Transcript Continental Margins: Active vs. Passive

Continental Margins:
Active vs. Passive
Different Continental Margins
Active vs. Passive
► There
are two types of margins:
 Active (Pacific-type)
 Passive (Atlantic-type)
► Both
are influenced by the process of plate
tectonics such as:
 Erosion, deposition, uplift and subsidence
► Also
influenced by climatic changes such as
sea level rise and fall due to changing ice
caps.
Active Continental Margin
Passive Continental Margin
Active Margins
► Located
near or adjacent to a plate
boundary.
► Earthquakes & volcanic activity.
► Most commonly a subduction zone.
► Dominated by erosional features as
shoreline is retreating landward.
► Narrow continental shelf, steep continental
slope, and continental rise is commonly
absent.
► Sediment poor; falls in trenches
Active Margins
Active Margins – Erosional Features
Erosional coasts with cliffs
and narrow beaches.
Big Sur, Central California
Active Margins – Erosional Features
Sea Stacks & Sea Arches
Cabo San Lucas
Pocket Beaches
Features show
where land “used”
to be. Terraces
show ancient
shorelines.
Marine Terraces of San Clemente Island
Active Margins – Landslides
Passive Margins
► Located
far from active plate boundaries.
► Continental margins usually surround an
active spreading center.
► Dominated by depositional features as
shoreline is building outward.
► Wide continental shelf, moderate continental
slope, and a well developed continental rise.
► Sediment-rich
Passive Margins
Passive Margin – Depositional Features
Chesapeake Bay
shows drowned
valleys, capes, and
barrier islands.
Cape
Sediment from the
continent is building
outward, not
eroding.
Passive Margin – Depositional
Features
Barrier Islands
Capes (Cape Cod)
River Deltas
Barrier Island – Manhattan Island
Passive Margin – Beaches
Wide beaches that are
very flat. No cliffs.
Lots of sediment!!!
Passive Margin – Hazards
Barrier Island before hurricane Ivan and after hurricane
Ivan. A lighthouse is shown in the box.
Passive Margin – Hazards
Climate change is causing the ice caps to melt. If they
completely melt, this is what will happen to passive
continental margins.