22 August 2008
Hot Lava: Where does it come from?
Posted by Ryan Anderson
You’ve seen it in movies, documentaries, and photographs. Mario and other video game heroes have died countless terrible deaths falling into pits of the stuff, but how much do you really know about lava?
Where does it come from?
Well, volcanoes. And the lava in volcanoes comes from deep in the earth where everything is molten, right? Wrong! It’s true that as you go deeper into the earth, things heat up, but the earth isn’t a crispy rock shell around a gooey molten center. The crust, mantle and inner core of the earth are all solid rock (or iron in the case of the core). The only large portion of the earth’s interior that is liquid is the outer core, and lava does not come from there (again, if it did, it would be molten iron).
People get confused on this point because in school we learn that the mantle flows and convects heat from the core to the surface. Well, that’s true, but it’s misleading. The mantle flows over timescales of millions of years. If you could dig down and pick up a piece of the mantle and whack it with a hammer, it would break. See, hot rocks are a lot like silly putty. Set a ball of silly putty on a table and don’t touch it and it will slowly deform and flow and flatten. Whack that same silly putty with a hammer or pull it really sharply and it will shatter or snap. So that’s how the mantle can flow, given billions of years, but still act like a hard, brittle rock over shorter time periods. The same happens with lava on the surface.
So if the whole mantle is solid, where does hot, molten, fluid lava come from? Well, in certain places, the crystals in the mantle or lower crust can begin to melt. This can happen if there is a hot upwelling from deeper in the earth, as is the case for the Hawaiian islands, or if continental crust is being dragged down into the hot mantle. Temperature, pressure and water are the three main culprits in melting rock, and I’ll explain why.
Temperature is the obvious case: heat something up and eventually it will melt. This is the main source of melting for Hawaii, since it is sitting on a mantle “hot spot” but the other two play a role as well.
When things are under higher pressure, it is much harder for them to break free from their nice, orderly crystals and become free-flowing fluids. That’s why the earth’s inner core is solid even though it is at a temperature much higher than the normal melting point of iron. Likewise, it’s why the mantle is solid, even though it is very hot. But as pressure decreases, for example when the seafloor spreads and releases the pressure on the mantle rocks below it, it becomes much easier for the crystals to melt, and some of them do.
As for water, you would think that water would cool things down and solidify the rock. But it turns out that if you dissolve water in hot rock, it lowers the melting point, much the same way that putting salt on ice lowers the melting point. The result in both cases? The solid melts. Water and other “volatiles” are especially likely to end up dissolved in rocks when an oceanic plate gets subducted, dragging with it water-rich sedimentary rocks. This is why volcanoes are common along subduction zones, such as the entire west coast of the Americas.
So that’s where lava comes from. Stay tuned for a follow-up post, where I’ll talk about the different types of lava flows and show you some pictures I took in Hawaii!
So where exactly does lava come from?
It comes from the partial melting of the rocks in the upper mantle, due to either a “hot spot”, changes in pressure, the presence of water (which lowers the melting point of minerals), or some combination of the three.
this info is ****, it hasn’ helped me at all with my homework! where does the mantle’s heat COME FROM!!!!
Earths core. That where all the heat comes from. Without that we wouldn’t be here nor would the earth and if the core died we all end up like Mars with no life left for existence. I think I should be right…..
Radioactive decay and gravitational contraction. But that’s not what this article was about, it was about where *lava* comes from. Lava is not heat.
Lava IS heat. ‘Heat’ is the vibration of atoms. Lava is molten because the atoms of it vibrate strongly enough for it to be as a liquid.
All matter above absolute zero is heat.
great article; it’s so much fun than my lousy textbook, thank you!
Lava is created by the melting of rock in the lower and upper mantle. The heat used to do this comes from the center of the earth. That heat is made by the constant motion of the inside of the earth or Friction. bah Learn Up kiddos. This is a 13 year old.
@Unknown
Your first sentence is correct, but the heat does not come from friction, it comes mostly from the decay of radioactive elements in the mantle. So, the heat doesn’t come from the center of the earth, it is made throughout the mantle.
SOME heat comes from friction. The center of the Earth is the hottest part and that is the main driving heat force.
Thank you so much. This has really helped me! I’ve used some stuff for my homework, hope that’s OK. I used the silly putty bit;) So the magma has characteristics of both liquid and solid…? And the convection current occurs because of the heat generated from radioactive decay and gravitational contraction…What exactly is gravitational contraction? Thanks so much xo
You’re welcome! Make sure you cite your sources (a.k.a. this site) and that blogs are an acceptable resource for your homework. If not, then you can use the info here to track down more “trustworthy” information elsewhere, such as a geology textbook.
Gravitational contraction is when something gets smaller due to gravity pulling things toward the center of mass. The planets form from gas and dust and as that stuff coalesces, it gives off heat. And even once the planet is formed, heavy things like iron will tend to sink to the core while light things like crustal rock will tend to “float”.
