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Earthquakes, Volcanoes and The Ring of Fire - I

Thursday, March 17, 2011

Indonesia, Japan, Philippines, New Zealand, Chile – familiar sounding names for volcanic eruptions and earthquakes isn’t it? And vaguely I knew that it’s cos they fall in the oft-heard of Ring of Fire. But now after the recent disturbances in Japan, I really wanted to find out about this ring and share the same in the simplest way possible. I want to permanently remember this information, and hopefully those of you who are interested will manage to do the same.

The ABCs

Think of the earth’s surface as a jigzaw puzzle. Tectonic plates are pieces of that jigzaw puzzles. What lies above these pieces is a thin layer of crust topped with the seas (oceanic crust) and a thick layer of crust topped with the ground we stand on (continental crust). Collectively it’s called the lithosphere. So these jigzaw pieces are kinda all little different in what they are made of. What lies below is a molten matter known as asthenosphere. Now imagine that these jigzaw pieces are kids forced to share a bed. They are constantly jostling and sliding to find a comfort zone. If that bed they are sharing is a water bed – then the whole thing will get horribly wobbly. And that exactly what happens. This jostling and sliding of the tectonic plates is responsible for the earthquakes, volcanoes eruptions, and also mountain formations. Side effects include tsunamis.

The point where these plates join (boundaries) is what matters to us the most, as it is at these points of friction that the activities occur. They are manifested as fault lines on the earth's crust. The friction could be a result of either the plates moving away from each other or sliding/colliding with each other. At most times they are simply grinding against each other rather gently, but still over a period of time result in pent up energy releasing through earthquakes. Volcanoes will occur when the molten lava and gasses are disturbed and find a way to escape through these joining points. Both volcanoes and earthquakes can result from a collision or a moving away of the plates. Think back to the jigzaw puzzle analogy. Push them against each other and they get all crushed. Pull them apart and then your puzzle falls apart. Unfortunately since our jigzaw (the plates in this case) rest on a liquid base, the movement is unavoidable.

Fault lines are not invisible. Check out their awesomeness through these images.

  • Fault line in New Zealand

Tectonic plate movements

Skip to Pacific Ring of Fire

With the interaction of the tectonic plates – three things happen:
  1. They move apart
  2. They grind against each other
  3. They slide/collide – one ends on top of the other
When they move apart When they grind against each other When they slide/collide
Referred to as divergent boundaries/faults.
  • When the plates move apart they cause rifts that are filled up by magma from below leading to new crust formation
  • These typically occur in the oceanic crust and result in mid oceanic ridges that are underwater mountains that sometimes break the surface like Iceland and also result in formation of volcanoes and oceanic trenches.
  • When they occur in continental crust (land) they form rifts on land like the Great Rift Valley.
The fault lines along the divergence can result in earthquakes
Referred to as transform or conservative boundaries/faults
  • When the plates grind against each other the crust is neither created nor destroyed.
  • Most of these are found on the ocean floor.
  • Although the plates grind in harmony the built up stress over time can result in the release of energy through earthquakes.
  • Volcanoes are not a characteristic of conservative faults

Referred to as convergent boundaries/faults.
  • oceanic-continental slide:When a plate comprising of oceanic crust collides with a continental crust plate the slides under the continental crust and sometimes forms a volcanic arc like that of the Andes in South America.
  • oceanic-oceanic slide: When both the plates comprise of oceanic crust collide they form island arcs like the Indonesian archipelago.
  • continental-continental collision: When two continental plates collide they result in inland mountain ranges like the Himalayas.

    An oceanic-continental or oceanic-oceanic slide results in a process known as subduction. The subduction process is what causes the majority of the world’s earthquakes.

The Pacific Ring of Fire 

The Pacific tectonic plate is one of the largest plates and is in constant friction with close to seven other surrounding plates. The boundaries it shares with the plates are of all three types. It’s moving away from some, getting too close to some, and sliding past some. The ring forms a horseshoe shape starting from New Zealand running along the east side of Asia touching Alaska and coming down the west coast of North America to South America, and eventually merging with Antartica. The ring is actually a continuous belt of volcanic arcs and oceanic trenches (talked about in the previous section). So if you are living in a country that is either atop one of these or near one of these then it’s almost like sitting on huge landmine that can blow off any second.

And the blow offs occur quite regularly. As the most active region for earthquakes and volcanoes of the world, the ring experiences a minor occurrence of volcanic eruptions or earthquakes everyday, and a moderate one on a weekly basis. People living in places like Japan, Indonesia, Alaska, California are probably familiar with these effects. Indonesia particularly is resting on a highly volatile zone. Not only does it find itself in the Ring of Fire on the north-east side, but is also close to the Alpide belt on the south and west side. The Alpide belt is the second most active and dangerous belt. Together these two belts generate around 96% of all earthquakes on earth. It’s almost like the two belts are playing Foosball with Indonesia.

Naturally this region offers great bio-diversity and ecological makeup. This I will explore in part II.

Some very interesting earthquake facts are presented here.