1. Accretional (Depositional) Coastal Features
Spits
Tied to the coast at one end
Fundamental in smoothing an irregular coastline
Often exhibit a “recurved” hook at the downdrift end
Netarts Spit, Oregon

2. Examples of Spit Growth
Geomorphic history of Fire Island, NY - from aerial photography - growth in direction of L.S.T.
Older hooks reflect paleo- spit ends
Spit growth can deflect the course of a river

3. Google Earth Exercise - Go Spit Hunting

4. Tombolos Occur where spit growth extends to an offshore island
Island often influences wave field - refraction
Italian term, where they are numerous and well-developed
see Figure 2.16 in Komar

5. Cuspate Forelands / Capes
World class example: Outer Banks, NC
Mechanism of formation is debated:
1. Form at points of LST convergence from 2 directions?
2. May have a geologic control?

6. Barrier Islands Occur along 13 % of the world’s shorlines
Prevalent in areas of small tidal range = 1-2 meters

7. Blackboard Example: barrier island migration
set up slope of substrate, rate of sea level rise, retreat rate of barrier island
washover mechanics

8. Washover of Barrier Islands

9. Regressive vs. Transgressive Sequences
Rooted in Walther’s Law
Regressive Sequence - Landward sediments are deposited on top of seaward seds, reflect a seaward shift of shoreline.
Transgressive Sequence - Seaward sediments are deposited on top of landward seds, reflect a landward shift of shoreline.
Not necessarily diagnostic of SL rise or fall - think about sediment supply.

10. Theories of Barrier Island Formation
Hoyt (1967) - sand dunes drowned in place by relative SL rise
de Beaumont (1845) - cross-shore sed. transport, from an excess, “traps” a lagoon.
Gilbert (1885) - Longshore sediment transport downdrift of a headland, or inlet, forms spits, that are occasionally breached.
(aside on inlets, tidal prisms, and ebb tidal deltas)
3 “models” not mutually exclusive - D.J.P. Swift (1968)

11. Inlet Dynamics: Spit Growth to Equilibrium Length
Thought to be controlled, in part, by tidal prism:
Within each tidal cycle, a “prism” of water must be moved into, and out of, the bay.
Spit extends freely until tidal currents, through narrowing inlet, disallow longshore transport - tidal currents generate shear stress sufficient to block longshore sediment transport.
Sediment “sinks” are the flood tidal and ebb tidal shoals (deltas)

12. Inlet Spacing Related to sediment supply / distance from source
Near the sediment source (eroding headland, river mouth, etc.), inlet spacing is wide.
Flood and ebb-tidal shoals are a net sink for sediment, LST rate decreases downdrift.
At the distal end of the barrier island system (relative to source), inlet spacing becomes close, due to decreased LST rate

13. Beach Ridge Sets
Ubiquitous Landforms, without a clear explanation of their formation, preservation, and evolution.
One clear requirement – sediment supply.
Rink & Forrest (2005) combined OSL dating with Brooks (1972) RC dates to establish land accretion rate from beach ridges to be ~135 m/century
Examine numerous beach ridge sets through google earth.

14. Beach Ridge Generation by Changes in Wave Climate & Sediment Supply
St. Vincent Island, Apalachicola Delta, FL