Geology 104 - Spring 2007
Lecture #24

Cape Hatteras and Padre Island National Seashorses

Coastal Plain Province

General characteristics

• Rises from sea level to several hundred feet
• Descends seaward to submerged continental shelf

Barrier islands

1. Description

• Def: offshore sand bar that rises above sea level
• No rocks
• Protects land from storms

2. Processes of formation

• During Ice Age, sea level was lower.
• Sand accumulated on today's continental shelf
• After ice age rising water submerged the beaches.
• Longshore drift = process that carries sand parallel to shoreline.
• Sand dunes and barrier islands are dynamic.
• shore

Cape Hatteras NS

A. Topography and history

• Located in North Carolina along the Atlantic Ocean
• NS - 1937

Dunes may be stabilized artificially by a variety of structures:

• Groin = stone wall perpendicular to shore
• Jetties = pair of walls built to protect harbor
• Breakwater = wall parallel to shoreline
• All affect longshore drift of sediment
• Changes occur in both deposition and erosion

Cape Hatteras Lighthouse

• Built 1870
  • Built 1500 ft from sea, now 160 ft from sea
  • If sea level rises 2 inches, beach in front of the lighthouse would shrink by 150 feet .
  • So in 1999, lighthouse was moved 2900 ft inshore

Padre Island NS

• Located in Texas along the Gulf of Mexico
• NS 1962
• Longest continuous national sea (65 miles of beach along Gulf Coast)

Topography

• East side: beach
  • Mostly hard-packed sand
  • Middle section shelly
• West of beach is dune ridge
  • Runs length of island
  • Up to 50 ft high
• West side: lagoon
  • Shallow, very salty
  • Mudflats
  • Access restricted because of environmental sensitivity

Formation

• Began ~4500 y.a. (14C dating of shells)
• Island was formed by 3000 y.a.
• Grew by longshore drift
• Three stages:
  • Accretionay stage (building - complete)
  • Equilibrium stage (northern half)
  • Erosional stage (southern half)

Critical habitat for green sea turtles

Cape Hatteras slides

Padre Island slides

Please report any problems to herrstro@uiuc.edu.