Most of the lavas erupted between 17 and 13 million years ago. This photograph shows layered lava flows each 30-50 meters thick at Dry Falls, Washington. The groundwater aquifers are located at the boundaries between individual flows. T he tops of individual lava flows contain abundant holes, called vesicles , which can be filled with water in underground aquifers. Arrows point to some of the largest vesicles.
Water also can flow through cracks and other types of small cavities.
As a result, the water contains essentially no dissolved oxygen . The low carbon-14 and dissolved oxygen contents are not found in water sources near the surface, showing that the deep well water has not been contaminated by shallower water as it is pumped to the surface. Analyses of the well water show that it contains surprisingly high amounts of dissolved hydrogen gas, H 2 and methane, CH 4 . Cultures of the water also demonstrated the presence of several types of bacteria. Prime candidates are pyroxene and olivine , minerals rich in iron and common in basalts.