Lecture 15:  Where Sea Meets Land – Coastlines, Beaches & Sea Level
Focus Question:  Why do coastlines change?

Readings:  Ch. 12, pgs. 315-327 (Ch. 12, pgs 275-286)

This is a text version of the notes presented in class.

Feel free to email the instructor (knamjesn@kent.edu) with any
comments about the format and ease of use of these online notes.

1. Where Sea Meets Land -  Coastlines, Beaches & Sea Level
- Coasts
- Beaches
- Sea Level  

2. The Dynamic Coastline
Coasts are regions of constant and sometimes rapid change

3.  Sea Level Changes through Time
 Sea Level has been rising very slightly but steadily throughout the 20th century, about 1 to 2 mm/year.  This is part of a general rise in sea level since the close of the last ice age, when the continental glaciers started melting, returning water to the sea.  The general rate of sea level rise since the end of the last ice age has varied, but has risen
 about 9 meters in the past 7,000 years.

4.  Global Sea Level Change may not be the same as local or regional sea level change.
Global Sea Level is an average value, and is strongly affected by the presence of ice on the continents, sea floor spreading rates, and global warming or cooling.
 Local/Regional sea level change can be different from Global Sea Level Change, because
 Coastland may be rising or sinking due to changes in
 Compaction/collapse of local coastal areas due to groundwater pumping
 Erosion or deposition, resulting in loss or development of coastal area

5.  Future projections for sea level rise are conservative (about 2 meter rise this 21st century).  However, large populations of the world live within 2 meters of sea level now.

6.  Characteristics of Coasts
The location of a coast depends on sea level, which changes through time
The shape of a coast depends on:
- uplift and subsidence
- erosion
- the redistribution of material by sediment transport
Graphic: Garrison, Fig. 12.2 pg. 318 (Fig.12.1, pg 277).

7. Classification of Coasts
Erosional coasts:
 Land-based influences determine the form of the coast
 Relatively "young", rough and irregular   

Depositional coasts
 Heavily influenced by marine processes
 Usually older than primary coasts

8. Erosional Coasts
Processes that shape primary coasts:
- Land erosion
- Land processes (sediment deposition, glacial deposits)
- Volcanic activity
- Earth movements 

9. Depositional Coasts
Processes that shape secondary coasts:
- Waves and currents
- Stream erosion
- Abrasion of wind-driven particles
- Freeze/thaw cycles
- Slumping
Graphic: Garrison, Fig. 12.26, pg. 334, (Fig. 12.25, pg. 292).

10. Shaping an Erosional Coast - Wave Energy
Wave energy converges on headlands and diverges in bays
   this tends to straighten shorelines over time
Graphic: Garrison Fig. 12.4, pg 319 (Fig. 12. 3, pg. 279).

11. Shaping a Depositional Coast -  Sediment Transport
Longshore drift = movement of sand along a beach by wave action
Graphic: Garrison Fig. 12.16, pg 326 (Fig. 12.15, pg. 285).

12. Coastal Cells
Regions where sand input and outflow are balanced
Sand moves in to a cell via rivers and longshore drift
Sand is removed from a cell when it is transported offshore
Graphic: Garrison, Fig. 12.18 pg. 328 (Fig. 12.17, pg 297).

13. Features of Depositional Coasts
Graphic: Garrison, Fig. 12.19, pg. 329, (Fig. 12.18, pg 287).

14. Beach Shape
Graphic: Garrison Fig. 12.14, pg 325, (Fig. 12.12, pg. 283)

15. Beach Composition and Slope (see graphical version of notes for accurate
reproduction of this table)
The slope of a beach depends on particle size
Type of Material   Size (mm)   Average Beach Slope
Fine sand        0.125-0.25         3°
Medium sand     0.25-0.5          5°
Coarse sand       0.5-1.0           7°
Pebbles              4-64             17°
Cobbles           64-256           24°

16. Long-Shore Drift - An Example
Sand accumulates "upstream" of the barrier
Sand is depleted and erosion is accelerated "downstream" of the barrier

17.  Ancient Harbors, Dynamic Coastlines, and Archaeology
 Ancient city of Troy (subject of Homer’s Iliad) located near the Scamander River in Turkey, sediment transport from the river and longshore drift along the coastline have resulted in the ancient site now being located far inland from the sea.

Leptis Magna Harbor on the North African Coast of the Mediterranean, was abandoned in Roman times because of silting-in.

18. U.S. Coasts
Pacific Coast:
 Beaches interrupted by rocky headlands
 Rivers are the main source of sand
Atlantic Coast:
 Deep sediments offshore are the main
  source of sand
Gulf Coast:
 Less wave energy and small tidal range
 Large deltas and barrier islands

19. Coastal Erosion
Coastal erosion varies from place to place, depending on
- hardness and resistance of rock
- wave action
- local range of tides
Graphic: Garrison, Fig. 12.38, pg. 343, (Fig. 12.36, pg. 300).

Next Lecture:
Coasts and Real Estate
Ch. 327-346, (Ch. 12, pgs. 286-303)
Focus Question:  How does coastal change impact real estate?