In response to the increased level of seismicity, USGS scientists increased monitoring in June. An airborne survey of volcanic gases revealed the presence of magmatic carbon dioxide. Under high pressure deep within Earth's crust, carbon dioxide is dissolved in magma. As magma ascends, the pressure drops and carbon dioxide forms bubbles that separate from the magma. The carbon dioxide, which is far less dense than magma, rises through fractures in the rocks beneath the volcano and escapes to the atmosphere.
Winds then mix and disperse the carbon dioxide.
But because it is heavier than air, carbon dioxide can concentrate in surface depressions in the dome or crater floor, especially under calm conditions, and pose an asphyxiation hazard. Poorly ventilated cavities such as caves in the mass of snow and ice that is accumulating behind the dome could also be hazardous. A network of surveying targets was established on the lava dome, crater floor, and lower flanks of the volcano to detect any ground movements that might occur in response to changes beneath the volcano. No significant movement occurred at any of the targets on the north flank of the dome between the first measurements on June 5 and a follow-up survey on June 29. Additional measurements of survey targets will be repeated periodically for the foreseeable future.