When a cock is inserted into an anus as a solid turd is egressing. The cock must split the turd hot-dog style for it to qualify as a "log splitter." Otherwise, it is known as an Alaskan Coal Miner.
"Yo dawg, I rammed this girl so hard last night, I gave her the Alaskan Log Splitter!"
A sexual act during which the woman's legs are held by the ankles and spread as far apart as possible, while ramming the cock into her with as much force as possible, making the woman fear she will be split in half.
If the act is performed correctly, the fuck profile should perfectly imitate the piston-action of a real log splitting machine.
"Hey Chris, Sherry was complaining all day at work that she was sore and could hardly walk...what did you do to her last night?"
"Well, she was talking shit about how much cock she could handle last night, so I put her ass in the log splitter until she started spraying female ejaculate all over the place in an uncontrolled fuck quiver."