Is this a petrified sea monster?

As molten rock (lava) flows out from a volcano on the seabed, cool things may happen. Sea monsters may be born! The flowing lava has created a "tunnel" when it flows on the seabed, because the outer rim solidifies, while the lava continues to flow inside. You may wonder how rocks can flow, but remember that the lava is very hot - perhaps 1000° C.