There are magmas that are not very dangerous, like the black basalts that flow down the sides of Hawaii’s volcanoes. They are very fluid. They do cause damage, but they very rarely cause death because they flow in a slow fashion. Then there are other magmas: those especially rich in silicon and oxygen. They are such stiff and hard magmas that even though they’re in a molten state, they come welling up in a very viscous, very rigid mass. They can flow down the mountain at almost supersonic speeds, killing everything in its path, and are much more dangerous.