plate tectonics Archives

September 16, 2016September 16, 2016 by Matt Williams

What is the Temperature of the Earth’s Crust?

The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com

As you may recall learning in geology class, the Earth is made up of distinct layers. The further one goes towards the center of the planet, the more intense the heat and pressure becomes. Luckily, for those of us living on the crust (the outermost layer, where all life lives) the temperature is relatively steady and pleasant.

In fact, one of the things that makes planet Earth habitable is the fact that the planet is close enough to our Sun to receive enough energy to stay warm. What’s more, its “surface temperatures” are warm enough to sustain liquid water, the key to life as we know it. But the temperature of Earth’s crust also varies considerably depending on where and when you are measuring it.

Earth’s Structure:

As a terrestrial planet, Earth is composed of silicate rocks and metals which are differentiated between a solid metal core, a molten outer core, and a silicate mantle and crust. The inner core has an estimated radius of 1,220 km, while the outer core extends beyond it to a radius of about 3,400 km.

The layers of the Earth, a differentiated planetary body. Credit: Wikipedia Commons/Surachit

Extending outwards from the core are the mantle and the crust. Earth’s mantle extends to a depth of 2,890 km beneath the surface, making it the thickest layer of Earth. This layer is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales.

The upper layer of the mantle is divided into the lithospheric mantle (aka. the lithosphere) and the asthenosphere. The former consists of the crust and the cold, rigid, top part of the upper mantle (which the tectonic plates are composed of) while the asthenosphere is the relatively low-viscosity layer on which the lithosphere rides.

Earth’s Crust:

The crust is the absolute outermost layer of the Earth, which constitutes just 1% of the Earth’s total mass. The thickness of the crust varies depending on where the measurements are taken, ranging from 30 km thick where there are continents to just 5 km thick beneath the oceans.

The crust is composed of a variety of igneous, metamorphic and sedimentary rocks and is arranged in a series of tectonic plates. These plates float above the Earth’s mantle, and it’s believed that convection in the mantle causes the plates to be in constant motion.

Sometimes these plates collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries. In the case of convergent boundaries, subduction zones are often the result, where the heavier plate slips under the lighter plate – forming a deep trench.

A transform boundary is formed when tectonic plates slide horizontally and parts get stuck at points of contact. Stress builds in these areas as the rest of the plates continue to move, which causes the rock to break or slip, suddenly lurching the plates forward and causing earthquakes. These areas of breakage or slippage are called faults.

The Earth's Tectonic Plates. Credit: msnucleus.org — *Illustration of the Earth’s Tectonic Plates and the plate boundaries. Credit: msnucleus.org*

Taken together, these three types of tectonic plate action are what is responsible for shaping the Earth’s crust and leading to periodic renewal of its surface over the course of millions of years.

Temperature Range:

The temperature of the Earth’s crust ranges considerably. At its outer edge, where it meets the atmosphere, the crust’s temperature is the same temperature as that of the air. So, it might be as hot as 35 °C in the desert and below freezing in Antarctica. On average, the surface of the Earth’s crust experiences temperatures of about 14°C.

However, the hottest temperature ever recorded was 70.7°C (159°F), which was taken in the Lut Desert of Iran as part of a global temperature survey conducted by scientists at NASA’s Earth Observatory. Meanwhile, the coldest temperature ever recorded on Earth was measured at the Soviet Vostok Station on the Antarctic Plateau – which reached an historic low of -89.2°C (-129°F) on July 21st, 1983.

That’s quite the range already. But consider the fact that the majority of the Earth’s crust lies beneath the oceans. Far from the Sun, temperatures can reach as low as 0-3° C (32-37.5° F) where the water reaches the crust. Still, a lot balmier than a cold night in Antarctica!

And as geologists have known for some time, if you dig down into the continental crust, temperatures will go up. For example, the deepest mine in the world is currently the TauTona gold mine in South Africa, measuring 3.9 km deep. At the bottom of the mine, temperatures reach a sweltering 55 °C, which requires that air conditioning be provided so that it’s comfortable for the miners to work all day.

So in the end, the temperature of Earth’s crust varies considerably. It’s average surface temperature which depends on whether it is being taken on dry land or beneath the sea. And depending on the location, seasons, and time of day, it can range from sweltering to freezing cold!

