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READ: Gallery — Geology

The features and physical processes of the Earth.

The Andes

© Maria Stenzel/National Geographic Society/Corbis
The Andes are the longest continental mountain range in the world, stretching about 7,000 km or 4,300 miles from the tip of Chile in the South to Ecuador, Columbia and Venezuela in the north. The highest peak in the Andes is Mt. Aconcagua (6,962 m/22,841 ft.) in Argentina. The Andes range contains numerous high plateau regions and helps feed  the Amazon River, the world's largest river by volume.

Folded Rock

Francois Gohier / Photo Researchers, Inc.
In this image of folded strata in the Andes north of Quito, Ecuador, the geologic processes that formed the mountains are clearly visible. When the oceanic crust of the Nazca plate "subducted" under the South American plate, the lighter continental crust crumpled and continued to push upwards, eventually forming the snow-capped Andes.

The Himalayas

© Olivier Matthys/epa/Corbis
Plate tectonics can also make mountains. Earth's biggest mountain range, the Himalayas formed when the India land mass (atop the Indian plate) slammed into the Eurasian plate. This slow motion collision happened about 50 million years ago, thrusting earth and stone skyward and forming many of the planet's highest mountains, including Mount Everest (8,848 m/29,029 ft.). Seen here are the Karakoram Mountains, a part of the Himalayas that spans the borders between Pakistan, India and China and includes K2 (8,611 m/28,251 ft.), the second highest peak in the world.


The Big History Project
In the early days of Earth, a process called differentiation separated our planet into distinct layers. Density was the key here. Heavier, denser metals like iron and nickel formed the Earth's core while the extremely tightly-packed rocky mantle (some of it molten) surrounded the core. The layer of lighter rock at the Earth's surface is called the crust. It's important to remember that the formation process and ongoing activity created areas where different materials mix, such as veins of metal that reach to the Earth's surface and volcanoes that pump molten lava from the Earth's mantle, sending ash and carbon dioxide into the atmosphere, Earth's outer, gaseous layer.

The Earth's Layers

The Big History Project
The Earth's iron-nickel inner core is hotter than the surface of the Sun but intense pressure makes it solid metal. Molten metal in the outer core generates the Earth's magnetic field and the intense heat sends convection currents into the rocky mantle. These currents, or seismic waves, move through the mantle, causing the movement of the Earth's tectonic plates. The crust, a relatively thin layer around the Earth (think of an apple skin), is composed primarily of basalt (in the oceanic crust) and granite (in the continental crust).

The Andes from Space

Jeff Schmaltz and NASA
In this image of the southern tip of South America, the snow-capped Andes Mountains are clearly visible along the western side of the continent. These mountains were formed when the heavieroceanic crust of the Nazca plate slipped under the South American plate, pushing the lighter continental crust upwards. As oceanic crust is pressed downward into the Earth's mantle, the "subduction zone" becomes a geologically active region, prone to both volcanoes and earthquakes.

Plate Tectonics

Wegener’s idea that the continents had moved was not accepted by the scientific community until more evidence was found. Geologist and naval officer Harry Hess used sonar readings of the ocean floor, some taken during World War II, to demonstrate "seafloor spreading," helping to cement the modern theory of plate tectonics. Now scientists know that the Earth’s crust consists of several interacting plates that fit together like a jigsaw puzzle. There can be intense pressure where two or more plates meet and these "plate boundaries" are responsible for most of the earthquakes and volcanoes on Earth.

Sarychev Peak Eruption in the Ring of Fire

Image Science & Analysis Laboratory, Johnson Space Center/NASA
This volcano in the Kuril Islands, northeast of Japan, is one of the many active volcanoes in the "Ring of Fire." Shown here in the early stages of a June 12, 2009 eruption, Sarychev Peak is one of many volcanoes along the edge of the Pacific plate.  Mount St. Helens, which had a large eruption on May 18, 1980, and Mount Pinatubo in the Philippines, which exploded in June of 1991 are also in the "Ring of Fire."

Want to join the conversation?

