventually, some sand is lost to deep water below the reach of waves;
• Beach needs sediment supply to balance this loss.

The Coast Is Friendly--Buoy Meets Gull

• New beach sand by longshore drift from river-fed deltas;
• Or by erosion of coast behind beach;
• Lose longshore drift from river-fed deltas by
  • dams on rivers (Elwha dams in Olympic caused beach loss);
  • “dams” along the coast (jetties or groins that stick out, block drift to trap sand, let clean water pass to erode beyond);
  • past sea-level rise, flooded river valleys so sediment fills bays and doesn’t reach outer beaches (e.g., Chesapeake);
  • past deposition (especially by glaciers) forming coastal land (e.g., Cape Cod) without big rivers to supply sand.

But many coastal residents are crabby

• Most U.S. coasts retreating (about 75%);
  • from past sea-level rise and glaciation, dams and coastal modifications (see the previous point, "The Coast Is Friendly--Buoy Meets Gull");
  • from sea-level rise now (from warming expanding water and melting ice, plus groundwater mining, with worries about the future of huge ice sheets);
  • from pumping of groundwater, oil and gas allowing compaction and sinking;
• Regions pushed down by ice-age ice may be rising; those bulged up before ice-age ice sink faster; mountain-building also matters.