And yet, Earth’s crust remains the only place in the Solar System where temperatures are stable enough that life can continue to thrive on it. Add to that our viable atmosphere and protective magnetosphere, and we really should consider ourselves to be the lucky ones!

We’ve written many articles about the Earth for Universe Today. Here’s What are the Layers of the Earth?, Ten Interesting Facts about the Earth, What is the Diameter of the Earth?, What is Earth’s Gravity?, The Rotation of the Earth, and What is Earth’s Crust?

an article about the Earth’s outer core, and here’s an article about the Earth’s crust.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:

July 10, 2015May 26, 2016 by Matt Williams

What is the Pacific “Ring of Fire”?

Sarychev volcano, (located in Russia's Kuril Islands, northeast of Japan) in an early stage of eruption on June 12, 2009. Credit: NASA

What if someone were to tell you that there’s a region in the world where roughly 90% of the world’s earthquakes occur. What if they were to tell you that this region is also home to over 75% of the world’s active and dormant volcanoes, and all but 3 of the world’s 25 largest eruptions in the last 11,700 years took place here.

Chances are, you’d think twice about buying real-estate there. But strangely enough, hundreds of millions of people live in this area, and some of the most densely-packed cities in the world have been built atop its shaky faults. We are talking about the Pacific Ring of Fire, a geologically and volcanically active region that stretches from one side of the Pacific to the other.

Definition:

Also known as the circum-Pacific belt, the “Ring of Fire” is a 40,000 km (25,000 mile) horseshoe-shaped basin that is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. This ring accounts for 452 volcanoes (active and dormant), stretching from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand – with several active and dormant volcanoes in Antarctica closing the ring.

Tectonic Activity:

The Ring of Fire is the direct result of plate tectonics and the movement and collisions of lithospheric plates. These plates, which constitute the outer layer of the planet, are constantly in motion atop the mantle. Sometimes they collide, pull apart, or slide alongside each other; resulting in convergent boundaries, divergent boundaries, and transform boundaries.

*The Pacific Ring of Fire, a string of volcanic regions extending from the South Pacific to South America. Credit: Public Domain*

In the case of the former, subduction zones are often the result, where the heavier plate slips under the lighter plate – forming a deep trench. This subduction changes the dense mantle into buoyant magma, which rises through the crust to the Earth’s surface. Over millions of years, this rising magma creates a series of active volcanoes known as a volcanic arc.

These ocean trenches and volcanic arcs run parallel to one another. For instance, the Aleutian Islands in the U.S. state of Alaska run parallel to the Aleutian Trench. Both geographic features continue to form as the Pacific Plate subducts beneath the North American Plate. Meanwhile, the Andes Mountains of South America run parallel to the Peru-Chile Trench, created as the Nazca Plate subducts beneath the South American Plate.

In the case of divergent boundaries, these are formed when tectonic plates pull apart, forming rift valleys on the seafloor. When this happens, magma wells up in the rift as the old crust pulls itself in opposite directions, where it is cooled by seawater to form new crust. This upward movement and eventual cooling of this magma has created high ridges on the ocean floor over millions of years.

The East Pacific Rise is a site of major seafloor spreading in the Ring of Fire, located on the divergent boundary of the Pacific Plate and the Cocos Plate (west of Central America), the Nazca Plate (west of South America), and the Antarctic Plate. The largest known group of volcanoes on Earth is found underwater along the portion of the East Pacific Rise between the coasts of northern Chile and southern Peru.

Transform Plate Boundary — *The different type of tectonic plate boundaries. Credit: oceanexplorer.noaa.gov*

The San Andreas Fault, stretching along the central west coast of North America, is one of the most active faults on the Ring of Fire. It lies on the transform boundary between the North American Plate, which is moving south, and the Pacific Plate, which is moving north. Measuring about 1,287 kilometers (800 miles) long and 16 kilometers (10 miles) deep, the fault cuts through the western part of the U.S. state of California.

Plate Boundaries:

The eastern section of the Ring of Fire is the result of the Nazca Plate and the Cocos Plate being subducted beneath the westward moving South American Plate. Meanwhile, the Cocos Plate is being subducted beneath the Caribbean Plate, in Central America. A portion of the Pacific Plate along with the small Juan de Fuca Plate are being subducted beneath the North American Plate.

