lava tube with high CO2

lava tube with high CO2
Originally uploaded by Asia Trip2007.

This particular lava tube has amazingly high CO2 inside so you have to be careful when you go in. Our guide used a lighter. The lighter had no problems igniting at mid height, but down near our feet it wouldn't ignite (CO2 is heavier than O2 so it remains lower) so the cave was okay to enter for the time being. We tried guessing what might've caused such high concentrations of CO2 in this cave but came up short. This is when our guide showed us the culprit, and it won't be what you are expecting.
Tree roots. The roots had perforated the ceiling of the lava tube and some dangled several meters down. But just as trees create O2 above the surface, supplying us with the needed Oxygen we survive on, below the ground the reverse is in action. CO2 is expelled from the roots but because there is no earth to mix it with other elements, the CO2 just saturates in the lava tubes.... Strange...