Whenever something falls from high to low, it is giving off potential energy. So when you hold a book up over your head it has lots of potential energy. You let go, and it begins to fall and convert that potential energy into kinetic energy (energy of motion). But then when the book hits the ground what happens to that energy? It doesn’t just disappear, it is transformed again: this time into sound waves and thermal energy.
The same thing happens when gas and dust and rocks come together to form a planet, they transform potential energy, into kinetic energy, into thermal energy. And the same thing happens when iron in the planet sinks to the core: it has to give up some of its potential energy in the form of heat.
thanks u helped me alot.
the core is the hottest part of the sun isnt it i just dont get it,so the volcano eruption is led from the core of the earth
No, the core of the sun is not the hottest part. The hottest part of the sun is the area surrounding it. The surface of the sun is much cooler, and it appears to get cooler the further in you go. Sunspots are the coolest parts on the sun and they are apparently “holes” (or something) into the interior.
The core of the sun IS the hottest part. And it’s at about 27 million degrees Fahrenheit.
And a volcanons eruption is not led from the core of the earth. The core of the earth has nothing to do with a volcano erupting. All of that business happens in the crust.
A volcano erupts from magma coming from the mantle.
i think rocks are coooool
l dont think so
very confusing.How can it be there so much heat so deep inside the earth.How about earthguake!are vulcanoes and earthguake related?
thanks this has helped me alot!
I think lava comes from water,tempreture and pressure. well actually it kind of helped me!
i think lava comes from alot of sources
hi! this was really useful for my project thanks
ummmmmmmmmmmm. i dont understand how people are questioning this brilliant article, it must be true if its so magnificent
my best friend would like to know where and how the lava was formed. her project would like to be more explanitory that mine. If anyone answer this question would be great!
Hey thanks helped me with homework alot way more fun then books nice pictures too!
ohh and some stuff that these people are saying that lava is created inside the crust 😐 to talking about the sun 😐 what eva thanks for the help 🙂
i want to know the main reason why the earth is hot.if any one can help me out i will be happy.am not a science student but am learning to be.any help.
The main reason the inside of the Earth is hot is because of radioactive decay. The second reason is heat that’s been trapped there from when the Earth formed. There is also frictional heat from present movement.
thank for nothing
[…] uniform, so heat is conducted at different rates in different places. There are also unique upwellings of heat in certain areas. The Hawaiian Islands are the result of such an upwelling—heat surging from […]
Mantle rock would not break if you hit with a hammer if it was at mantle temperature. Because to be in a position where you could hit it with a hammer would mean it would have to be under light enough pressure that it would be to fluid.
I meant to have an it between those first hits and withs.
I meant I meant to have an it between the first hit and the first with.
[…] in viscosity within the mantle. Direct measurements of the mantle are only possible through the highly altered lava that emerges from volcanoes, so it has to be imaged indirectly. For this study, the authors decided […]
[…] in viscosity within the mantle. Direct measurements of the mantle are only possible through the highly altered lava that emerges from volcanoes, so it has to be imaged indirectly. For this study, the authors decided […]
I would like to know where lava comes from. Its been spilling out for billions of years. Does that mean that eventually earth will be a solid rock? How would it be replenished? Where does it ccme from? Is the mantle being driven deeper from the lava transferred to the surface? Would this increase the gravity of earth so that now dinosaurs could not walk because of their weight?
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is solid part of lava
Great article. But where does the gooey center of a molten lava cake come from? Please don’t tell me the cake is radio active.
What fills the void that the lava leaves under the earth when it stops erupting?
Great question! We have been asking that often. What fills the void the lava leaves? Why and or when does it Stop? Is there only a certain amount?
that’s why rock music and rock and roll music are both so popular!
What everybody forgets about is gravity…as going toward the center of the earth 0 gravity…..if at the center of the earth which way would you fall….no falling just float .all tbe heavy metals are with in 500 miles of the earth crust….there fore heat is generated some where else….like from heated nickel and a hydrogen environment. Heat is made by an exothermic reaction of nickel converted to copper….5 gm s of nickel can produce 25kw of heat for six mounths ….wow look up rossi reactor Andrea Rossi… this is what keeps the lava flows hot .
The main source of heat is the decay of radioactive elements. Radioactive decay is a natural process; unstable elements like 238U (Uranium) or 40K (Potassium) stabilise with time and produce what we call daughter products: 206P (Lead) for Uranium and 40Ar (Argon) for Potassium. This process produces heat, which represents about 90% of the total heat inside the Earth.
This helped with some of my homework thx! Btw I can’t believe I’m writing this in 2019!
Not good – the mantle is solid rock, I guess, but sure doesn’t look like it in the glowing red diagram…
I have a question that I can’t find the answer to anywhere. What volume or percentage of the earth is magma? Any estimates available?
in the mantle does hot rock rise or fink