Plate Interactions Plate Boundaries Plate Boundaries Region where

Plate Interactions (Plate Boundaries)

Plate Boundaries • Region where two tectonics plates are in contact.

Plate Boundaries • Plate boundaries are marked by geological features: • earthquakes, • volcanoes, • mountain ranges and • ocean trenches

There are three main types of plate boundaries: 1. Divergent 2. Convergent 3. Transform or Sliding

1) Divergent Boundaries (or Spreading Centers) • Where plates spread apart; • As lava surfaces, new crust is formed.

Divergent Boundaries Characterized by: Ocean ridges, (in oceans) eg. Mid-Atlantic Ridge

Divergent Boundaries characterized by: Sea floor spreading Eg. Endeavour hydrothermal vents were created as the Juan de Fuca plate moves away from the Pacific plate

Diverging Boundaries characterized by: • (on land) Continental Rifts – when spreading centers develop within a continent, the landmass may split into two or more smaller segments, forming a rift. Eg. East African Rift are slowly breaking Africa into pieces.

What Geological event/features occur at Divergent Boundaries? • Submarine mountain range eg. Mid-Atlantic Ridge; • volcanic activity in the form of fissure eruptions; • creation of new seafloor and a widening ocean basin. • shallow earthquake activity;

2. CONVERGENT BOUNDARIES • Where two plates collide • Denser crust eventually goes below the less-dense crust (subduction), • variable results depending on the plates involved… 3 types

a) Continental-Oceanic Plates • the oceanic plate subducts. • Continental crust never subducts because it is less dense than oceanic crust.

Features • Ocean Trenches • Sometimes volcanoes --> Volcanic Island Arcs

Features • Eg. • Andes Mountain Range, • Cascade Mountain Range, • Sierra Nevada Mountains.

• Mountain you may know in the Cascade Mountain Range: • Mount Garibaldi • Mount Meager

Correct your notes: • Mariana Trench belongs in Oceanic – Oceanic Boundary

We live near a subduction zone: Juan de Fuca Plate is sliding under North America Plate

B) OCEANIC-OCEANIC CONVERGENT BOUNDARY • When two oceanic plates collide, usually older, more dense plate subducts beneath the other.

B) OCEANIC-OCEANIC CONVERGENT BOUNDARY • Features: • Mountains on ocean floor. • Volcanic Island Arcs above the non-subducting plates • Eg. Islands of Japan and Indonesia • Eg. Aleutian Island of Alaska • Ocean trenches eg. Mariana Trench • Deep Earthquakes

Oceanic-Oceanic Plates- Features • Volcanoes on ocean floor • Volcanic Island Arcs form above the non-subducting plate. • Eg. Japan, Indonesia • Ocean Trenches • Deep Earthquakes

Eg. Aleutian Islands of Alaska

Ocean Trenches: eg. Mariana Trench: the deepest known point in Earth's oceans. 10, 994 meters below sea level

c) Continental-Continental Plate Convergence • Neither plate is dense enough to be pushed down, so the land buckles like a car hood in a car crash (“uplifting”),

c) Continental-Continental Plate Features • Mountain Ranges • Eg. Himalayas formed from Indian continent colliding with Asian continent. • Youngest and highest mountain range • Continue to increase in elevation by several cm per year

3) Transform Boundaries • Where two plates grind past each other without destroying the lithosphere. • Results in frequent earthquakes and faults (fracture in the crust) • No mountains or volcanoes

3) Transform Boundaries • Mostly occur near ocean ridges • Eg. Oct 2012, an earthquake of magnitude of 7. 7 originated from movement along the Queen Charlotte Fault.

Transform Boundary • Eg. San Andreas Fault, California

All 3 types of plate boundaries exist in BC •

Plate Boundary Symbols

Pacific Ring of Fire • Major area in the basin of the Pacific Ocean where ~ 90% of earthquakes and ~ 75% of all active volcanic eruptions occur

Check your Understanding 1. Be able to name and draw three main types of tectonic plate boundaries. 2. Be able to name events or land formations that occur at each boundary, and give an example of each. 3. Why does subduction not occur at some kinds of tectonic plate boundaries? 4. Describe the process that results in a volcanic island arc. 5. What types of boundaries do we live near?

Practice • Part D: Last two pages of Plate Tectonic package • Bring textbook next class for mapping activity. • Use notes, Plate Tect package and Study Guide to study for Plate Tectonic Quiz Feb 14/18.