Thermal structure and heat loss at the summit crater of an active lava dome

Abstract

Forward-Looking Infrared (FLIR) nighttime thermal images were used to extract the thermal and morphological properties for the surface of a blocky-to-rubbley lava mass active within the summit crater of the Caliente vent at Santiaguito lava dome (Guatemala). Thermally the crater was characterized by three concentric regions: a hot outer annulus of loose fine material at 150-400°C, an inner cold annulus of blocky lava at 40-80°C, and a warm central core at 100-200°C comprising younger, hotter lava. Intermittent explosions resulted in thermal renewal of some surfaces, mostly across the outer annulus where loose, fine, fill material was ejected to expose hotter, underlying, material. Surface heat flux densities (radiative + free convection) were dominated by losses from the outer annulus (0.3-1.5×10 4 s −1 m −2 ), followed by the hot central core (0.1-0.4×10 4 J s −1 m −2 ) and cold annulus (0.04-0.1× 10 4 J s −1 m −2 ). Overall surface power output was also dominated by the outer annulus region (31-176 MJ s −1 ), but the cold annulus contributed equal power (2.41-7.07 MJ s −1 ) as the hot central core (2.68-6.92 MJ s −1 ) due to its greater area. Cooled surfaces (i.e. the upper thermal boundary layer separating surface temperatures from underlying material at magmatic temperatures) across the central core and cold annulus had estimated thicknesses, based on simple conductive model, of 0.3-2.2 and 1.5-4.3 m. The stability of the thermal structure through time and between explosions indicates that it is linked to a deeper structural control likely comprising a central massive plug, feeding lava flow from the SW rim of the crater, surrounded by an arcuate, marginal fracture zone through which heat and mass can preferentially flow.

Volcanic plume vent conditions retrieved from infrared images: A forward and inverse modeling approach

“…Stick-slip events occur 100 to 600 m below the crater (Sahetapy-Engel et al, 2008). One eruption model involves ascent of the mixture of gas and ash up the fracture zone around the plug, to result in an emission from vents distributed around the edge of the vent area (Bluth and Rose, 2004;Sahetapy-Engel and Harris, 2009b).…”

An assessment of hydrothermal alteration in the Santiaguito lava dome complex, Guatemala: implications for dome collapse hazards

“…Current activity at Santiaguito is focused at the Caliente vent (Fig. 1b), where slow lava extrusion and regular Vulcanian explosions occur at the dome summit (Venzke et al 2002(Venzke et al -2012Johnson et al 2004Johnson et al , 2008Sahetapy-Engel et al 2008).…”

“…The summit structure and activity of the currently active Caliente dome is controlled by the slow upward movement of a stiffened plug of dacite in a central conduit leading to both extrusion of a lava flow as well as periodic ash-and-gas eruptions (Bluth and Rose 2004;Johnson et al 2004;Sahetapy-Engel et al 2004;Johnson et al 2008;Sahetapy-Engel et al Sahetapy-Engel and Harris 2008); the structure of the other lava domes has not been well studied. Sapper and Termer (1930a) made early observations of endogenous growth of the dome complex in the 1920s, but multiple dome units and lava flows have erupted since (Rose 1972b;Rose 1987b;Harris et al 2003Harris et al , 2004.…”

Strain‐induced permeability increase in volcanic rock

“…In the event that volatiles cannot escape from such a system, the prospect exists for bubble accumulation or expansion near the surface, allowing pressure augmentation within the conduit and dome and providing the kinetic energy required for explosive dome eruptions [e.g., Sparks, 1997]. Notably, observations of extruding domes highlight the common occurrence of volatile outgassing through faults and fumaroles at their margins [e.g., Johnson et al, 2008;Sahetapy-Engel and Harris, 2009;Lavallée et al, 2013]. Sparks et al [2000] describe the appearance of gas and ash venting between the base of the dome and the neighboring wall rock at Soufrière Hills Volcano, Montserrat.…”