The early Earth produced somewhat more geothermal heat, before most of the initial heat of formation was dissipated and short-lived radioactive isotopes depleted. This made possible higher temperature Komatiite lava which had a vicosity close to water and flowed rapidly in sheets as thin as 1cm.
The only known volcano in human history to produce carbonatite lava is Ol Doinyo Lengai in Tanzania. The lava is so cold (510 C) that it is black instead of glowing red, and it also flows like water. And there is video of it!
In 2009 the Icelandic Deep Drilling Project struck liquid magma, leading to the first magma-powered geothermal system.
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