Tyrrhena Patera
Tyrrhena is the most striking of the highland paterae. It is about 300 km
across, and it has a total relief of about 2 km. The central caldera is
12 km across, but it lies within a larger ring of fractures. This
fracture ring may mark an older, buried caldera. It is 45 km in diameter,
and it encircles the whole summit. The most striking features, however,
are the broad furrows that run away from the fracture ring. These furrows
are up to 200 km in length, and they suggest a period of heavy erosion.
This erosion is very old and likely dates back to the time of volcano
growth. It may mark a time of strong hydrothermal activity. Note that
the furrows east of the summit are buried by a smoother set of volcanic
deposits.
(Part of Viking Orbiter Mosaic 211-5213.)