Question: How and why do structure of volcanos vary?

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  1. Great question! The structure of volcanoes vary with the type of magma, amount of gases, and the presence of water. Volcanoes that form from lava with low silica will be broad as the lava can flow easily and for long distances. The more silica content in the lava, and the more viscous it is, the steeper the sides of the volcano. Magma with a high gas concentration will be more explosive and will produce ash and bombs that will deposit on the flanks of the volcanoes contributing to the steepness of the slope. Explosive volcanoes that erupt violently will leave a crater on its summit (called a caldera when it is huge).

    If the volcano is erupting under water (mid-oceanic rift) it will produce lava flows called pillow lavas because of the shape the lava forms as it cools rapidly under water. Volcanoes capped by ice (Iceland) may have flat summits as the result of the interaction with ice.


  2. Hi 6fkabrea,

    Daniel provided you with a great answer to your question. What I could add is a short documentary, that I found to be useful:

    Hope it helps! 🙂


  3. Hi 6fkabrea,

    Fantastic question – I think Daniel has summed it up very well!
    I know this doesn’t really relate to your question but you can also get monogenetic volcanoes, which can form on the flanks of bigger volcanoes or in calderas or along tectonic plate boundaries. They only erupt once and have a very small surface area (normally 1km^3). One type of monogenetic volcano is called a cinder cone – these can be found in Iceland.


  4. Hi 6fkabrea, I think Daniel has a really good answer there and I really like the documentary that you have put up here Denise!


  5. This will be on the list of things I learned today 😉