Geologic Processes on the Moon/Volcanism - Revision history

Farred: fix typo

2011-11-23T15:24:05Z

fix typo

DDAVIS: /* Domes and Fire Fountains */

2008-11-12T06:38:55Z

Domes and Fire Fountains

Jarogers2001: Volcanism moved to Geologic Processes on the Moon/Volcanism

2008-10-29T10:37:15Z

Volcanism moved to Geologic Processes on the Moon/Volcanism

Jarogers2001 at 23:24, 22 August 2008

2008-08-22T23:24:50Z

Jarogers2001: /* Articles in this Series */

2008-08-22T23:19:45Z

Articles in this Series

Jarogers2001: /* Articles in this Series */

2008-08-22T23:18:26Z

Articles in this Series

Jarogers2001: /* Articles in this Series */

2008-08-22T23:16:07Z

Articles in this Series

Jarogers2001: /* Articles in this Series */

2008-08-22T23:13:54Z

Articles in this Series

Jarogers2001: /* Unusual Features */

2008-08-22T23:13:09Z

Unusual Features

Jarogers2001 at 22:24, 22 August 2008

2008-08-22T22:24:14Z

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−	The first of these are lunar volcanoes, which are called lunar ‘domes’ (not to be confused with volcanic domes on earth, that have steep inclines and different mineralogy). Lunar domes are smooth sided with low levels of incline. This is because lunar lava has such a low viscosity (as noted earlier). Most lunar domes are 5-20 km across, and often have a small pit crater at their summit (fig 8: this is a series of domes near crater Copernicus; note that several have central ‘pits’). Note that a few lunar domes are steep sided, especially in the Marius Hills region, and this ~~offer~~ evidence for changes in the lava’s characteristics—such as cooling and lower rates of eruption. The Marius Hills region contains a large number of lunar domes (fig 9a: earth-based telescope view; fig 9b: Apollo spacecraft view).	+	The first of these are lunar volcanoes, which are called lunar ‘domes’ (not to be confused with volcanic domes on earth, that have steep inclines and different mineralogy). Lunar domes are smooth sided with low levels of incline. This is because lunar lava has such a low viscosity (as noted earlier). Most lunar domes are 5-20 km across, and often have a small pit crater at their summit (fig 8: this is a series of domes near crater Copernicus; note that several have central ‘pits’). Note that a few lunar domes are steep sided, especially in the Marius Hills region, and this offers evidence for changes in the lava’s characteristics—such as cooling and lower rates of eruption. The Marius Hills region contains a large number of lunar domes (fig 9a: earth-based telescope view; fig 9b: Apollo spacecraft view).

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-[[Image:GP4Fig_9a.jpg|thumb|left|Figure 9a<BR/>Marius Hills as viewed from Earth]][[Image:GP4Fig_9b.jpg|thumb|220px|none|Figure 9b<BR/>Marius Hills as viewed from Apollo]]
+[[Image:GP4Fig_9a.jpg|thumb|left|Figure 9a<BR/>Marius Hills as viewed from Earth]][[Image:GP4Fig_9b.jpg|thumb|220px|none|Figure 9b<BR/>Marius Hills as viewed by Lunar Orbiter]]
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 The next features are called ‘dark mantling’ areas.   These were formed by the process of ‘fire fountaining’.  When lava is in the moon’s mantle, it is under considerable pressure.  As it rises to the surface this pressure falls off, allowing gasses trapped in the lava to escape (called degassing).  These gasses—thought to be carbon monoxide or carbon dioxide—act as propellants, shooting the lava high above the lunar surface.   There the lava cools as dark, glassy beads.  Upon falling back to the lunar surface, these beads produce large patches of ‘dark mantling'.  The Apollo missions returned some of these glassy volcanic beads (the first ones identified were dubbed ‘orange glass’).  Visually, these patches appear as large, very dark areas with low crater counts, and occur around basin edges.  Some excellent example can be seen, even in small telescopes, around Mare Serenitatis.
 ==Unusual Features==
 [[Image:GP4Fig_10.jpg|thumb|left|Figure 10<BR/>Hyginus Rille, a possible collapse feature]][[Image:GP4Fig_11.jpg|thumb|Figure 11<BR/>A submerged crater rim visible as a mare ridge]]Finally, there are three unusual lunar features produced by volcanism.  The first of these are endogenous craters, such as Hyginus Rille. These are interpreted as volcanic in origin, and probably formed as collapse features (‘collapse pits’)(fig 10).  Only a return to the moon with further geologic work will fully resolve their origin.  A second unusual feature occurs when a crater is flooded by lava, but after settling (subsidence), the crater rim became visible as a mare ridge (fig 11). A number of these are visible on the lunar surface. <BR/><BR/><BR/><BR/>

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		+	==Domes and Fire Fountains==
	[[Image:GP4Fig_8.jpg\|thumb\|left\|Figure 8<BR/>Domes near Crater Copernicus]]To this point we have discussed the usual schemes for lava filling of the basins, along with the formation of sinuous rilles, arcuate rilles, and mare ridges. Next we need to examine a few other features produced by the volcanic process.		[[Image:GP4Fig_8.jpg\|thumb\|left\|Figure 8<BR/>Domes near Crater Copernicus]]To this point we have discussed the usual schemes for lava filling of the basins, along with the formation of sinuous rilles, arcuate rilles, and mare ridges. Next we need to examine a few other features produced by the volcanic process.