Along the northern portion, the northwestward-moving Pacific plate is being subducted beneath the Aleutian Islands arc. Farther west, the Pacific plate is being subducted along the Kamchatka Peninsula arcs on south past Japan.

The southern portion is more complex, with a number of smaller tectonic plates in collision with the Pacific plate from the Mariana Islands, the Philippines, Bougainville, Tonga, and New Zealand. This portion excludes Australia, since it lies in the center of its tectonic plate.

Indonesia lies between the Ring of Fire along the northeastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor. The famous and very active San Andreas Fault zone of California is a transform fault which offsets a portion of the East Pacific Rise under southwestern United States and Mexico.

Volcanic Activity:

Most of the active volcanoes on The Ring of Fire are found on its western edge, from the Kamchatka Peninsula in Russia, through the islands of Japan and Southeast Asia, to New Zealand. Mount Ruapehu in New Zealand is one of the more active volcanoes in the Ring of Fire, with yearly minor eruptions, and major eruptions occurring about every 50 years.

Krakatau, perhaps better known as Krakatoa, is an island volcano in Indonesia. Krakatoa erupts less often than Mount Ruapehu, but much more spectacularly. Beneath Krakatoa, the denser Australian Plate is being subducted beneath the Eurasian Plate. An infamous eruption in 1883 destroyed the entire island, sending volcanic gas, volcanic ash, and rocks as high as 80 kilometers (50 miles) in the air. A new island volcano, Anak Krakatau, has been forming with minor eruptions ever since.

Mount Fuji, Japan’s tallest and most famous mountain, is an active volcano in the Ring of Fire. Mount Fuji last erupted in 1707, but recent earthquake activity in eastern Japan may have put the volcano in a “critical state.” Mount Fuji sits at a “triple junction,” where three tectonic plates (the Amur Plate, Okhotsk Plate, and Philippine Plate) interact.

The Ring of Fire’s eastern half also has a number of active volcanic areas, including the Aleutian Islands, the Cascade Mountains in the western U.S., the Trans-Mexican Volcanic Belt, and the Andes Mountains. Mount St. Helens, in the U.S. state of Washington, is an active volcano in the Cascade Mountains.

Below Mount St. Helens, both the Juan de Fuca and Pacific plates are being subducted beneath the North American Plate. Its historic 1980 eruption lasted 9 hours and covered 11 U.S. states with tons of volcanic ash. The eruption caused the deaths of 57 people, over a billion dollars in property damage, and reduced hundreds of square miles to wasteland.

Popocatépetl is one of the most active and dangerous volcanoes in the Ring of Fire, with 15 recorded eruptions since 1519. The volcano lies on the Trans-Mexican Volcanic Belt, which is the result of the small Cocos Plate subducting beneath the North American Plate. Located close to the urban areas of Mexico City and Puebla, Popocatépetl poses a risk to the more than 20 million people that live close enough to be threatened by a destructive eruption.

Map of the Earth showing fault lines (blue) and zones of volcanic activity (red). Credit: zmescience.com — *Map of the Earth showing the relation between fault lines (blue) and zones of volcanic activity (red). Credit: zmescience.com*

Earthquakes:

Scientists have known for some time that the majority of the seismic activity occurs along plate boundaries. Hence why roughly 90% of the world’s earthquakes – which is estimated to be around 500,000 a year, one-fifth of which are detectable – occur around the Pacific Rim, where multiple plate boundaries exist.

As a result, earthquakes are a regular occurrence in places like Japan, Indonesia and New Zealand in Asia and the South Pacific; Alaska, British Columbia, California and Mexico in North America; and El Salvador, Guatemala, Peru and Chile in Central and South America. Where fault lines run beneath the ocean, larger earthquakes in these regions also trigger tsunamis.

The most well-known tsumanis to take place in the Ring of Fire include the 2004 Indian Ocean earthquake and tsunami. This was the most devastating tsunami of its kind in modern times, killing around 230,000 people and laying waste to communities throughout Indonesia, Thailand, and Southern Asia.

In 2010, an earthquake triggered a tsunami which caused 4334 confirmed deaths and devastating several coastal towns in south-central Chile, including the port at Talcahuano. The earthquake also generated a blackout that affected 93 percent of the Chilean population.

