| VOLCANIC ERUPTIONS ON IO | ||||
|---|---|---|---|---|
| Plume Number | Name | Location (latitude/longitude) | Height During Voyager 1 Flyby (kilometers) | Activity During Voyager 2 Flyby |
| 1 | Pele | -20°/255° | 280 | ceased |
| 2 | Loki | +20°/300° | 100 | increased |
| 3 | Prometheus | -5°/155° | 70 | increased |
| 4 | Volund | +20°/175° | 95 | no data |
| 5 | Amirani | +25°/120° | 80 | similar |
| 6 | Maui | +20°/120° | 80 | similar |
| 7 | Marduk | -25°/210° | 120 | similar |
| 8 | Masubi | -40°/ 50° | 70 | similar |
Between the two encounters, the volcanic eruption at Loki (P₂) changed character. The single plume emanating from the western end of an apparent dark fissure seen in March was joined by a second fountain of similar size about 100 kilometers to the east. The plume also increased in height, from about 120 kilometers in the Voyager 1 image (left) to 175 kilometers in the Voyager 2 image (right). [260-662A and B]
The detailed structure near the volcano Loki is like nothing seen elsewhere on Io. [260-642B]
When this Voyager 1 picture was taken, the main eruptive activity (P₂) came from the lower left of the dark linear feature (perhaps a rift) in the center. Below it is the “lava lake,” a U-shaped dark area about 200 kilometers across. In this specially processed image, detail can be seen in the dark surface of this feature, possibly due to “icebergs” of solid sulfur in a liquid sulfur lake.
(Bottom) The IRIS on Voyager 1 found this “lava lake” to be the hottest region on Io, with a temperature about 150° C higher than that of the surrounding area.
One model for the structure of Io indicates that an ocean of liquid sulfur with a solid sulfur crust covers most of the satellite. Heat escapes from the interior in the form of lava, which erupts beneath the sulfur ocean. Secondary eruptions in the sulfur ocean heat liquid sulfur dioxide, which is mixed with solid sulfur in the crust. The rapid expansion of sulfur dioxide gas then produces the great eruptive plumes, which consist of a mixture of solid sulfur, sulfur dioxide gas, and sulfur dioxide snow.