What exactly causes huge plates to move and collide with such a colossal force? How do they not create extremely wide trenches in places where they move apart? Why isn’t the place where they move apart just molten magma? What is the force propelling magma and ash upwards during an eruption? I searched on the Internet, but I want a deeper explanation, which I couldn’t find. TIA!
In: 1
Magma moves mostly due to convection. When an upward moving magma stream reaches the Earth’s mantle/crust it spreads out, draging techtonic plates with it. Where plates separate, volcanic eruptions occur. Magma from these eruptions eventually cools and seals the gap for a while.
These processes happen so slowly as to make the fast majority of volcanos seem dormant.
Magma moves mostly due to convection. When an upward moving magma stream reaches the Earth’s mantle/crust it spreads out, draging techtonic plates with it. Where plates separate, volcanic eruptions occur. Magma from these eruptions eventually cools and seals the gap for a while.
These processes happen so slowly as to make the fast majority of volcanos seem dormant.
Magma moves mostly due to convection. When an upward moving magma stream reaches the Earth’s mantle/crust it spreads out, draging techtonic plates with it. Where plates separate, volcanic eruptions occur. Magma from these eruptions eventually cools and seals the gap for a while.
These processes happen so slowly as to make the fast majority of volcanos seem dormant.
The earth was formed when a bunch of rocks collided with each other. Those collisions caused a lot of heat just from the large forces involved. The only way for heat to escape is through radiation into space, which is pretty inefficient. So much of the heat from way back then is still trapped beneath the crust and is the engine that drive these processes.
The heat is greatest at the core. So magma near the core is hotter than magma near the crust. Hotter things are less dense, so that hotter magma starts rising and the colder magma starts sinking. As the hotter magma rises, it starts cooling down because it’s further away from the hot core. And vice versa for the cool magma sinking down. This cycle of rising and sinking causes massive currents. The Earth’s crust is just a bunch of little rafts riding these currents.
> How do they not create extremely wide trenches in places where they move apart?
They do. There’s the [East African Rift](https://en.wikipedia.org/wiki/East_African_Rift) on land and the [Mid-Atlantic Ridge underwater](https://en.wikipedia.org/wiki/Mid-Atlantic_Ridge). Tectonic plates just move really slow, millimeters per year. And lava solidifies basically instantly. So new rock basically fills the gap very quickly. In the Atlantic, it’s filling the gap so quickly it’s formed a mountain range instead of a trench.
The earth was formed when a bunch of rocks collided with each other. Those collisions caused a lot of heat just from the large forces involved. The only way for heat to escape is through radiation into space, which is pretty inefficient. So much of the heat from way back then is still trapped beneath the crust and is the engine that drive these processes.
The heat is greatest at the core. So magma near the core is hotter than magma near the crust. Hotter things are less dense, so that hotter magma starts rising and the colder magma starts sinking. As the hotter magma rises, it starts cooling down because it’s further away from the hot core. And vice versa for the cool magma sinking down. This cycle of rising and sinking causes massive currents. The Earth’s crust is just a bunch of little rafts riding these currents.
> How do they not create extremely wide trenches in places where they move apart?
They do. There’s the [East African Rift](https://en.wikipedia.org/wiki/East_African_Rift) on land and the [Mid-Atlantic Ridge underwater](https://en.wikipedia.org/wiki/Mid-Atlantic_Ridge). Tectonic plates just move really slow, millimeters per year. And lava solidifies basically instantly. So new rock basically fills the gap very quickly. In the Atlantic, it’s filling the gap so quickly it’s formed a mountain range instead of a trench.
The earth was formed when a bunch of rocks collided with each other. Those collisions caused a lot of heat just from the large forces involved. The only way for heat to escape is through radiation into space, which is pretty inefficient. So much of the heat from way back then is still trapped beneath the crust and is the engine that drive these processes.
