While receiving a Blumpkin the person giving the Blumpkin vomits. This action is like a volcano exploding, sending vomit running down your shaft and balls like liquid hot magma.
Yo, my girl was giving me a Blumpkin last night when she gagged on my meat and turned that Blumpkin into a Blumpkin Volcano!
This requires 3 people. The first person is laying on the floor of a porta potty with porta potty juices in their mouth. The second person poops in the first person's mouth while receiving a blowjob from the third person. The poop splashes on the first persons face. The third person also pukes on the second person's penis. Either the second or third person smears the poop on the first person's face like football facepaint.
"Babe you want a Super Duper Mega Bowl Volcano Blue Bearded Blumpkin with my brother?"
"Yes!"
Sitting down on a toilet and taking a massive shit after eating a volcano crunch wrap, while at the same time, receiving a blow-job.
That's called a volcano blumpkin