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 *[[Cratering on the Moon]] - First Article
 *[[Tectonic Processes]] - Second Article
-*[[Volcanism]] - Third Article (You Are Here)
+*[[Volcanism]] - Third Article '''(You Are Here)'''

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 *[[Cratering on the Moon]] - First Article
 *[[Tectonic Processes]] - Second Article
-*[[Volcanism]] - Third Article
+*[[Volcanism]] - Third Article (You Are Here)

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 *[[Geologic Processes on the Moon]] - Parent Article
 *[[Cratering on the Moon]] - First Article
-*[[Volcanism]] - Previous Article
+*[[Tectonic Processes]] - Second Article

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	[[Image:GP4Fig_12.jpg\|thumb\|324px\|left\|Figure 12<BR/>Dark Halo craters inside Crater Alphonsus as viewed from earth]]A third unusual feature is the ‘dark halo’ crater. Two types of ‘dark halo’ craters occur, and both are associated with volcanic products. In the type found in Crater Alphonsus, the halos are associated with rilles, and likely represent places of volcanic fire fountaining on the moon (perhaps due to eruptive degassing)(fig 12: earth-based telescope view; fig 13: high resolution image from Ranger IX; note that the areas just around the craters don’t have visible craters, as they’ve been filled in by the volcanic products). [[Image:GP4Fig_13.jpg\|thumb\|230px\|Figure 13<BR/>Dark Halo craters inside Crater Alphonsus as seen by Ranger IX]]Thus it is no surprise that their halos are reminiscent of dark mantling materials. The other type of dark halo crater occur where a bright ejecta blanket covers an older lava flow. When a more recent impact occurs, it pierces the thin veneer of the bright ejecta and unearths the darker lava beneath it. The ejecta from this crater will include those darker materials (an example of this was Crater Shorty, which was visited by the Apollo missions). These can especially be seen in bright ejecta blankets of relatively young craters (fig 14; this one is in the ejecta of Copernicus).[[Image:GP4Fig_14.jpg\|frame\|left\|Figure 14<BR/>A more recent impact within the brighter ejecta of Crater Copernicus]]		[[Image:GP4Fig_12.jpg\|thumb\|324px\|left\|Figure 12<BR/>Dark Halo craters inside Crater Alphonsus as viewed from earth]]A third unusual feature is the ‘dark halo’ crater. Two types of ‘dark halo’ craters occur, and both are associated with volcanic products. In the type found in Crater Alphonsus, the halos are associated with rilles, and likely represent places of volcanic fire fountaining on the moon (perhaps due to eruptive degassing)(fig 12: earth-based telescope view; fig 13: high resolution image from Ranger IX; note that the areas just around the craters don’t have visible craters, as they’ve been filled in by the volcanic products). [[Image:GP4Fig_13.jpg\|thumb\|230px\|Figure 13<BR/>Dark Halo craters inside Crater Alphonsus as seen by Ranger IX]]Thus it is no surprise that their halos are reminiscent of dark mantling materials. The other type of dark halo crater occur where a bright ejecta blanket covers an older lava flow. When a more recent impact occurs, it pierces the thin veneer of the bright ejecta and unearths the darker lava beneath it. The ejecta from this crater will include those darker materials (an example of this was Crater Shorty, which was visited by the Apollo missions). These can especially be seen in bright ejecta blankets of relatively young craters (fig 14; this one is in the ejecta of Copernicus).[[Image:GP4Fig_14.jpg\|frame\|left\|Figure 14<BR/>A more recent impact within the brighter ejecta of Crater Copernicus]]
		+
		+	==Articles in this Series==
		+	[[Geologic Processes on the Moon]] - Parent Article
		+	[[Cratering on the Moon]] - First Article
		+	[[Volcanism]] - Previous Article

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−	*[http://en.wikipedia.org/wiki/Wikipedia:Extended_image_syntax Extended Image Syntax]
−	*[http://en.wikipedia.org/wiki/Wikipedia:Picture_tutorial Picture tutorial]
−	*[http://en.wikipedia.org/wiki/Wikipedia:Gallery_tag Gallery tag]
−	~~{Illustrations pending. This content is currently being adapted by [[User:Jarogers2001\|Jarogers2001]]}~~
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