Science Review Activity

Abhinav Vetcha pd.5 Mr.Mckenna

Tectonic Plates

The tectonic plates are parts of the lithosphere that move around and interact with each other on top of the asthenosphere. They are like jigsaw puzzles and fit together to form the Earth's crust.

These are the major tectonic plates of Earth.


Plate tectonics
is the theory that the Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere.


There are three types of interactions between plates: Divergent, Transform, & Convergent


Divergent Boundaries

In divergent boundaries, plates move apart from each other, forming mid-ocean ridges or rift valleys. Some of the features of a divergent boundary are volcanoes and trenches. Some examples of divergent boundaries are the Mid-Atlantic Ridge and the East Africa Rift in Kenya.


Transform Boundary

A Transform Boundary is a place where two plates rub against each other without directly colliding. There are no features formed during this type of collision but there is major lateral damage to the plates in the collision. Some world examples are the San Andreas fault in California and the Alpine fault in New Zealand.


Convergent Boundary

There are three types of convergent boundaries that are classified by the type of plates that are colliding. The three types are Continental-Continental, Continental-Oceanic, and Oceanic-Oceanic. Subduction is the process by which one lithospheric plate moves beneath another as a result of tectonic forces.

Continental-Continental Boundary

In a continental to continental convergent boundary the continents on either side of the boundary collide and both continents are forced upward. The features formed in this type of boundary are mountains and earthquakes. A world examples of this boundary are the boundary between the subcontinent of India and the continent of Asia whose collision formed the Himalayan Mountains.

Continental-Oceanic Boundary

In Continental to Oceanic boundaries an Oceanic plate is colliding with a Continental plate. Because of its greater density, the Oceanic plate goes under the continental plate and gets recycled by the mantle of the Earth. Some of the features formed because of this kind of boundary are trenches, earthquakes, and volcanic arcs. Some world examples are the Cascades Mountain range and the trench near Chile and Peru because of the collision of the South American Plate which is a continental plate and the Nazca Plate which is an oceanic plate.

Oceanic-Oceanic Boundary

In Oceanic to Oceanic boundaries, two Oceanic plates are colliding. One of the oceanic plates goes under the other one. The features formed by this type of boundary are trenches, earthquakes, and a volcanic island chain. Some world examples are the collision that formed Japan and the collision that formed the Aleutian islands.

Juan De Fuca

The Juan De Fuca region is the region of Upper California, Oregon, Washington, and a small part of Southwest Canada. The area has a Triple Junction. A Triple Junction is a region where all three types of plate collisions are occurring. There are many volcanic mountains in the Northwest part of the United States because of a convergent boundary between the Juan De Fuca plate and the North American plate.

Volcanic Eruptions


Types of Eruptions

Non-Explosive Eruptions

Non-Explosive eruptions are the more common type and they produce relatively calm flows of lava. They can spew out lots of lava and the lava covers a lot of the world's land and most of the Northwest region of the United States.

Explosive Eruptions

Explosive eruptions are less common and can be very devastating. Clouds of hot debris, ash, and gas rapidly shoot out from a volcano during the eruption. Instead of lava flows, bits of molten rock can shoot up into the air and ash can circle the Earth for years. A volcano can destroy itself during an explosive eruption.

Why Explosive Eruptions Occur

Explosive eruptions occur mainly for two reasons. One is because of high water content in the magma. Because of the pressure underground the water stays dissolved but when the magma rushes to the surface, the pressure decreases and the water and other compounds such as carbon dioxide becomes gases. As the gases expand, the pressure builds up and the volcano erupts explosively like a soda bottle that has been shaken and the cap opened. High silica content also leads to an explosive eruption. As silica-rich magma tends to have a higher consistency, it plugs up the vent of the volcano. Because of this, pressure builds up until the magma bursts out of the volcano violently.

Types of Lava

Aa lava

It comes out quickly and forms a brittle crust that gets cut into smaller bits as lava flows underneath it.

Pahoehoe lava

Pahoehoe lava has a high viscosity and flows slowly. Its glassy surface has rounded wrinkles.

Pillow lava

Pillow lava is lava that forms underwater in pillow shaped clumps.

Blocky Lava

Blocky lava is cool and stiff lava that forms sharp-edged chunks of rock.

Types of Volcanoes

Shield Volcano

A shield volcano has a wide base and gentle slope. It has a gentle slope because of the mafic lava which makes it. Since mafic lava is runny. It comes out quickly and calmly to make a gentle slope. Shield volcanoes do not explode because of the type of lava they erupt. This lava is not stiff so it comes out of the volcano without an explosion. The type of eruption is lava flow. Most shield volcanoes occur on divergent boundaries. Some world examples are Mauna Kea in Hawaii and the Erta Ale in Ethiopia.

Cinder Cone Volcano

Cinder cone volcanoes are short volcanoes that also last for only a short time. Unlike shield volcanoes, cinder cones are steep and erupt felsic magma. Felsic magma is a stiff type of magma so it explodes out of a volcano. A cinder cone's type of eruption is pyroclastic material because of the type of magma. The felsic magma plugs up the vents and builds up pressure, and after the pressure is too much the magma explodes from the volcano. Some world examples of cinder cone volcanoes are Paricutin in Mexico and the Taal volcano in the Philippines.

Composite Volcano

Composite volcanoes are like cinder cone volcanoes and shield volcanoes combined. Composite volcanoes alternate between calm lava flows and explosive pyroclastic material. Composite volcanoes are made of alternate layers of both types of magma. They are steep and also have a wide base. Some world examples of composite volcanoes are Mt.Fuji in Japan and Krakatoa in Indonesia.

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