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Describe the geological changes and events that occur at convergent, divergent, and transform plate boundaries.

Plate Tectonics

The idea that Earth’s lithosphere is divided into plates is known as plate tectonics.

These plates are like puzzle pieces in constant motion, sliding around by floating on the top layer of the mantle, known as the asthenosphere.

Continental plates lie beneath landmasses and oceanic plates lie beneath the oceans. Movement of the plates produces mountains, volcanoes, the oceanic ridge system, undersea trenches, and other physical features on Earth. Earthquakes and volcanoes are not randomly distributed across the globe. These occur along plate boundaries (fault lines).

Watch the video below to learn more about how we know where the plates are located based on historical earthquakes and volcanic eruptions:

Essential Knowledge

Maps that show the global distribution of plate boundaries can be used to determine the location of volcanoes, island arcs, earthquakes, hot spots, and faults.

Types of Plate Boundaries

Tectonic plates meet each other in one of three ways: convergent, divergent, or transform boundaries. As divergent boundaries create new crust, convergent boundaries must crush crust because the diameter of the Earth does not change.

The three types of plate boundaries — **Convergent boundaries often occur along oceanic trenches and subduction zones. Divergent boundaries occur in locations of seafloor spreading. Transform boundaries slide against one another.**

Explore the tabs below. Have you ever experienced an earthquake? Do you have a favorite plate boundary? (I do - divergent boundaries because I think seafloor spreading is neat - new crust! - and hydrothermal vents are incredibly interesting)

Convergent
Divergent
Transform

Convergent Boundaries

When plates crash into one another, it is known as a convergent boundary.

Convergent conversions are typically quite violent and shape the Earth’s surface and create geological features like trenches, mountains, and island chains. They can also cause earthquakes, tsunamis, and form volcanoes.

Convergent plate boundaries are also sites where new crust is created or destroyed, which affects the distribution of continents and oceans over time.

There are three ways plates can collide at convergent boundaries: continent-continent, continent-oceanic, oceanic-oceanic.

Explore the interactive on this tab to learn more about each type of convergent boundary collisions. Which type can cause earthquakes? Which cause trenches? Which plates are the heaviest?

Divergent Boundaries

divergent plate boundary with plates moving AWAY from each other — **Divergent plate boundaries are places where two tectonic plates move away from each other, creating new crust.**

Divergent plate boundaries are places where two tectonic plates move away from each other, creating new crust and widening the ocean basins. This happens because of the rising convection currents in the mantle that push up on the bottom of the lithosphere and cause it to split apart. Divergent plate boundaries can occur both in the ocean and on land, creating different features.

On land, divergent plate boundaries form rift valleys, which are long, narrow depressions where the continental crust is stretched and thinned. An example of this is the East African Rift, which splits the African plate into two smaller plates: the Somali Plate and the Nubian Plate. As the rift widens, streams and lakes fill the valley, and volcanoes and hot springs dot the landscape.

In the ocean, divergent plate boundaries form mid-ocean ridges, which are underwater mountain ranges where magma rises and solidifies as new seafloor.

Hydrothermal vent on ocean floor - is a fissure in Earth’s crust that releases hot water and minerals. — Hydrothermal vents are openings on the seafloor where hot, mineral-rich water gushes out of the opening. They form near volcanic activity and support diverse life forms that rely on chemical energy, instead of the sun.

When this type of boundary occurs between oceanic plates, it is known as seafloor spreading, which causes rising magma to form new oceanic crust on the seafloor at those boundaries. This is one way that important elements, such as copper, lead, and silver are brought to the surface of the Earth from the inner layers.

An example of this is the Mid-Atlantic Ridge, which separates the North American and Eurasian plates in the north, and the South American and African plates in the south.

Divergent plate boundaries shape the Earth’s surface and create new crust and affect the distribution of continents and oceans over time, as they cause the continents to drift apart or collide. Divergent plate boundaries are also sites where life can thrive, as the hydrothermal vents along the mid-ocean ridges provide energy and nutrients for diverse organisms.

Transform Boundaries

transform plate boundary with plates moving AGAINST each other — **Transform fault boundaries are often responsible for earthquakes.**

When two plates slide beside each other, it is known as a transform fault boundary. These plates often stick together because plates are not well lubricated, so there is a lot of friction between the two plates.

When these plates move, they can create huge earthquakes. These "fault lines" are zones of weakness where the crust can break and release energy. The energy travels as seismic waves that shake the ground and anything on it.

An earthquake can happen anywhere, but they are most common and intense in areas near tectonic plate boundaries.

Earthquakes can cause additional national disasters, such as tsunamis and landslides. They can also pose risks and challenges for human activities, such as agriculture, industry, infrastructure, and urban planning.

The San Andreas Fault in California is a famous transform fault boundary known for its seismic activities, where tectonic plates slide past each other.

These boundary types are notorious for causing earthquakes, making the region a hotspot for geological studies and monitoring.

The image depicts a map of California and its surroundings, showing plate boundaries and faults. The San Andreas Fault, a transform boundary, runs along California's western edge, dividing the Pacific and North American Plates. — **Transform fault boundaries are often responsible for earthquakes.**

Despite its reputation for seismic activity, it's important to note that California will not simply "fall into the sea," contrary to popular belief.

Situated between the Pacific and North American plates, California experiences a unique geological phenomenon. Southern California is gradually shifting towards Alaska on the Pacific Plate, while northern California moves southward on the North American Plate. This movement creates a division in the state, highlighting the dynamic nature of Earth's tectonic plates.

Despite its reputation for seismic activity, it's important to note that California will not simply "fall into the sea," contrary to popular belief.

Essential Knowledge

Convergent boundaries can result in the creation of mountains, island arcs, earthquakes, and volcanoes.

Divergent Boundaries can result in seafloor spreading, rift valleys, volcanoes, and earthquakes.

Transform boundaries can result in earthquakes.

An earthquake occurs when stress overcomes a locked fault, releasing stored energy.

AP Exam Tip

As divergent plate boundaries create new crust, convergent boundaries must crush crust, as the Earth's diameter does not noticeably change.

You should know the difference between convergent, divergent, and transform boundaries and the importance of each.

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