Abstract
Crustal stress field can have a significant influence on the way magma is channelled through the crust and erupted explosively at the surface. Large Caldera Forming Eruptions (LCFEs) can erupt hundreds to thousands of cubic kilometres of magma in a relatively short time along fissures under the control of a far-field extensional stress. The associated eruption intensities are estimated in the range 109 - 1011 kg/s. We analyse syn-eruptive dynamics of LCFEs, by simulating numerically explosive flow of magma through a shallow dyke conduit connected to a magma chamber that in turn is fed by a deeper magma reservoir, both under the action of an extensional far-field stress. Results indicate that huge amounts of high viscosity silicic magma can be erupted over timescales of a few to several hours. Our study provides answers to outstanding questions relating to the intensity and duration of catastrophic volcanic eruptions in the past. In addition, it presents far-reaching implications for the understanding of dynamics and intensity of large-magnitude volcanic eruptions on Earth and to highlight the necessity of a future research to advance our knowledge of these rare catastrophic events.
Highlights
There is compelling evidence that Large Caldera-Forming Eruptions (LCFEs) are characterized by extremely large intensities
Most LCFEs occur in both subduction zone and extensional environments characterized by relatively low rates of magma production implying that the thousand km3 volume magma chambers feeding those events have to accumulate over long periods (>105 years; Jellinek and De Paolo, 2003)
The effect of the far-field extensional stresses is shown in Figure 2 where we reported the profiles of the tensile stress, σt, along the vertical axis of the shallower dyke conduit for both an unpressurized magma reservoir and for a magma reservoir with 10 MPa overpressure
Summary
There is compelling evidence that Large Caldera-Forming Eruptions (LCFEs) are characterized by extremely large intensities. Magmas stored in relatively shallow chambers (3–8 km; e.g., Smith et al, 2005, 2006; Matthews et al, 2011; Chesner, 2012) normally have to overcome critical overpressures up to ∼50 MPa for nucleating new fractures and up to ∼10 MPa for propagating magma up to the surface (Rubin, 1995; Jellinek and De Paolo, 2003). In some cases there is clear evidence of new injection of magma (and associated oversaturation of volatiles) as main cause to achieve the required overpressure to open the magma chamber (e.g., Sparks et al, 1977; Pallister et al, 1992; Self, 1992; Folch and Martí, 1998). In the case of tectonic triggers, the magma chamber would evacuate the magma through the pre-existing faults or newly formed fractures without needing any over-pressurization of the magma chamber (Martí et al, 2009)
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