Publikationsdatum:
2018-10-01
Beschreibung:
The transport and storage of gas within lava domes is critical to their stability or explosivity. To analyze gas flow through these systems, degassing from Volcán Popocatépetl, Mexico, is studied here. Short-duration (hours) passive degassing at Popocatépetl is dominated by oscillating components with periods between 100 and 1,000 s in agreement with similar measurements across a range of other volcanic systems. Over these timescales, porous gas flow through an idealized dome obeys a nonlinear diffusion equation. Approximate solutions contain series of diffusive pressure waves which decay to a steep boundary layer near the dome surface. Wave behavior is governed by the oscillation period and dome rock permeability, acting as a low-pass filter on flux oscillations. This may explain the weakness of higher-frequency (〉0.01 Hz) oscillations in the Popocatépetl degassing data. These waves are shown to significantly modify the dome effective strength. For ∼100-m-radius domes, the pore pressure is comparable to the overburden, and the total strength of the dome is dominated by tensile strength. The pressure in smaller domes (≪100 m) dominates and may induce failure. This may explain observations of extrusion and destruction cycling during dome-producing eruptions. The difference between pore pressure and overburden exhibits a shallow (outermost 5–25%), high-pressure layer which changes in size, shape, and overpressure magnitude throughout oscillations. Linear governing equations assumed by previous studies underestimate the pore pressure distribution and do not capture this shallow layer. Recognition of this layer allows for better understanding of the destabilization or explosion of pressurized lava domes. ©2018. American Geophysical Union. All Rights Reserved.
Print ISSN:
2169-9313
Digitale ISSN:
2169-9356
Thema:
Geologie und Paläontologie
,
Physik
