When this substance is involved, a volcanic eruption can be "phreatic.
Cornelius van Niels proposed that this substance may have been produced as a byproduct of carbon fixing by purple and green bacteria. This substance is found sporadically in the vadose zone. When this substance is involved, a volcanic eruption can be "phreatic." Large-scale movement of this substance is facilitated by thermohaline circulation. When it is removed from belowground, land subsidence can result, as can sinkholes. For 10 points, name this substance whose "fresh" type is contained in aquifers.
Cornelius van Niels proposed that this substance may have been produced as a byproduct of carbon fixing by purple and green bacteria.
water [or H2O; accept various types of water, such as fresh water; prompt on steam]