  • spunky sam blue style avatar for user William Lassiter
    in the topic of differentiation the inner core consist of heavier metals iron,& nickel what is the outer core made of?
    (7 votes)
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  • blobby green style avatar for user dottiewallace
    Many think recent earthquakes in North America were caused by "fracking," looking for oil; but do you think they were caused by plate tectonics?
    (6 votes)
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    • blobby green style avatar for user Michael Shane
      No I do not think that plate tectonics plays a role when fracking liquids are pumped into the ground to fracture the underlying rock to get it to release the gas trapped there. There must be tremendous pressures used to fracture the rock and any fracture means that the rock moved ever so slightly,but moved all the same. The movement in my opinion allows the pressures built up over time to finally release themselves in an earthquake.
      (6 votes)
  • blobby green style avatar for user ellinglynch1210
    Tell me more about sea floor spreading and how it pertains to plate tectonics and our earths structure.
    (5 votes)
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  • duskpin seed style avatar for user malienaalittle
    How many feet is it to go to the inner core?
    (4 votes)
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  • starky sapling style avatar for user Gage Matthews
    how do the valcanos form
    (5 votes)
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    • female robot amelia style avatar for user Johanna
      There are three main ways that volcanoes form.

      1. Convergent Boundaries/Subduction
      Convergent boundaries happen where the convection currents in the mantle are going down and pulling two plates together.

      When an oceanic and continental plate meet, the oceanic one is more dense, so it sinks/is forced/subducts under the continental one. As the oceanic plate gets deeper, it gets hotter, and it starts to partially melt. These melted bits (magma) are less dense than their surroundings, so they start to rise. Once the magma rises far enough, it pushes through the plate above it to form volcanoes. An example of this would be the Juan de Fuca plate being subducted beneath the North American plate and forming the Cascades.

      When convection pulls two oceanic plates together, the denser one gets subducted under the less dense one. A similar process of melting, rising, and volcano building then occurs. The Aleutian Islands in Alaska are one volcanic island arc formed this way.

      2. Divergent Boundaries
      Divergent boundaries happen when the mantle's convection is going up and pulls plates apart from each other.

      When two oceanic plates are being pulled apart, magma rises to fill the place in between them, turning into rock when it cools. This creates a mid ocean ridge, like the Mid-Atlantic Ridge.

      Continental plates get thinner where they are being pulled apart, sort of like how a rubber band gets thinner when you stretch it. The thin places in the middle sink to form a rift valley, like Africa's Great Rift Valley. As the magma rises to pull the plates apart, some of it goes through the plate and forms volcanoes like Mount Nyiragongo in the Democratic Republic of the Congo.

      3. Hotspots
      Hotspots happen when mantle plumes (as opposed to just convection currents) rise through the crust above them and make volcanoes. A hotspot is building the Hawaiian islands in the Pacific plate (oceanic). Yellowstone is also made by a hotspot, this time one going up through the (continental) North American plate.
      (3 votes)
  • aqualine ultimate style avatar for user Liam Riley
    How can the pacific plate not be split if it is being pushed in so many ways?
    (5 votes)
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  • leaf red style avatar for user lmcneese
    Comment on one of the slides above- what was interesting? what does it tell us about our future? What does it make you think of?
    (3 votes)
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  • leaf green style avatar for user James Hicks
    In Arkansas and Oklahoma, is the rise in earthquakes contributed to the fracking in Oklahoma and the Madrid Fault line in Arkansas?
    (3 votes)
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  • aqualine ultimate style avatar for user William
    what is the ring of fire?
    (2 votes)
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  • aqualine ultimate style avatar for user louisestephjones
    Under the subtitle 'Andes from Space', what does it mean by the subduction zone?
    (0 votes)
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    • piceratops ultimate style avatar for user trek
      Subduction is the process of one tectonic plate sliding under another tectonic plate.
      subducere is the Latin infinitive verb for to draw from under or to pull up or to raise.
      The English verb subduct means to push under or to move underneath something.
      So, a subduction zone is a region where tectonic plates form a convergent or destructive boundary. Convergent boundaries can form between an oceanic plate and a continental plate or between two oceanic plates or two continental plates. Earthquakes and volcanoes are common in subduction zones because one large piece of crust is sliding under another one.
      (5 votes)