In 2011, an earthquake off the Pacific coast of Tohoku led to a tsunami that struck Japan and led to 5,891 deaths, 6,152 injuries, and 2,584 people to be declared missing across twenty prefectures. The tsunami also caused meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex.

The Ring of Fire is a crucial region for many reasons. It serves as one of the main boundary regions for the tectonic plates of over half of the globe. It also affects the lives of millions if not billions of people who live in these regions. For many of the people who live in the Pacific Ring of Fire, the reality of a volcanic eruption or earthquake is commonplace and a challenge they have come to deal with over time.

At the same time, the volcanic activity has also provided many valuable resources, such as rich farmland and the possibility of tapping geothermal activity for heating and electricity. As always, nature gives with one hand and takes with the other!

If you have enjoyed this article there are several others on Universe Today that you will find interesting. Here is one called 10 Interesting Facts About Volcanoes. There is also a great article about plate tectonics.

You can also find some good resources online. There is a companion site for the PBS program Savage Earth that talks about the Ring of Fire. You can also check out the USGS site to see a detailed map of the Pacific Ring of Fire and more detailed information about plate tectonics.

You can also listen to Astronomy Cast. Episode 141 talks about volcanoes.

September 9, 2014December 23, 2015 by Elizabeth Howell

Could Plate Tectonics Create Cracks And Odd Terrain In Cold Europa’s Crust?

Reprocessed Galileo image of Europa's frozen surface by Ted Stryk (NASA/JPL/Ted Stryk)

Mysteries abound on icy Europa, that cold moon of Jupiter. Even years after the Galileo spacecraft finished its mission in the Jovian system, scientists are still trying to figure out the nature of the cracks on Europa’s surface. In an exciting find, one new paper suggests that at least part of the terrain could be due to plate tectonics.

If proven, this would be the first time that plate tectonics have been strongly suggested as a process working beyond Earth. On our home planet, scientists believe that this process, which happens as plates of Earth’s crust move, is responsible for creating mountains and volcanoes and earthquakes.

So why do they think this process is happening on Europa? The short answer is, weird terrain. For example, Scientists have seen evidence of what is called extension, which happens when the surface expands and then stuff from the layers below fills in the gap. But there were pieces of that understanding missing until now, the team says.

“We have been puzzled for years as to how all this new terrain could be formed, but we couldn’t figure out how it was accommodated,” stated Louise Prockter, a planetary scientist at Johns Hopkins University Applied Physics Laboratory who co-authored the study. “We finally think we’ve found the answer.”

An illustration of how subducting tectonic plates might work on Jupiter's moon, Europa. This would bring the moon's estimated 10-20 mile (20-30 kilometer) ice shell into the warmer insides of the moon. Credit: Noah Kroese, I.NK — An illustration of how subducting tectonic plates might work on Jupiter’s moon, Europa. This would bring the moon’s estimated 10-20 mile (20-30 kilometer) ice shell into the warmer insides of the moon. Credit: Noah Kroese, I.NK

Despite being pretty confident about the extension, scientists were unable to account for how all the new material arrived.

What the team did was try to model how Europa’s surface looked before how all the cracks appeared, and discovered that 7,700 square miles (20,000 square kilometers) couldn’t be accounted for in the high northern latitudes.

Looking more closely, they found ice volcanoes that they believe was on a surface plate, and missing mountains in what is thought to be a subduction zone. This suggests that stuff from the surface gets pushed underneath — not crushed into each other.

Rendering showing the location and size of water vapor plumes coming from Europa's south pole. Credit: NASA/ESA/L. Roth/SWRI/University of Cologne — Rendering showing the location and size of water vapor plumes coming from Europa’s south pole. Credit: NASA/ESA/L. Roth/SWRI/University of Cologne

“Europa may be more Earth-like than we imagined, if it has a global plate tectonic system,” stated Simon Kattenhorn of the University of Idaho, Moscow, who led the study.

“Not only does this discovery make it one of the most geologically interesting bodies in the solar system, it also implies two-way communication between the exterior and interior — a way to move material from the surface into the ocean — a process which has significant implications for Europa’s potential as a habitable world.”

