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I've found most websites saying that 100 kilometers is the maximum size of a caldera volcano, but none of them explain why this is the case. So, can caldera volcanoes get any bigger than this and why is that the case?

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    $\begingroup$ The biggest caldera (Toba) on Earth is about 100x30 km. But it certainly doesn't proove it can't be bigger. It's not as if there were many other that were 99km big $\endgroup$
    – Madlozoz
    Oct 30 '20 at 14:29
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I am not a geologist to give you a detailed explanation, but I guess the reason is in the resistance of the crust.

A caldera forms when a hot spot from the mantle forms a "bubble" of magma beneath the crust. If the caldera is too large, the thin crust will simply break down under its own weight into smaller pieces, letting the magma out and not allowing pressure build up.

Sort of what happens if you make a too large pizza base by spreading the dough, it will rip open in some places.

I guess that for Earth about 100 km is the largest size you can get before getting too spread. Different planets with different composition and gravity might have different limits.

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  • $\begingroup$ "Lava pool" (more like hot-rock pool) can be much larger than that (up to thousands kilometers), but that would not be a caldera volcano - this is a differernt proccess. The max size of a caldera defined by maximum size of a plum - it's about 100 km (on Earth). $\endgroup$
    – ksbes
    Oct 29 '20 at 9:33

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