Plate Tectonics and Earth’s Lithosphere Lecture

These flashcards review key points from the lecture on Earth’s lithosphere, plate tectonics, types of plate boundaries, and associated geologic features and hazards.

What layers compose Earth’s lithosphere?

The crust and the uppermost part of the mantle.

What is the outermost solid layer of Earth called?

The crust.

Which three rock types primarily make up Earth’s crust?

Sedimentary, metamorphic, and igneous rocks.

What are the average density and thickness range of the crust?

About 2.8 g/cm³ and 5–50 km thick.

Where is the crust thickest and where is it thinnest?

Thickest beneath relatively young mountains; thinnest along the ocean floor.

What does the theory of plate tectonics state?

Earth’s lithosphere is broken into slowly moving plates.

Approximately how many major tectonic plates are there?

About 15, with 7–8 primary (largest) plates.

Name the seven primary lithospheric plates.

African, Eurasian, Australian, North American, South American, Pacific, and Antarctic plates.

Is the Philippine Plate considered primary or secondary?

Secondary (smaller) plate.

List three geologic activities that commonly occur at plate boundaries.

Earthquakes, volcanic eruptions, and mountain‐range formation.

Define landforms.

Solid features of Earth’s crust such as mountains, volcanoes, valleys, islands, and canyons.

According to PHIVOLCS, when is a volcano considered active?

If it erupted in historical times, has documented eruptions, or erupted within the last 10,000 years.

How many volcanoes and active volcanoes are in the Philippines?

Over 200 volcanoes, 23 of which are active.

Which Philippine volcano has the most recorded eruptions?

Mayon Volcano in Albay (about 50 eruptions).

What is the Pacific Ring of Fire?

A 40,000 km horseshoe‐shaped zone around the Pacific Ocean with frequent earthquakes and volcanic activity, containing about half of the world’s volcanoes.

What do the red lines on seafloor maps usually represent?

Locations of underwater volcanoes along oceanic ridges.

Define an earthquake.

Vibration of Earth due to rapid release of energy.

Differentiate earthquake focus and epicenter.

Focus: point inside Earth where rupture starts; Epicenter: point on the surface directly above the focus.

Where do most earthquake epicenters and active volcanoes occur?

Along plate boundaries, especially the Pacific Ring of Fire and oceanic ridges.

What is a mountain belt (mountain range)?

A group of geographically related mountains formed by tectonic processes.

Give two major mountain ranges in the Philippines.

Sierra Madre and Cordillera ranges.

Why is studying plate boundaries important?

Because deformation and hazards such as earthquakes, tsunamis, and volcanic eruptions occur there.

At what typical speed do lithospheric plates move?

About 1–2 inches (3–5 cm) per year.

Describe a divergent plate boundary.

Two plates move apart, allowing magma to rise and create new crust.

Name two geologic features formed at divergent boundaries.

Oceanic ridges and rift valleys.

Describe a convergent plate boundary.

Two plates move toward each other, causing subduction or collision.

What are the three types of convergent interactions?

Oceanic–continental, oceanic–oceanic, and continental–continental convergence.

List four features produced at an oceanic–continental convergence.

Subduction zone, trench, continental volcanic arc, and earthquakes.

What forms at an oceanic–oceanic convergence?

Trench, volcanic island arc, and undersea earthquakes.

What major landform results from continental–continental convergence?

High mountain ranges (e.g., the Himalayas).

Define a subduction zone.

A region where one lithospheric plate bends and sinks beneath another into the mantle.

What is seafloor spreading?

Widening of the ocean floor as new crust forms at mid‐ocean ridges.

Describe a transform plate boundary.

Plates slide horizontally past one another, producing strike‐slip faults and earthquakes.

Provide a well‐known example of a transform fault boundary.

The San Andreas Fault in California, USA.

What are the main components of Earth’s lithosphere?

The crust and the rigid upper mantle.

How does continental crust differ from oceanic crust?

Continental crust is thicker, less dense, and granitic; oceanic crust is thinner, denser, and basaltic.

What is an oceanic trench?

The deepest part of the ocean floor formed at subduction zones.

Define a volcanic arc.

A chain of volcanoes that forms along the edge of a continental plate above a subduction zone.

What is a volcanic island arc?

A curved chain of volcanic islands that forms parallel to a trench in an oceanic–oceanic convergence.

Why is crust thick under relatively young mountains?

Compressional forces during mountain building shorten and thicken the crust.