This adds more fuel to the desire of scientists to head out to Europa. NASA has requests out for ideas for a mission to the icy moon, and in late 2013 scientists reported icy plumes erupting from the moon (spotted in Hubble Space Telescope observations).

A paper on the new research was recently published in Nature Geoscience.

Source: NASA

August 17, 2012December 23, 2015 by Jenny Winder

Scientists Find Clues of Plate Tectonics on Mars

Valles Marineris NASA World Wind map Mars Credit NASA

Caption: Valles Marineris NASA World Wind Map Mars Credit: NASA

Until now, Earth was thought to be the only planet with plate tectonics. But a huge “crack” in Mars’ surface — the massive Valles Marinaris — shows evidence of the movement of huge crustal plates beneath the planet’s surface, meaning Mars may be showing the early stages of plate tectonics. This discovery can perhaps also shed light on how the plate tectonics process began here on Earth.

Valles Marineris is no ordinary crack on the Martian surface. It is the longest and deepest system of canyons in the Solar System. Stretching nearly 2,500 miles, it is nine times longer than Earth’s Grand Canyon.

An Yin, a planetary geologist and UCLA professor of Earth and space sciences, analyzed satellite images from THEMIS (Thermal Emission Imaging System), on board the Mars Odyssey spacecraft, and from the HIRISE (High Resolution Imaging Science Experiment) camera on NASA’s Mars Reconnaissance Orbiter.

“When I studied the satellite images from Mars, many of the features looked very much like fault systems I have seen in the Himalayas and Tibet, and in California as well, including the geomorphology,” he said.

The two plates that Yin calls Valles Marineris North and Valles Marineris South are moving approximately 93 miles horizontally relative to each other. By comparison, California’s San Andreas Fault, which is similarly over the intersection of two plates, has moved about twice as much, because Earth is about twice the size of Mars.

Yin believes Mars has no more than two plates whereas Earth has seven major plates and dozens of smaller ones. As Yin puts it “Earth has a very broken ‘egg shell,’ so its surface has many plates; Mars’ is slightly broken and may be on the way to becoming very broken, except its pace is very slow due to its small size and, thus, less thermal energy to drive it. This may be the reason Mars has fewer plates than on Earth.”

Mars also has several long, straight chains of volcanoes, including three that make up the Tharsis Montes, three large shield volcanoes which includes Olympus Mons, the tallest mountain in the Solar System at 22 km high. These volcanic chains may have formed from the motion of a plate sitting over a “hot spot” in the Martian mantle, in the same way the Hawaiian Islands are thought to have formed here on Earth. Yin also identified a steep cliff similar to cliffs in California’s Death Valley, which are generated by a fault, as well as a very smooth and flat side of a canyon wall which Yin says is also strong evidence of tectonic activity.

Yin also suggests that the fault is shifting occasionally, and may even produce “Marsquakes” every now and again. “I think the fault is probably still active, but not every day. It wakes up every once in a while, over a very long duration — perhaps every million years or more,” he said.

It is not known how far beneath the surface the plates on Mars are located. Yin admits “I don’t quite understand why the plates are moving with such a large magnitude or what the rate of movement is; maybe Mars has a different form of plate tectonics,” Yin said. “The rate is much slower than on Earth.”

“Mars is at a primitive stage of plate tectonics,” Yin added. “It gives us a glimpse of how the early Earth may have looked and may help us understand how plate tectonics began on Earth.”

Yin’s study was published in the August issue of the journal Lithosphere and he also plans to publish a follow-up paper hoping to shed more light on plate tectonics on both Mars and Earth.

Read the abstract.

Find out more at the

September 15, 2010October 16, 2016 by Jerry Coffey

What Is Pangaea?

Continents might be necessary for life, especially complex life. This image shows super-continent Pangaea during the Permian period (300 - 250 million years ago). Credit: NAU Geology/Ron Blakey

So, you are curious about what is Pangaea? It was the supercontinent that existed 250 million years ago during the Paleozoic and Mesozoic eras. During the ensuing millenia, plate tectonics slowly moved each continent to its current position on the planet. Each continent is still slowly moving across the face of our world.

