Plate boundaries and Tectonic processes
DIVERGENT BOUNDARIES:
PLATES MOVE APART: Seafloor spreading
• Creates ridge-rift systems and new seafloor
• MID ATLANTIC RIDGE and GREAT AFRICAN RIFT VALLEY are examples
CONVERGENT BOUNDARIES
• PLATES MOVE TOGETHER & COLLIDE
• WHAT HAPPENS DEPENDS ON DENSITY:
– Equal density – two continental plates – FOLDING (mountains)
– Different densities – denser plate sinks – SUBDUCTION:
• OCEAN – OCEAN PLATES : ISLAND ARCS
• OCEAN – CONT. PLATES: VOLCANIC ISLAND CHAINS
Since plates are of equal density – neither sinks –
both buckle upwards – process of FOLDING produces
FOLDED MOUNTAINS (Appalachians, Himalayas)
CONVERGENT BOUNDARY–
2 CONTINENTAL PLATES: FOLDING
CONVERGENT - SUBDUCTION
Denser plate edge (oceanic) sinks into
asthenosphere, is melted, and creates VOLCANIC
MOUNTAIN RANGES (Cascades, Andes, Sierra Madres)
Ocean – ocean plate subduction
Older and denser plate edge (left) is subducted under
younger / less dense plate (right). This forms VOLCANIC ISLAND ARCS (Aleutians, Japan, Indonesia)
MAJOR EARTHQUAKE AND VOLCANO
ZONES EXPLAINED- They occur along
PLATE BOUNDARIES!
CONVERGENT - THE RING
OF FIRE - SUBDUCTION
DIVERGENT: MID-ATLANTIC
RIDGE – SEAFLOOR
SPREADING
HOT SPOTS – “Volcanic exceptions” –
occur in middle of plates
CLICK HERE TO VIEW ANIMATION
Formation of the Hawaiian Islands