Plate Tectonics, Hold on! The Surface of the Earth Moves

So why do mountain ranges form, earthquakes happen, volcanoes erupt and Islands appear? Have they been here since the beginning of time perhaps created by a roving asteroid or comet Or perhaps there was a massive collision of  two planets when the Earth got formed creating islands and mountains. This is all complete rubbish of course most of the things occur due to plate tectonics.

So what is plate tectonics? The plate part of plate tectonics gives it away a little. Plate tectonics relates to the movement of areas of the surface of Earth over time. Plate tectonics doesn’t have to mean that the surface of the earth alone moves, it can also relate to other planets as well.

The Earth make up

To explain plate tectonics scientists divide the outer layers of the Earth into the lithosphere and the asthenosphere. Wow! Those are two large and pretty ungainly words. If you break lithosphere down into two words litho is Greek for stone and we all know what a sphere is (hopefully). So that means that lithosphere really means stone sphere.

Astheno in asthenosphere means weak giving us weak sphere. There are other names for the layers of the Earth (relating to the chemical composition and division) but these are not to be confused with the lithosphere and asthenosphere. The lithosphere and asthenosphere refer to the heat transfer and also the behaviour of these layers. This is all they refer to and are nothing to do with the mantle or the crust (think of them as being snobby cousins).

The lithosphere loses heat by conduction, conduction being very simple and happening around us all the time. If you touch a kettle for instance the heat will be transferred from the kettle to your finger and you will go Oww and probably utter a few words. The transfer of heat from the kettle to your finger is happening by conduction.

Convection

The asthenosphere on the other hand is different. It transfers heat by what is called convection. This happens when the rock is not totally solid and our plastic layer of malleable asthenosphere allows heat to travel upwards in rocks then on the sides of this upward column there is a downward movement of cold rock.

For this you can see, perhaps, that plate tectonics is actually the lithosphere (which is solid rock) riding over a liquid rock asthenosphere. This movement is only about 2 to 16 cm per year so don’t get too alarmed. You won’t fall over and lose your balance unless of course you’re experiencing an earthquake.

With the lithosphere riding on top of the asthenosphere we could  just have one big plate all over the Earth and we would never know the difference. The Earth is not like that though and the surface of the Earth is broken up into various regions called plates which move around separately from each other.

This as you can imagine causes collisions and also gaps between the plates. When the two plates meet one of the plates it is forced underneath the other plate going back down inside the Earth to be recycled. The other plate is pushed up and forms mountain ranges such as the Himalayas. Earthquakes, volcanoes, mid ocean ridges (which produce islands) and oceanic trenches are also formed in this area. Most of the world’s active volcanoes occur along plate boundaries with the Pacific plate ring of fire being the most active and widely known.

Map of world and tectonic plates

So why don’t the plates just stay still, why do they move? That’s quite a complicated question and not fully understood at the moment but a decent theory is that the heat from the asthenosphere is believed to be the driving force for the plates. Also, the dense lithosphere sinks into the less dense asthenosphere at the place where the two plates meet causing a driving force for the plates.

So from this you can see there is a constant refreshing of the Earth’s surface as volcanoes and mountain ranges are formed and the old worn out crust is sucked into the Earth and melted down for future use.

Just so we don’t get anti plate tectonically it might be a good idea to list the good and bad things associated with plate tectonics.

• Earthquakes are a major problem to us sometimes. Some of Earth’s major cities are situated on the top of fault lines (where the two plates meet). The long-term benefits outweigh the short term tragedies in these cities. The money counters when they build their big buildings and make lots of cash way up the cost of earthquake damage and income between earthquakes. Earthquakes don’t happen every day, they are years apart and this means that it is economically viable to build towns on fault lines. There is no price on human life though.
• Volcanoes have caused many a disaster but are much more predictable than earthquakes and the effects can often be avoided unless you get a pigheaded farmer not willing to move out of his house.
• Earthquakes can occur at the boundary of two plates are very dangerous as they can produce tsunamis. This occurs because the ocean floor moves by a couple of metres and can upset the water giving it motion. Tsunamis rarely bother ships in the ocean but closer to the land they can be devastating.

The thing about earthquakes and volcanoes is that you don’t have to live in that region.

Pyroclastic flows at Mayon Volcano

The good things about plate tectonics:

• the production of mountains which is very nice for mountain climbers. Mountain ranges also help in the production of oil and natural gas and these resources are found in the geologic basins that flank mountain ranges formed by plate tectonics.
• Volcanoes cause resurfacing of the land and over time improved fertility. They can be the most fertile soils on earth such as the Windward side of the island of Hawaii where growth can take only a few hundred years after an eruption. This is obviously very tempting and people use in this ground for the growth of crops.
• Ore deposits are produced by volcanoes but aren’t necessarily spewed out in an eruption. Sometimes ore deposit cool slowly beneath the surface of the volcano to form a wide variety of crystalline rocks.
• Volcanoes can also produce geothermal energy which is really just the use of heat produced by the volcano. This heat produces steam and can be used to drive turbines and generate electrical power.

So, one thing leads to another. The heat inside the Earth which was produced when the Earth formed by all the collisions turning kinetic energy into potential energy, radioactive heat from uranium and thorium and potassium and heat due to compression within the Earth’s layers has really done us a favour.

The heat produces movement of the surface of the earth which in turn causes volcanoes, earthquakes and where plates meet mountains or islands. In the short term destruction is caused but compared to the long-term benefits this is minimal.

So, if you feel that there is a city at the centre of the Earth with an alien civilisation that just hasn’t introduced itself yet then think again.

A podcast on plate tectonics-

Join the forum discussion on this post - (1) Posts