The heat is greatest at the core. So magma near the core is hotter than magma near the crust. Hotter things are less dense, so that hotter magma starts rising and the colder magma starts sinking. As the hotter magma rises, it starts cooling down because it’s further away from the hot core. And vice versa for the cool magma sinking down. This cycle of rising and sinking causes massive currents. The Earth’s crust is just a bunch of little rafts riding these currents.
> How do they not create extremely wide trenches in places where they move apart?
They do. There’s the [East African Rift](https://en.wikipedia.org/wiki/East_African_Rift) on land and the [Mid-Atlantic Ridge underwater](https://en.wikipedia.org/wiki/Mid-Atlantic_Ridge). Tectonic plates just move really slow, millimeters per year. And lava solidifies basically instantly. So new rock basically fills the gap very quickly. In the Atlantic, it’s filling the gap so quickly it’s formed a mountain range instead of a trench.
Because the tectonic plates are a thin layer (relative to the size of the planet overall) of mostly solid rock floating on a massive layer of viscous magma (the mantle).
Think of it like thin ice on a puddle. If you step on the puddle, water wells up through the cracks in the ice.
Now imagine that water is both thick, like jam, and boiling hot. Because it’s being heated, it rolls and boils (like water boiling on a stove). Those rolling currents are “convection.”
Those convection currents are what is pushing the plates around on the surface.
Where the plates slide apart, magma wells up to fill the hole (this is what happens at the Mid-Atlantic Ridge, where two plates are moving apart).
Bonus: In some places, there’s an upwelling of extra hot magma and it partially melts the crust above it (kind of like a hot spring under a lake would melt the ice in one spot in the wintertime). Those are “hot spots” and they account for areas of volcanic activity that are far from plate boundaries, like Yellowstone, or Hawaii.
Because the tectonic plates are a thin layer (relative to the size of the planet overall) of mostly solid rock floating on a massive layer of viscous magma (the mantle).
Think of it like thin ice on a puddle. If you step on the puddle, water wells up through the cracks in the ice.
Now imagine that water is both thick, like jam, and boiling hot. Because it’s being heated, it rolls and boils (like water boiling on a stove). Those rolling currents are “convection.”
Those convection currents are what is pushing the plates around on the surface.
Where the plates slide apart, magma wells up to fill the hole (this is what happens at the Mid-Atlantic Ridge, where two plates are moving apart).
Bonus: In some places, there’s an upwelling of extra hot magma and it partially melts the crust above it (kind of like a hot spring under a lake would melt the ice in one spot in the wintertime). Those are “hot spots” and they account for areas of volcanic activity that are far from plate boundaries, like Yellowstone, or Hawaii.
Because the tectonic plates are a thin layer (relative to the size of the planet overall) of mostly solid rock floating on a massive layer of viscous magma (the mantle).
Think of it like thin ice on a puddle. If you step on the puddle, water wells up through the cracks in the ice.
Now imagine that water is both thick, like jam, and boiling hot. Because it’s being heated, it rolls and boils (like water boiling on a stove). Those rolling currents are “convection.”
Those convection currents are what is pushing the plates around on the surface.
Where the plates slide apart, magma wells up to fill the hole (this is what happens at the Mid-Atlantic Ridge, where two plates are moving apart).
Bonus: In some places, there’s an upwelling of extra hot magma and it partially melts the crust above it (kind of like a hot spring under a lake would melt the ice in one spot in the wintertime). Those are “hot spots” and they account for areas of volcanic activity that are far from plate boundaries, like Yellowstone, or Hawaii.
So, other answers have done a decent job of covering how plates move. The one small correction here is that the mantle is actually solid, but just a bit “soft”. Melting does occur beneath areas of volcanic activity.
But let’s turn to volcanoes. Magma underground usually has some gas in it, which stays dissolved because the magma is under pressure. This pressure mostly comes from the weight of the rock lying on top of it. As magma rises, the pressure on it is reduced. The gas can no longer stay dissolved and forms bubbles. As pressure decreases even more, the bubbles expand and force lava and/or ash out of the volcano’s vent. The process is actually rather like opening a can of soda after shaking it.
Latest Answers