blown headgasket....what happened here?
 

This came off my gf's boosted d16y8, Ive never seen this happen. when I took off the headgasket, i noticed there was a bit missing off a part on the gasket, on all 3 layers. but, its on the waterjacket side, not the piston side, what could have caused this?
http://www.we-todd-did-racing.com/we...MXk1NDE%3D.jpg

Re:blown headgasket....what happened here?
 

maybe debris in the coolant system?