Discuss different types of plate boundaries and enumerate their characteristic features.

Convergent Plate Boundaries

Convergent boundaries occur where two plates collide. The outcome of this collision depends on the types of plates involved – oceanic-oceanic, oceanic-continental, or continental-continental.

Oceanic-Oceanic Convergence

• One oceanic plate subducts (slides) beneath the other.
• This process forms a deep-sea trench, volcanic island arcs (e.g., Japan, Aleutian Islands), and frequent earthquakes.
• Partial melting of the subducting plate generates magma, leading to volcanism.

Oceanic-Continental Convergence

• The denser oceanic plate subducts beneath the less dense continental plate.
• This creates a volcanic mountain range on the continent (e.g., Andes Mountains), a deep-sea trench offshore, and a zone of intense earthquake activity.
• The subduction process also leads to metamorphism of the continental crust.

Continental-Continental Convergence

• Neither plate readily subducts due to similar densities.
• This results in a collision zone, forming large, non-volcanic mountain ranges (e.g., Himalayas, Alps).
• Intense folding and faulting of the crust characterize these zones, along with widespread earthquakes.

Divergent Plate Boundaries

Divergent boundaries are where two plates move apart. This typically occurs at mid-ocean ridges.

• Magma rises from the mantle to fill the gap, creating new oceanic crust (seafloor spreading).
• This process forms mid-ocean ridges (e.g., Mid-Atlantic Ridge), rift valleys, and shallow-focus earthquakes.
• Volcanic activity is common, but generally less explosive than at convergent boundaries.
• Continental rifting can also occur, eventually leading to the formation of a new ocean basin (e.g., East African Rift Valley).

Transform Plate Boundaries

Transform boundaries occur where two plates slide horizontally past each other.

• These boundaries are characterized by frequent, shallow-focus earthquakes.
• No new crust is created or destroyed.
• Transform faults often offset mid-ocean ridges (e.g., Fracture Zone along the Mid-Atlantic Ridge) or connect other types of plate boundaries.
• A well-known example is the San Andreas Fault in California.

Plate Boundary Type	Characteristics	Examples
Convergent (Oceanic-Oceanic)	Subduction, trenches, volcanic island arcs, earthquakes	Japan, Philippines
Convergent (Oceanic-Continental)	Subduction, volcanic mountain ranges, trenches, earthquakes	Andes Mountains, Cascade Range
Convergent (Continental-Continental)	Collision, mountain building, earthquakes	Himalayas, Alps
Divergent	Seafloor spreading, mid-ocean ridges, rift valleys, volcanism, earthquakes	Mid-Atlantic Ridge, East African Rift Valley
Transform	Horizontal sliding, earthquakes	San Andreas Fault

It's important to note that plate boundaries are not always simple, well-defined features. Some areas exhibit complex interactions involving multiple plate boundaries or intraplate deformation.