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Place 07 · The Northeast Coast · Chapter 7 of 7
Rock, Sand and Rising Water
Maine’s coast is made of rock that a glacier scraped bare; New Jersey’s is made of sand that will not sit still. Guess which one the rising sea is having an easier time with.
About 15 minutes · 1 video · 1 live sea level map · 2 quick activities
Start here
Two coasts, one ocean
North of Cape Cod the Northeast coast is mostly rock: Maine’s coastline runs about 3,500 miles in and out of drowned glacial valleys, and only about 2% of it is sandy beach. South of Cape Cod it turns to sand: long barrier islands from Long Island to New Jersey and beyond, separated from the mainland by bays and marshes. Rock mostly stays put; sand gets carried away and, if it is lucky, brought back.
Watch this
See it move
Explore Nature — Outside Science (inside parks): Tidepools in Acadia National Park. Two minutes poking around the tide pools of Maine’s only national park, with audio description included. The periwinkles did not consent to being filmed.
While you watch, look for
- Which animals and seaweeds live in Acadia’s tide pools
- What makes life between the tides so hard
- Something you did not expect. Hold onto it.
The short version
Three things going on here
The rock
Life in stripes
On Maine’s rocky shore, life sorts itself into bands called zonation, just like the tide pools of Place 02. High up, barnacles and periwinkles survive hours out of water; in the middle, rockweed drapes over the rocks; low down, Irish moss and mussel beds appear only at the lowest tides; and below them grows kelp. Maine’s tides make the stripes wide: the tidal range runs from about 8.7 feet at Kittery to 18.4 feet at Eastport.
The sand
Islands that walk
Waves that hit a beach at an angle push sand along the shore in longshore drift, the same river of sand from Place 02. Cape Cod itself was dumped by a melting ice sheet, and since then waves have eaten its glacial cliffs while longshore currents carry the sand off to build spits and hooks. A barrier island goes further: storm waves wash sand over the dunes to its back side, and the whole island rolls slowly toward the mainland.
The water
The sea rises, the land sinks
NOAA’s tide gauge at Atlantic City shows sea level rising about 4.25 mm a year since 1911, about three times the global average for the 20th century; at Portland, Maine, it is about 1.97 mm a year. Part of the difference is the land: as the old ice sheet’s weight came off, the land it covered rose and the Mid-Atlantic, like the other end of a seesaw, sank; compacting sediment and groundwater pumping add to the sinking along the Jersey shore. In October 2012, Hurricane Sandy’s storm tide at the tip of Manhattan reached a record 14 feet above the average lowest tide.
Photos: Howard Herdi, Pok Rie, Ray Bilcliff / Pexels
Play with it
Raise the sea yourself
NOAA’s Sea Level Rise Viewer shows which parts of the coast would flood if the sea rose by different amounts. Search for Atlantic City, New Jersey, drag the sea level slider up one foot at a time, and watch the barrier island and the marshes behind it; then search for Portland, Maine, and compare.
Interactive map: NOAA Office for Coastal Management, Sea Level Rise Viewer (coast.noaa.gov/slr).
Two questions to answer while you are in there
- At Atlantic City, how many feet of sea-level rise does it take before the back of the barrier island and the marshes start to flood? What goes first: the ocean side or the bay side?
- Compare Atlantic City with Portland, Maine, at the same amount of rise. Which coast loses more land, and how does rock versus sand explain it?
Try it yourself
Check yourself
Try it
Rock, Sand or Rising Water?
Eight quick calls about zones, sand and sea level.
Try it · interactive
Tide Zones
Raise and lower the tide on a Maine rocky shore and find who lives in each zone, from barnacles and periwinkles to rockweed, mussels, Irish moss and kelp; then switch to a sandy barrier beach, push sea level up, and watch the island roll toward the mainland.
Open Tide Zones in its own window (opens in a new tab).
Words you will hear
Four terms, that is all
Intertidal zone
Shore between the highest and lowest tides
Zonation
Life arranged in bands by height on shore
Barrier island
Long sandy island parallel to the mainland coast
Longshore drift
Sand carried along the beach by angled waves
Check your understanding
Practice the whole chapter
Everything in this chapter, in eight quick questions. Retry as often as you like. Read the feedback on every answer, right or wrong, because that is where the learning is.
Practice
Practice: Rock, Sand and Rising Water
Eight questions covering the video, the three cards, the four terms and the interactive above.
If you want more
Go deeper
- Oceanography 101 (MiraCosta) 15.11 — Rocky Intertidal Zonation — LibreTexts · 5 minutes
- Webb 13.2 — Longshore Transport — LibreTexts · 5 minutes
- NOAA Tides & Currents — Sea Level Trends — NOAA · explore the map
Photo credits (Pexels): Leah Newhouse, Frank Rietsch, Howard Herdi, Pok Rie, Ray Bilcliff.