Wednesday, April 27. 2011
Volcanic features are observed all over the Moon, but sometimes it is difficult to tell whether an observed feature is of volcanic origin or the remnant of another geologic feature (e.g., basin ejecta or buried rim materials). Today's Featured Image is a prime example of a dome that may or may not be of volcanic origin. The dome is ~1.5 km wide and has a summit crater, but is the crater of impact or volcanic origin? The dome is geomorphologically similar to two volcanoes found in Lacus Mortis. These other domes are about the same size (~1.5 km wide) and have similar appearances, except that today's feature has many more small superposed impacts, suggesting that it is older than the Lacus Mortis volcanoes. Does it mean that this feature in western Oceanus Procellarum is a volcano just because it looks like one? The simple answer is no; but keep reading to find out why.
On Earth, many techniques are used to interpret the geologic history and origin of features in a landscape. Usually, analysis of remotely sensed data and field work are two techniques that scientists use together to unravel the geology for a region. But on the Moon, we can't travel to our favorite geologic feature and commence field mapping and measurements - at least not yet anyway! Instead, scientists need to get creative with the remotely sensed data they have.
LROC NAC stereo images can be used to study the topography of geologic features. Scientists have characterized the topography of larger volcanoes and domes on the Moon, and these data can be used in conjunction with LROC NAC stereo images to measure the dimensions and slopes of the volcano-like feature in today's Featured Image. If the dimensions, slopes, and texture, for example, of a volcano-like feature are consistent with the characterized landforms interpreted to be volcanoes, then it is possible that the volcano-like feature is a volcano. But be careful: just because a volcano-like feature has similar topographic measurements and morphology to other volcanoes does not mean that it is definitely a volcano. Similar to terrestrial field work, scientists studying lunar geology must make sure to look at the "big picture", or the context and regional surroundings, when interpreting remotely sensed images.
The LROC WAC provides a look at the regional, or larger, context of the feature imaged (above). Furthermore, LROC WAC color data can be used to map the variations in color caused by compositional variations. If the color of the volcanic-like feature is the same as that of the Eddington crater rim material, then the feature could be Eddington crater rim material and not a volcano. However, if the colors are different, then there is a possibility that the feature is volcanic in origin - but again, this analysis is not definitive. To reach a more definitive conclusion, you would need to look at the WAC color data for other identified volcanoes or domes and make a comparison. But, of course, sampling the volcano-like feature, in addition to the Eddington rim material and surrounding mare material, would be best!
Take a look at the embayed rim of Eddington crater and this dome and decide for yourself if it formed as a volcano.