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22-10-2021, 11:24 AM
Why doesn't the lava melt the volcano itself?
The nesting wall is made of an older volcanic material with a higher melting point. In addition, pressure and thermal conductivity influence
We are seeing these days, in the eruption of the new volcano on La Palma , how the lava destroys what it finds in its path and, however, as the question says, it does not melt the volcano itself. In principle, all the elements that have a melting point lower than the temperature of the lava itself , which has values between 800 ° C and 1200 ° C, are swallowed up by the washings and integrated into their mass: homes, roads, furniture urban, industrial and agricultural facilities, etc.
However, we see that what in geology we call "nesting rock" resists. This embedding rock is the material that magma passes through on its ascent to the surface and its exit to the outside. The reasons why it is not founded are several. The main one is that the material that rises from the earth's mantle and ends up leaving through the mouths of the volcano is a fluid rock of a baseitic nature that is at a lower temperature than that required to melt the rock it passes through. This rock that forms the nesting wall has a different composition than the one that rises because it is an older volcanic material with a higher melting point.
In addition, pressure influences. The rock that forms the volcanic structure is subjected to greater pressure than the elements on the surface. The latter only suffer atmospheric pressure, but the rocks inside are also under what we call lithostatic pressure, which is the pressure exerted by the overlapping layers of material. The higher the pressure, the higher the melting point. So this characteristic adds to the difficulty for the lava to destroy the rock that forms the cone of the volcano.
The rock of the volcanic building is a kind of fusion armored chest, mainly due to its nature
And there is yet another reason to add: rocks have low thermal conductivity, and more so if they contain water. I give you an example to give you an idea: under the same conditions, while copper has a thermal conductivity of 385 W / Km, olivine (a mineral very present in volcanic rocks) has a thermal conductivity of 5 W / Km This means that the temperature and heat of the magma, as it ascends through the volcanic structure, hardly spreads and interferes little with the rock it passes through.
But just because it doesn't melt it doesn't mean it doesn't alter it in some way. This ascending magma does leave a certain trace on the walls that is called anathexis or anathexis, which is a partial fusion of the rocks; an aureole of contact that is fading. And it is partial because, as you know, the rocks are composed of different minerals and not all those that make up the nesting wall have the same melting point, so some are more affected than others by the temperature of the rising lava.
In conclusion, the answer to your question is that the rock of the volcanic building is a kind of chest armored to fusion, mainly due to its nature, since the melting point of these rocks is higher than the temperature of the rising magma; to the higher pressure to which they are subjected, which, in turn, also increases their melting point, and to the low thermal conductivity of rocky materials that barely propagate heat.
Rosa María Mateos is a doctor in Geology and researcher at the Geological and Mining Institute of Spain IGME-CSIC
The nesting wall is made of an older volcanic material with a higher melting point. In addition, pressure and thermal conductivity influence
We are seeing these days, in the eruption of the new volcano on La Palma , how the lava destroys what it finds in its path and, however, as the question says, it does not melt the volcano itself. In principle, all the elements that have a melting point lower than the temperature of the lava itself , which has values between 800 ° C and 1200 ° C, are swallowed up by the washings and integrated into their mass: homes, roads, furniture urban, industrial and agricultural facilities, etc.
However, we see that what in geology we call "nesting rock" resists. This embedding rock is the material that magma passes through on its ascent to the surface and its exit to the outside. The reasons why it is not founded are several. The main one is that the material that rises from the earth's mantle and ends up leaving through the mouths of the volcano is a fluid rock of a baseitic nature that is at a lower temperature than that required to melt the rock it passes through. This rock that forms the nesting wall has a different composition than the one that rises because it is an older volcanic material with a higher melting point.
In addition, pressure influences. The rock that forms the volcanic structure is subjected to greater pressure than the elements on the surface. The latter only suffer atmospheric pressure, but the rocks inside are also under what we call lithostatic pressure, which is the pressure exerted by the overlapping layers of material. The higher the pressure, the higher the melting point. So this characteristic adds to the difficulty for the lava to destroy the rock that forms the cone of the volcano.
The rock of the volcanic building is a kind of fusion armored chest, mainly due to its nature
And there is yet another reason to add: rocks have low thermal conductivity, and more so if they contain water. I give you an example to give you an idea: under the same conditions, while copper has a thermal conductivity of 385 W / Km, olivine (a mineral very present in volcanic rocks) has a thermal conductivity of 5 W / Km This means that the temperature and heat of the magma, as it ascends through the volcanic structure, hardly spreads and interferes little with the rock it passes through.
But just because it doesn't melt it doesn't mean it doesn't alter it in some way. This ascending magma does leave a certain trace on the walls that is called anathexis or anathexis, which is a partial fusion of the rocks; an aureole of contact that is fading. And it is partial because, as you know, the rocks are composed of different minerals and not all those that make up the nesting wall have the same melting point, so some are more affected than others by the temperature of the rising lava.
In conclusion, the answer to your question is that the rock of the volcanic building is a kind of chest armored to fusion, mainly due to its nature, since the melting point of these rocks is higher than the temperature of the rising magma; to the higher pressure to which they are subjected, which, in turn, also increases their melting point, and to the low thermal conductivity of rocky materials that barely propagate heat.
Rosa María Mateos is a doctor in Geology and researcher at the Geological and Mining Institute of Spain IGME-CSIC
