Tectonic Plates and Plate Boundaries

• Tectonic plates are large sections of Earth's lithosphere, or crust, that interact in various ways.

Tectonic Plates

• Tectonic plates are large slabs of the Earth's crust that move freely on currents in the liquid mantel beneath the lithosphere
• The mantle is the portion of the Earth that is molten rock.
• Liquid magma heats up as it moves closer to the Earth's core, becomes less dense, and rises.
• Magma cools at the surface and sinks again, creating convection currents that cause tectonic plate movement.
• Continental and oceanic are the two main types of tectonic plates, differentiated by composition, not location.
• Continental plates are lighter and less dense, composed of granite rocks made of quartz and feldspar
• Oceanic plates are denser and heavier, composed of basaltic rocks.

Plate Boundaries

• Plate boundaries are the ways that tectonic plates interact with each other.
• Convergent, divergent, and transform are the three main types of boundaries.

Convergent Boundaries

• A convergent plate boundary is where two plates collide
• Convergent boundaries can occur between oceanic and continental plates, or between two of the same plates.
• When a continental and oceanic plate collide, the denser oceanic plate subducts (sinks) under the continental plate.
• When two oceanic plates collide at a convergent boundary, one will sink under the other.
• When two continental plates collide, they are both pushed upward to form large mountain ranges.
• The collision of the India Plate with the Eurasian Plate, forming the Himalayan mountains, is an example of a convergent boundary.

Landforms of Convergent Boundaries

• Mountains, volcanoes, and subduction zones with large trenches can form from convergent boundaries.
• The collision of two plates can push crusts together, forming mountain ranges like the Himalayas.
• Convergent boundaries between oceanic and continental plates have a subduction zone.
• Magma can escape through the lithosphere at a subduction zone, forming volcanoes and mountains.
• Volcanic mountain ranges like the Cascades or the Andes are formed this way.
• Subduction zones can also form large trenches like the Mariana Trench, and volcanic islands like the Aleutian Islands.

Divergent Plate Boundaries

• Divergent plate boundaries occur when two plates separate from each other.
• The Mid Atlantic Ridge is the largest underwater mountain range, formed by a divergent plate boundary.

Landforms of Divergent Boundaries

• Rift valleys, oceanic trenches, and underwater mountain ranges are created from divergent plate boundaries.
• At a divergent boundary, two plates move apart and new magma rises, creating new crust.
• The Mid Atlantic Ridge is a divergent plate boundary spanning the Atlantic Ocean.
• Magma released into the ocean at the Mid Atlantic Ridge forms a large mountain chain.
• The East Africa Rift Valley is formed where the Somalian plate moves away from the Nubian plate.
• Extension of the crust in the East Africa Rift Valley region forms lowland valleys with steep faults.

Transform Plate Boundaries

• Transform boundaries are areas where two plates slide past each other.
• The San Andreas Fault in California is a well-known transform boundary.

Landforms of Transform Boundaries

• Transform boundaries create fault lines, where plates slide past each other horizontally and cause rock to fracture.
• Pressure builds up behind plates at fault lines, rock is smashed, and energy is released as earthquakes.
• Normal, reverse, strike-slip and oblique are types of fault lines created by transform boundaries.
• In a normal fault, the higher rock moves down.
• In a reverse fault, the lower rock moves up.
• In a strike-slip fault, the plates move horizontally past each other.
• Oblique faults have movement that cannot be classified completely as any of the other faults, but is in the strike-slip plane along with normal or reverse movement.
• The San Andreas Fault is a strike-slip fault between the Pacific and North American plates.
• The movement of the plates sliding past each other at the San Andreas Fault has caused many earthquakes in California.

Convergent vs. Divergent Boundaries

• Convergent boundaries have plates that move towards each other, while divergent boundaries have plates that move away from each other.
• Mountains and volcanoes can be created by both convergent and divergent boundaries, although the geology of how these features form is different.

An overview of tectonic plates, their movement, and the different types of plate boundaries. Tectonic plates consist of the Earth's crust that move due to convection currents in the mantle. The three main types of plate boundaries are convergent, divergent, and transform.