Tectonic Plates Plate Boundaries and Plate Boundaries

I. Tectonic Plates A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock.

* Earthquakes *Mountain building Tectonic Plates The movement of tectonic plates result in major geological events, such as: * Earthquakes *Mountain building *Volcanic eruptions *Sea-floor spreading

Tectonic Plates Some changes in the earth’s surface are abrupt (such as earthquakes and volcanic eruptions). Other changes are gradual (such as uplift and wearing down of mountains).

Tectonic Plates Tectonic Plates are in constant motion. Most of the motion occurs at plate boundaries (where two plates meet). Tectonic Plates move in response to convection currents in the mantle.

Tectonic Plates Because of the movement of tectonic plates, Earth’s crust is constantly being recycled (being built up and torn down).

II. Tectonic Plate Boundaries A tectonic plate boundary(also called a fault) occurs where two tectonic plates meet.

Tectonic Plate Boundaries There are 3 types of boundaries where tectonic plates meet.

Divergent Plate Boundary As plates pull apart, a crack in the ocean floor appears. Magma oozes up from the mantle to fill in the space between the plates, forming a raised ridge called a mid-ocean ridge.

Convection Currents

Divergent Plate Boundary At divergent plate boundaries such as the Mid-Atlantic Ridge, new ocean floor is created during sea-floor spreading.

Iceland vs. the Mid-Atlantic Ridge Iceland Plate Diving

Convergent Boundary Because oceanic and continental crusts have different compositions, they react differently when they collide.

Oceanic crust is more dense and thinner Continental crust is Convergent Boundary Recall that… Oceanic crust is more dense and thinner Continental crust is less dense and thicker

Convergent Boundary There are 3 types of plate collisions… The more dense tectonic plate is pulled under the less dense tectonic plate (subduction).

Oceanic Plate vs Continental Plate Convergent Boundary Oceanic Plate vs Continental Plate Result is a volcano.

Continental Plate vs Continental Plate Convergent Boundary Continental Plate vs Continental Plate Result is folded mountain ranges (ex. Appalachian Mountains)

Oceanic Plate vs Oceanic Plate Convergent Boundary Oceanic Plate vs Oceanic Plate Result is a deep ocean trench and/or a volcano

Challenger Deep What is ?

Transform Boundary Because tectonic plates are under constant stress, sometimes a sudden break in the crust occurs. When plates slide past one another, extreme friction causes vibrations that travel to earth’s surface. The result is an earthquake. The San Andreas Fault in California is a transform boundary.

Photo of the San Andreas Fault near Gorman, California, showing rocks of the Pacific Plate (gray rocks on the left side of the fault) and the North American Plate (tan rocks on the right side of the fault).

Hot Spots Only under special conditions (at hot spots along plate boundaries) does the mantle or crust melt to make magma, which may then rise to the surface to make a volcanic eruption.

III. Hot Spots The Hawaiian Islands were formed over hot spots in the Pacific Ocean.

IV. Ring of Fire The Ring of Fire is an area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur.

Ring of Fire The Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90% of all earthquakes occur along the Ring of Fire, and the ring is dotted with 75% of all active volcanoes on Earth.  The Ring of Fire isn’t quite a circular ring. It is shaped more like a 40,000-kilometer (25,000-mile) horseshoe.