The breaking up and formation of supercontinents appears to have happened several times over Earth’s history with Pangaea being one among many. The next-to-last one, Pannotia, formed about 600 million years ago during the Proterozoic eon. Pannotia included large amounts of land near the poles and only a relatively small strip near the equator connecting the polar masses.

60 million years after its formation Pannotia broke up, giving rise to the continents of Laurentia, Baltica, and Gondwana. Laurentia would eventually become a large portion of North America, the microcontinent of Avalonia(a small portion of Gondwana) would become the northeastern United States, Nova Scotia, and England. All of these came together at the end of the Ordovician.

While this was happening, Gondwana drifted slowly towards the South Pole. These were the early steps in the formation of Pangaea. The next step was the collision of Gondwana with the other land mass. Southern Europe broke free of Gondwana. By late Silurian time, North and South China rifted away from Gondwana and started to head northward across the shrinking Proto-Tethys Ocean.

Movement continued slowly until the land masses drifted until their current positions. The list of oceans and microcontinents is too long to include in this article. We have many articles about this full process here on Universe Today. The evidence for Pangaea lies in the fossil records from the period. It includes the presence of similar and identical species on continents that are now great distances apart.

Additional evidence for Pangaea is found in the geology of adjacent continents, including matching geological trends between the eastern coast of South America and western Africa. The polar ice cap of the Carboniferous Period covered the southern end of Pangaea. Glacial deposits of the same age and structure are found on many separate continents which would have been together in the continent of Pangaea.

We know that the existence of supercontinents has been proven. We know that they have existed at different times in the Earth’s history. Also, we know that the tectonic plates are still moving. Is it possible that there will be another supercontinent someday in the distant future.

We have written many articles about Pangaea for Universe Today. Here’s an article about the Continental Drift Theory, and here’s an article about the continental plates.

If you’d like more info on Pangaea, check out the Pangaea Interactive Map Game. And here’s a link to NASA’s Continents in Collision: Pangaea Ultima.

We’ve also recorded an episode of Astronomy Cast all about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.

Sources:
http://en.wikipedia.org/wiki/Pangaea
http://pubs.usgs.gov/gip/dynamic/historical.html
http://library.thinkquest.org/17701/high/pangaea/

September 10, 2009April 17, 2017 by John Carl Villanueva

What are Plate Boundaries?

In Plate Tectonic Theory, the lithosphere is broken into tectonic plates, which undergo some large scale motions. The boundary regions between plates are aptly called plate boundaries. Based upon their motions with respect to one another, these plate boundaries are of three kinds: divergent, convergent, and transform.

Divergent Boundaries:

Divergent boundaries are those that move away from one another. When they separate, they form what is known as a rift. As the gap between the two plates widen, the underlying layer may be soft enough for molten lava underneath to push its way upward. This upward push results in the formation of volcanic islands. Molten lava that succeeds in breaking free eventually cools and forms part of the ocean floor.

Some formations due to divergent plate boundaries are the Mid-Atlantic Ridge and the Gakkel Ridge. On land, you have Lake Baikal in Siberia and Lake Tanganyika in East Africa.

Convergent Boundaries:

Convergent boundaries are those that move towards one another. When they collide, subduction usually takes place. That is, the denser plate gets subducted or goes underneath the less dense one. Sometimes, the plate boundaries also experience buckling. Convergent boundaries are responsible for producing the deepest and tallest structures on Earth.

Among those that have formed due to convergent plate boundaries are K2 and Mount Everest, the tallest peaks in the world. They formed when the Indian plate got subducted underneath the Eurasian plate. Another extreme formation due to the convergent boundary is the Mariana Trench, the deepest region on Earth.

Transform Boundaries:

Transform boundaries are those that slide alongside one another. Lest you imagine a slippery, sliding motion, take note that the surfaces involved are exposed to huge amounts of stress and strain and are momentarily held in place. As a result, when the two plates finally succeed in moving with respect to one another, huge amounts of energy are released. This causes earthquakes.

The San Andreas fault in North America is perhaps the most popular transform boundary. Transform boundary is also known as transform fault or conservative plate boundary.

Movements of the plates are usually just a few centimeters per year. However, due to the huge masses and forces involved, they typically result in earthquakes and volcanic eruptions. If the interactions between plate boundaries involve only a few centimeters per year, you could just imagine the great expanse of time it had to take before the land formations we see today came into being.

