Explosion-dominated eruptions .28Pillanian Volcanism.29 Volcanology of Io

galileo images of active lava flows , fountains @ tvashtar paterae in 1999

explosion-dominated eruptions pronounced of io s eruption styles. these eruptions, called outburst eruptions earth-based detections, characterized short duration (lasting weeks or months), rapid onset, large volumetric flow rates, , high thermal emission. lead short-lived, significant increase in io s overall brightness in near-infrared. powerful volcanic eruption observed in historical times outburst eruption @ surt, observed earth-based astronomers on february 22, 2001.

explosion-dominated eruptions occur when body of magma (called dike) deep within io s partially molten mantle reaches surface @ fissure. results in spectacular display of lava fountains. during beginning of outburst eruption, thermal emission dominated strong, 1–3 μm infrared radiation. produced large amount of exposed, fresh lava within fountains @ eruption source vent. outburst eruptions @ tvashtar in november 1999 , february 2007 centred on 25-kilometre (16 mi) long, 1-kilometre (0.62 mi) tall lava curtain produced @ small patera nested within larger tvashtar paterae complex.

the large amount of exposed molten lava @ these lava fountains has provided researchers best opportunity measure actual temperatures of ionian lavas. temperatures suggestive of ultramafic lava composition similar pre-cambrian komatiites (about 1,600 k or 1,300 °c or 2,400 °f) dominant @ such eruptions, though superheating of magma during ascent surface cannot ruled out factor in high eruption temperatures.

two galileo images showing effects of explosion-dominated eruption @ pillan patera in 1997

although more explosive, lava-fountaining stage may last few days week, explosion-dominated eruptions can continue weeks months, producing large, voluminous silicate lava flows. major eruption in 1997 fissure north-west of pillan patera produced more 31 cubic kilometres (7.4 cu mi) of fresh lava on  2 ⁄2-  5 ⁄2-month period, , later flooded floor of pillan patera. observations galileo suggest lava coverage rates @ pillan between 1,000 , 3,000 square metres (11,000 , 32,000 sq ft) per second during 1997 eruption. pillan flow found 10 m (33 ft) thick, compared 1 m (3 ft) thick flows observed @ inflated fields @ prometheus , amirani. similar, rapidly emplaced lava flows observed galileo @ thor in 2001. such flow rates similar seen @ iceland s laki eruption in 1783 , in terrestrial flood basalt eruptions.

explosion-dominated eruptions can produce dramatic (but short-lived) surface changes around eruption site, such large pyroclastic , plume deposits produced gas exsolves lava fountains. 1997 pillan eruption produced 400 km (250 mi) wide deposit of dark, silicate material , bright sulfur dioxide. tvashtar eruptions of 2000 , 2007 generated 330 km (210 mi) tall plume deposited ring of red sulfur , sulfur dioxide 1,200 km (750 mi) wide. despite dramatic appearance of these features, without continuous resupply of material, vent surroundings revert pre-eruption appearance on period of months (in case of grian patera) or years (as @ pillan patera).