Overview
This lecture covers coastal processes and hazards, including wave dynamics, shoreline features, erosion, deposition, and the differences between types of coasts.
Importance of Studying Coastal Processes
- 75% of the U.S. population lives in coastal areas, including Great Lakes coasts.
- Most large U.S. cities are located on or near coasts.
Key Coastal Terms and Zones
- The coast is the zone from water to a major change in landforms.
- The shore extends from high to low water, with the shoreline marking the contact between land and sea.
- The beach is sediment in transit along the shore.
- Longshore currents transport sediment parallel to the coast.
Coastal Processes & Morphology
- Coastal morphology is shaped by storms, wind, waves, tides, sea level changes, and human activities.
- Coastal features include beaches, bluffs, underwater bars, sea cliffs, dunes, and barrier islands.
- Coastal systems are a battle between erosion and deposition.
Wave Dynamics
- Ocean waves are caused by wind's friction on water, with energy—not water—moving forward.
- Wave size depends on wind velocity, duration, and fetch (distance wind blows over water).
- Wave terms: crest (top), trough (bottom), amplitude, wave height, wavelength, period.
- Wave velocity = wavelength / period.
- Wave energy increases by a factor of four when wave height doubles.
- Circular orbital motion of water particles decreases with depth down to the wave base.
Waves Approaching Shore
- As waves enter shallow water, friction slows the base, increasing height and steepness, eventually forming breakers.
- Surf is turbulent water from breaking waves; swash moves water up the beach, backwash returns it to sea.
- Wave refraction bends waves to hit shore nearly parallel, focusing energy on headlands and dispersing it in bays.
Erosion and Deposition Features
- Erosional features: wave-cut cliffs, platforms, marine terraces, sea arches, and sea stacks.
- Depositional features: spits (elongated ridges), baymouth bars (bars sealing off bays), tombolos (sand ridges connecting islands), barrier islands (narrow offshore sand ridges).
Sediment Transport and Currents
- Beach drift and longshore currents move sediment in a zigzag pattern along the shore.
- Rip currents flow seaward through gaps in sandbars; swim parallel to shore to escape them.
Types of Coasts
- Emergent coasts: uplifted land (wave-cut platforms, marine terraces), common on active margins.
- Submergent coasts: land subsidence or rising sea level, creating estuaries (flooded river mouths).
U.S. Coastal Comparisons
- Atlantic & Gulf Coasts: passive margins with barrier islands, absorb storms, no active tectonics.
- Pacific Coast: active margin with tectonic activity, shrinking beaches due to sediment trapping by dams, sporadic erosion.
Key Terms & Definitions
- Coast — area from water to a major landform change.
- Shoreline — line where land and sea meet.
- Longshore Current — current moving parallel to the shore, transporting sediment.
- Wave Refraction — bending of waves as they approach shore.
- Rip Current — narrow, fast current flowing away from shore.
- Spit — elongated sand ridge extending from land into a bay.
- Baymouth Bar — sand bar crossing the mouth of a bay.
- Tombolo — sand ridge connecting an island to the mainland.
- Barrier Island — offshore sand ridge parallel to the coast.
- Emergent Coast — coastline rising relative to sea level.
- Submergent Coast — coastline sinking or sea level rising, forming estuaries.
Action Items / Next Steps
- Review textbook terms: spit, baymouth bar, tombolo, estuary.
- Prepare for next lecture on coastal erosion.