You can read more about plate boundaries here in Universe Today. Here are the links:

Tectonic Plates
Lithosphere

Here are the links of two more articles from USGS:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:
Plate Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html

September 5, 2009December 24, 2015 by John Carl Villanueva

Famous Earthquakes

Earthquakes are among the most devastating forces of nature. What we have are seven of the world’s most famous earthquakes, chronologically listed below. Not all included here are necessarily the strongest (in terms of magnitude) but they made the headlines when they hit. Here they are:

Shaanxi Earthquake of 1556

– This was the deadliest quake ever recorded. It claimed the lives of about 830,000 people. At that time, most inhabitants in the affected areas were living in Yaodongs or artificial caves. They were buried alive when the huge tremors caused the cliffs in which these caves were located in, to collapse.

San Francisco Earthquake of 1906

– Although its tremors were also felt in Southern Oregon, it is the resulting fire in San Francisco that had a more devastating impact on the economy. Is has been often compared recently to Hurricane Katrina because of its similar economic bearing.

The Great Chilean Earthquake of 1960

– Like the one that hit Asia in 2004, this 9.5-rated quake resulted in a massive tsunami reaching up to as high as 10.7 meters. This magnitude is the highest recorded ever. Although the tsunami originated in Cañete, Chile, the waves raced north-westward to Japan and the Philippines, wreaking havoc there.

Great Alaska Earthquake of 1964

– With a magnitude of 9.2, it is the second strongest earthquake to be ever recorded. It caused tsunamis, landslides, and resulted in major landscape changes. Some places near Kodiak is said to have been raised 9.1 meters high, while those near Portage were dropped by 2.4 meters. Here are more articles about Alaska earthquakes.

Great Tangshan Earthquake of 1976

– This is the deadliest quake of the 20th Century, with the number of deaths hitting somewhere near 250,000. Weak building structures and the time this disaster struck (4 am) contributed a lot to that sickening number.

Bam Earthquake of 2003

– The death toll in this tremor reached over 26,000. Like the one in Tangshan, the use of poor construction materials was one of the leading culprits for the deaths. Most of the affected buildings were made of mud bricks.

Indian Ocean Earthquake of 2004

– The resulting tsunami that killed 230,000 people was caused by a subduction between the India and Burma plate. Its 30 m-high waves destroyed virtually everything in its path, making this quake not only one of the most famous earthquakes but also one of the famous natural disasters in history.

Excluding poor building infrastructure, we can see that high death tolls in these famous earthquakes result when the tremors are accompanied by tsunamis. This happens when the quake’s epicenter is found at the bottom of the ocean.

You can read more about famous earthqueakes here in Universe Today. Here are the links:

There’s more about it at USGS. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:
http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake
http://en.wikipedia.org/wiki/2006_Hawaii_earthquake
http://en.wikipedia.org/wiki/1556_Shaanxi_earthquake
http://earthquake.usgs.gov/earthquakes/world/events/1960_05_22.php
http://en.wikipedia.org/wiki/1964_Alaska_earthquake
http://en.wikipedia.org/wiki/1976_Tangshan_earthquake
http://en.wikipedia.org/wiki/2003_Bam_earthquake
http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami

August 31, 2009April 17, 2017 by John Carl Villanueva

What are Divergent Boundaries?

Divergent boundaries are one of the bi-products of plate tectonics. As the name implies, divergent boundaries are formed when two adjacent tectonic plates separate, i.e., when they diverge.

When tectonic plates start to diverge, the linear feature formed is called a rift. Sometimes, the gap widens and sometimes it stops. When the gap eventually widens, it then evolves into a rift valley. Divergent boundaries that occur between oceanic plates produce mid-oceanic ridges.

In places where molten lava is able to move up and fill the gap, volcanic islands are eventually formed. Molten lava that rises eventually cools and forms part of the ocean floor.

One divergent boundary is the Mid-Atlantic Ridge, found at the bottom of the Atlantic and is the longest mountain range in the world. That’s right, the longest mountain range is hidden from our view. Imagine how astonished crew members of the HMS Challenger were when they discovered the massive rise underneath them. The Challenger expedition was dedicated to scientific discoveries the became foundations of oceanography. The Mid-Atlantic Ridge was observed by the HMS Challenger in 1872.

