Animals Wild Cities Morocco has 3 million stray dogs. Meet the people trying to help. Animals Whales eat three times more than previously thought. Environment Planet Possible India bets its energy future on solar—in ways both small and big. Environment As the EU targets emissions cuts, this country has a coal problem. Paid Content How Hong Kong protects its sea sanctuaries. History Magazine These 3,year-old giants watched over the cemeteries of Sardinia. Magazine How one image captures 21 hours of a volcanic eruption.
Science Why it's so hard to treat pain in infants. Science The controversial sale of 'Big John,' the world's largest Triceratops. Science Coronavirus Coverage How antivirals may change the course of the pandemic. Science Coronavirus Coverage U. Travel A road trip in Burgundy reveals far more than fine wine. Travel My Hometown In L. Travel The last artists crafting a Thai royal treasure. Subscriber Exclusive Content. Why are people so dang obsessed with Mars? The mechanism by which tectonic plates move is still a subject of much debate among Earth scientists.
The Earth is dynamic thanks to its internal heat, which comes from deep within the mantle from the breakdown of radioactive isotopes. However, this theory is now largely out of favour, with modern imaging techniques unable to identify mantle convection cells that are sufficiently large to drive plate movement.
Indeed, it is now accepted that plates and the mantle are a coupled system with plates moving by a process known as ' slab pull ' which helps to drive mantle convection patterns rather than the other way around. This can cause volcanoes.
At divergent boundaries, plates move apart from each other. When this happens, new plate material forms. Two plates pushed together create a convergent fault. If one plate is oceanic and the other continental, the edge of the oceanic plate will be pushed down. Oceanic plate. When the less dense, lighter continental plate overrides the oceanic plate a subduction zone forms.
Because the oceanic plate is bent and driven down, a deep trench forms at this collison point. These trenches are the lowest points on the Earth's crust. One trench is a mile deeper than Mount Everest is tall! As the oceanic plate descends into the mantle some of it melts. This material moves into the mantle above the plate and causes the mantle to melt. This liquid rock, called magma, rises to the surface because it is less dense then the surrounding rock.
If the magma reaches the surface of the Earth, a volcano forms. As the mantle rocks melt they form magma. The magma collects in a magma pool. Because the magma is less dense than the surrounding mantle material it will rise. Pressure in the magma cracks the overlying rocks. Then the magma injects into the crack. This process repeats thousands of times, bring the magma towards the surface.
A volcano will form if the magma reaches the surface. When magma does reach the surface it is then called lava. You will learn more about volcanoes in the following lessons.
0コメント