Tuesday, January 27, 2009

Boösaule Montes

By popular demand, I thought I would write a blog post about the tallest mountain on Io, Boösaule Montes. Not sure why it is so popular, but you got to give the people what they want...

Boösaule Montes was best seen during the 1979 Voyager 1 encounter with Io but it can also be seen in several global views acquired by Galileo and New Horizons. The image at right is part of a mosaic acquired by Voyager 1 and is the highest resolution images of this feature at around 0.9 km/pixel.

Boösaule Montes, located just to the northwest of the Pele plume deposit, actually consists of not one, but three separate mountains connected by a raised plain. Each mountain displays a unique morphology.

Boösaule Montes "South", seen near the bottom of the image at right, is the tallest mountain on Io. Based on stereo work performed by Paul Schenk et al. 2001, this massif is at least 17.5 kilometers in height. This is more than four kilometers greater than the next tallest mountain on Io, Euboea Montes. The mountain has an irregular morphology, with a relatively gentle slope throughout much of the mountain except for an abrupt scarp on the peak's southeastern margin. According to Schenk et al. 2001, this scarp has a height of approximately 15 km and a slope of 40°. Such a sharp scarp would suggest that a landslide transported some of the mountain's material downslope, but unlike most landslides on Io, the material doesn't seem to have been transported very far from the mountain. Instead, a textured deposit ~3-5 km thick can be seen at the base of the scarp. Based on this morphology, Schenk et al. interprets this sharp slope as a slump scarp.

The mountain is surrounded by a broad plateau that likely represent mass-wasted material, but again, this is oddly absent on the mountain's southwestern margin. On potential sink for material seen at other mountains on Io, paterae, is absent from the immediate surroundings of Boösaule Montes "South". However, to the southwest of Boösaule "South", an old lava flow follows the basal scarp of the mountain. The flow originates from the southern end of a patera (seen at center left in the above image) to the northwest of Boösaule "South". I'm not sure if that's why there is no long-runout landslide deposit in that direction.

Boösaule Montes "North", seen above center in the image at top, is an 8.5-km-tall, dome-shaped mountain with a large fracture running north-south through it. This type of morphology is akin to lava domes on Earth. One possible formation mechanism for this feature is that this mountain sits atop a diapir, created from rising magma in Io's lithosphere. A plateau, perhaps formed by landslide debris, can be seen between both mountains.

The last component, Boösaule Montes "East", seen near upper right in the image at top, is a 7-km tall plateau with two mophologic sections. The western part has a rugged surface with several lineaments running down the length of the mountain. Evidence for mass wasting can be seen along this sections southwestern margin. The eastern part of this mountain has a lower elevation and has a plateau-like morphology. Parts of this plateau have a scalloped margin, suggestive of sapping. Such activity would suggest the presence of sulfur dioxide within some of the layers in the mountain.

Coming up later this week, I will address Io's mountains more generally by looking at some features many of these mountains have in common.

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