did a volcano actually erupted some how and made the lava flow tunnul

Yes, a shield volcano

Yes. Go to The Lava Beds National Monument where you can obtain all the information on the Lava Beds you could ever want.

Medicine Lake shield volcano lies to the South side of the park and has erupted periodically through the last half a million years. Most of the tube caves in the park were formed by the Mammoth and Modoc craters around 40000 years ago.

Entire chain of volcanic activity fing of fire! Beautiful place!! Well worth the trip!!