Shorelines and Shoreline Processes

Wave Dynamics: need to be familiar with:

• crest, trough, wave length, wave height, period, wave base

Wave Generation

• wind, earthquakes, falling earth, volcanic explosions
• of these wind and the distance over which it blows - the fetch - is most important

Shallow-Water Waves and Breakers

• When a wave gets into water of depth less than half its wavelength, it begins to feel the bottom, causing it to pile up, and break.

Nearshore Currents

• breaker zone, surf zone
• Wave Refraction caused by feeling the bottom and slowing.
• Longshore Currents caused by waves not approaching the shore exactly straight on.
• Rip Currents caused by rapid return flow from breaking waves - caused by specific bottom topography.

Shoreline Deposition

• beaches, spits, baymouth bars, barrier islands

Beaches: a deposit of unconsolidated sediment extending landward from low tide to a change in topography such as dunes, a cliff or permanent vegetation

• Terms such as: backshore, berms, face, foreshore
• Sculpted predominantly by: longshore drift
• Manmade attempts to manage the sand budget on an active beach: groins
• Commonly made of quartz sand, but beautiful examples of shell beaches, and black beaches composed of ground basalt.

Seasonal Changes

• "summer" vs "winter" beaches: terms relating to sandy beaches in the relative calm of summer which are converted to rocky beaches in the winter when the larger storms move much of the sand offshore.

Spits, Baymouth Bars, Tombolos: various accumulations of sand marking local low energy environments.

Barrier Islands

• Two possible origins: submerged beach ridge (changed sea level) vs detached spit?

Nearshore Sediment Budget

• Relative balance of additional sediment vs removal
• Submarine canyons can provide major conduits out of the beach system for erodable sediment.
• Dams remove sediment when they provide local base-levels - this means the sediment supply to the delta/ocean is perturbed - may lead to erosion of delta (Louisiana) or down-current beaches.

Shoreline Erosion

• Caused by: corrosion (acid-like character of the chlorine in the seawater), hydraulic action (wave pressure), abrasion (grinding of particle on particle).

Wave-Cut Platforms and Associated Landforms

• Origin: natural result of erosion on solid bedrock.
• Formation of: headlands, sea arches, sea stacks
• Straightening of coasts caused by refraction of wave energy on headlands causing them to be eroded more rapidly while intervening bays will up.

Types of Coasts

• submergent vs emergent

Submergent

• drowned, land down (or sea level up): Chesapeake Bay

Emergent

• tectonic uplift (like the southern California coast) or isostatic rebound (like coasts of Ireland and Baltic region).
• marine terraces

Tides

• Caused by gravitational forces of the sun and moon.
• Terms: spring vs neap tides
• Tidal ranges vary tremendously around the world - function of bottom shape, continental shelf topography, currents