Experimental evidence on the role of gas in sediment liquefaction and mud volcanism

Abstract

Mud volcanoes are structures that are formed through 'cold volcanism' and indicate soil liquefaction. Their evolution depends on the structure, state and excitation of fine-grained feeding sediments. The disturbance of the framework of a loose, fine-grained, saturated sediment causes shear deformation leading to a pore fluid pressure increase. Effective stresses are thereby reduced and can vanish; the soil is then totally liquefied. Small amounts of enclosed gas bubbles render the soil compressible and enhance local shearing, pore pressure build-up and structural damage. Liquefied, overpressurized sediments form mud chambers, whose excess pressure is released through cracks and other inherent weak channels caused, for example, by density variations in the overlying strata.Experiments were conducted on small-scale soil columns and on model slopes, using quartz powder as model material. Soil column tests were aimed at determining the influence of gas bubbles with regard to the liquefaction process, whereas model slope tests were targeted at the collapsability of gentle slopes, subject to atmospheric pressure changes. Different initial porosities were achieved through ion content variation. Liquefaction of fine-grained sediments and subsequent volcano evolution could be produced.

Tectonically-driven mud volcanism since the late Pliocene on the Calabrian accretionary prism, central Mediterranean Sea

“…The existence of intrusive mud chambers at intermediate to shallow depths (<2-4 km) is supported by observations of modern and fossil mud volcanoes as well as by geochemical analyses of erupted fluids (Deville et al, 2003;Planke et al, 2003;Mazzini et al, 2009). Physical modeling suggests the importance of gas in overpressured fluids to promote the liquefaction and fluidization of sediments to form mud chambers, which drive surface activity through a combination of overpressure and buoyancy (Pralle et al, 2003).…”

“…Episodic extrusive activity is also favoured by the dynamics of mud chambers, which are driven in part by internal factors (pressures, buoyancy), as well as by tectonically-driven fluid fluxes (e.g. Deville et al, 2003;Pralle et al, 2003).…”

Earthquake triggering of mud volcanoes

“…Bubbles may also drive other rheological changes. Pralle et al (2003), for example, found that injecting gas bubbles into a suspension of quartz powder promotes liquefaction.…”

Pneumatic fractures in confined granular media

“…In industry, hydraulic fracturing is done to enhance oil and gas recovery [5][6][7], CO 2 sequestration [8], water well and geothermal energy production [9][10][11]. Related natural processes, such as subsurface sediment mobilization, are studied in earth sciences, where sand injectites, mud diapirs, and mud volcanoes are formed due to pore-fluid overpressure [12][13][14][15][16][17]. For example, the Lusi mud volcano in Indonesia is the biggest and most damaging mud volcano in the world [18], having displaced 40 000 people from their homes, and has been active since May 2006.…”