Asked by juhh
Extrusive igneous rocks often have air pockets, but intrusive igneous rocks never do. Why do you think this is the case.
All Answers 1
Answered by
GPT-5 mini
AI
Because of differences in pressure and cooling rate.
- Magma contains dissolved volatiles (H2O, CO2, SO2, etc.). At the high pressures found deep underground those gases stay dissolved in the melt.
- When magma rises toward the surface the pressure drops and the volatiles exsolve into bubbles. If the melt reaches the surface (an extrusive eruption) it cools very quickly and the bubbles are trapped in the solidifying lava, producing vesicles (air pockets) — e.g., pumice, scoria, vesicular basalt.
- Intrusive magma cools slowly while still buried under high confining pressure. The slow cooling and high pressure keep gases dissolved or allow them to escape over time through the still-fluid melt or surrounding rock, so bubbles do not get trapped. The result is a coarse-grained, dense, crystalline rock (e.g., granite, gabbro) with essentially no vesicles.
(Shallow intrusions or unusual conditions can produce rare cavities, but in general the pressure/cooling differences explain why extrusive rocks commonly have air pockets and intrusive ones do not.)
- Magma contains dissolved volatiles (H2O, CO2, SO2, etc.). At the high pressures found deep underground those gases stay dissolved in the melt.
- When magma rises toward the surface the pressure drops and the volatiles exsolve into bubbles. If the melt reaches the surface (an extrusive eruption) it cools very quickly and the bubbles are trapped in the solidifying lava, producing vesicles (air pockets) — e.g., pumice, scoria, vesicular basalt.
- Intrusive magma cools slowly while still buried under high confining pressure. The slow cooling and high pressure keep gases dissolved or allow them to escape over time through the still-fluid melt or surrounding rock, so bubbles do not get trapped. The result is a coarse-grained, dense, crystalline rock (e.g., granite, gabbro) with essentially no vesicles.
(Shallow intrusions or unusual conditions can produce rare cavities, but in general the pressure/cooling differences explain why extrusive rocks commonly have air pockets and intrusive ones do not.)
Submit Your Answer
We prioritize human answers over AI answers.
If you are human, and you can answer this question, please submit your answer.