The record for the slowest divergent boundary in the world goes to Gakkel Ridge between the North American Plate and the Eurasian Plate in the Arctic Ocean. Its annual rate of separation is less than one centimeter – that’s about half as fast the rate your fingernails grow. Robotic submersibles belonging to the AGAVE expedition discovered microbial communities of over a dozen new species on this ridge.

Although not as common, rift valleys can also be formed on land. One example is the Basin and Range province in Nevada and Utah. The world’s largest freshwater lakes such as Siberia’s Lake Baikal and East Africa’s Lake Tanganyika are found in rift valleys.

One of the favorite natural laboratories for the study of divergent plate boundaries is Iceland. The Mid-Atlantic Ridge runs beneath Iceland and as the North American Plate moves westward while the Eurasian Plate moves eastward, Iceland will slowly be sliced in half. When water rushes in to fill the widening gap, this huge island of ice will form two smaller islands.

How far can divergent boundaries go? Well if we look at a time frame of 100 to 200 million years, we can easily spot the Atlantic Ocean. What is believed to have been a tiny inlet of water between the formerly merged Europe, Africa, and Americas has now evolved into this vast expanse of water.

You can read more about divergent boundaries here in Universe Today. Here are the links:

There’s more about it at USGS. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:
Plate Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html
http://en.wikipedia.org/wiki/Divergent_boundary
http://geology.com/nsta/divergent-plate-boundaries.shtml

June 30, 2009April 26, 2016 by Stephanie Bender

Continental Crust

The crust is the top layer of the Earth’s Surface. Did you know that there are 2 types, though? One is called the Oceanic Crust, and the other, the Continental Crust. As its name suggests, the Oceanic Crust is the top layer of Earth that forms the ocean floor. The Continental Crust, however, will be our focus.

We walk on top of and dig down through the Continental Crust when we plant or drill. Even if there is an unstable surface at the very top, like sand, the deeper parts of the Crust are made of harder rocks. The large land masses, continents, have bases made from sedimentary, igneous, or metamorphic rocks, as well as any combination thereof. This shield rock is the oldest known; it’s been tested, dated, and found to have been here for 3,960,000,000 years!

Geologists, scientists who study the Earth, believe that shield rock was created when hot molten iron, known as magma cooled. If their math’s correct, it happened around the time these rocks formed, almost 4 billion years ago, right? Some of those rocks were so big it took a long time for them to cool. So, even if the rocks were formed 3.9 billion years ago, they might not have cooled for quite some time. Many estimate that the Continental Crust wasn’t completely hard for another 60,000,000 to 160,000,000 years.

The top portion of this rock has another name, platform rock. The oldest-known platform rocks are approximately 600,000,000 years old, and can be found in central North America. The sedimentary rock ranges from 1,000 to 2,000 meters thick; that is equivalent to more than a half mile to 1.25 miles. When we put the top and bottom portions of the Continental Crust together, we get what scientists call, a craton. Most cratons are stable and haven’t been damaged by earthquakes or volcanoes for hundreds of millions of years.

Around the edges are the continental margins, mostly created by sedimentary rock originally found in the oceans. How is that possible, you ask? Well, it’s due to earthquake and volcanic activity. In this case, it’s mainly due to a phenomenon called, subduction. You see, the Earth fits together like a puzzle; and, if you try to place the wrong piece into a spot where it fits, but isn’t quite right, what happens? Another piece might pop out of place. Sometimes, a continental margin works its way under the oceanic crust. When that occurs, the oceanic layer ends up on top of the continental margin. This is subduction. The most well-known place for this is along The Ring of Fire, an area that covers the edges along the Pacific Ocean. This is why so many and such violent earthquakes, volcanic eruptions, and tsunamis occur in that part of the world.

Universe Today has a wealth of information on this and other related topics. Here are just 2 of those available. The first is entitled,
Earth, Barely Habitable?.

The second is called, Interesting Facts About Planet Earth.

Universe Today also hosts Astronomy Cast, a science program that covers a variety of subjects. Episode 51: Earth, explains this subject in greater detail.

The Encyclopedia of Earth , by Michael Pidwirny has some excellent information, too.

Sources:
USGS
Science Daily