Wednesday, September 5, 2012

Pyroclastics and an unnamed Procellarum vent

Southern rim of an unnamed vent near Rimae Hevelius. This half-kilometer field of view from LROC Narrow Angle Camera (NAC) observation M137977638R, LRO orbit 5467, September 1, 2010; Resolution 0.5 meters from 45.55 km altitude [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

Today's Featured Image highlights a portion of an unnamed vent (0.80°S,  294.69°E), about 20 km south of Lohrmann D crater, that extends northwest to southeast and parallel to Rimae Hevelius.

The size of this vent is about 12.5 by 3 km.

Due to the surrounding relatively smooth and low albedo materials in this area (see WAC context image below), a volcanic eruption associated with pyroclastic deposits is suspected here.

Zoom out, showing the full 2.1 km width footprint of LROC NAC M137977638R. The blue box outlines the area included in the LROC Featured Image above [NASA/GSFC/Arizona State University].
As seen in the NAC zoom out view (above), there is a sharp boundary between the slope covered by relatively high reflectance materials and the dark, possibly pyroclastic materials at the top of the flat area surrounding the vent. The sharp boundary of the two different layers shows the stratigraphic bedding plane. Other rim portions of this vent were collapsed and the dark materials slid down the slope, so it is hard to recognize the bedding plane.

Estimating the volume of erupted dark material is, in theory, simple. First map the surface extent of the unit and then measure its thickness exposed in the vent wall. However in the opening image, you can see that it is hard to distinguish the actual top of the dark mantle because it has slumped into the vent, blurring the real edge.

In polar orbit, traveling north over western Oceanus Procellarum, Japan's lunar orbiter SELENE-1 (Kaguya) caught this view through it's HDTV camera in 2007. At southwest is the edges of mini-impact basin Grimaldi, with a ridge of highlands between it and the unnamed pyroclastic vent at the center of darker material, above center [JAXA/SELENE]..
Carrying the view further north, the vent can be seen in this simulated view at bottom center [NASA/LMMP/GSFC/Arizona State University].
A NAC DTM (high resolution digital terrain model from NAC stereo images) may provide a better estimate of the layer thickness and thus the volumes, by constructing a three dimensional surface model of the bedding plane. Also the depth, void volume, slope angles, and the layer structures of the vent will help to model the eruption mechanisms, which allows us to understand the ancient volcanic activities on the Moon.

For context, the unnamed vent and surrounding landmarks can are also seen in this LROC Wide Angle Camera (WAC) monochrome mosaic (100 m/pix), centered on 1.13°S, 295.09°E. The blue box outlines of full NAC frame [NASA/GSFC/Arizona State University].
Explore this unnamed volcanic vent by full NAC frame yourself, HERE.

Related Posts:
Pyroclastic Excavation
A Dark Cascade at Sulpicius Gallus
Rima Bode: Constellation region of interest
Alphonsus crater mantled floor fracture
Dark surface materials surrounding Rima Marius

View of the vent from 110 km (LROC NAC mosaic M181594956LR)
View of the vent from 25 km (LROC NAC mosaic M168631915LR)

From the LROC QuickMap , views of two better-known, very similarly shaped vents. Above, at 500 meters resolution, on the southwest side the Orientale basin is the north-south vent at center of the Rimae Focas  formation, with its "smoke ring" of darker material surrounding.  Below, a 16 meter resolution view of the Sulpicius Gallus vent of southwest Mare Serenitatis [NASA/GSFC/Arizona State University].

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