Complex sentence: Fort Rock was was originally created when basalt magna rose to the surface and encountered the wet muds of a lake bottom and, powered by a jet of steam, blew molten basalt into the air, creating a fountain of hot lava particles and frothy ash.
Split into simpler sentences: Fort Rock was created when basalt magma rose to the surface and encountered the wet muds of a lake bottom. Powered by a jet of steam, molten basalt was blown into the air, creating a fountain of hot lava particles and frothy ash.