When volcanoes erupt, they are not forming cones or any structures. Eruptions create: 1) an explosion, 2) a column of magma blocks down to y=11, and 3) a small pool of lava about 7 blocks across at the "surface" (eg: the ground, the surface of the ocean, or the top of a tree)
(The image above also shows volcanoes with different explosion size settings)
Seen on dedicated server in custom modpack, though I have reproduced it in a single-player test instance with minimal mods.
lavadynamics-1.12.2-5.5.12 forge 14.23.5.2838
When volcanoes erupt, they are not forming cones or any structures. Eruptions create: 1) an explosion, 2) a column of magma blocks down to y=11, and 3) a small pool of lava about 7 blocks across at the "surface" (eg: the ground, the surface of the ocean, or the top of a tree)
(The image above also shows volcanoes with different explosion size settings)
Seen on dedicated server in custom modpack, though I have reproduced it in a single-player test instance with minimal mods.