Tadpole and Lava Tube (NAC DTM)

An irregularly shaped depression, resembling a tadpole, first and largest in a sinuous chain of pits. A 14.4 km field of view from LROC Narrow Angle Camera-derived Digital Terrain Model (NAC-DTM) of the tadpole-shaped start of the informally named "Gruithuisen K Sinuous Rille chain" complex in north central Oceanus Procellarum. Color shaded-relief depicts elevation derived from photo-interferometry based on four LROC Narrow Angle Camera observations and resulting in an array of highly granular practical data, packaged into LROC NAC DTM PITVENT; higher elevations are red and white, lower elevations are blue and purple [NASA/GSFC/Arizona State University].

J. Stopar

LROC News System

Today's feature is an irregularly shaped, steep-walled mare depression that looks a bit like a tadpole; it is about 8 km long and located at the northwest end of a 60-km long, sinuous chain of pits (35.284°N, 315.901°E) northwest of Gruithuisen crater.

The pit chain was one of the first and most spectacular candidates proposed for an intact lunar lava tube (i.e., one with uncollapsed segments).

This depression may be the source vent for the lava flows that host the pit chain (see image below).

The unnamed first among many candidate features surveyed for hints of underground voids, lava tubes, etc., west of Gruithuisen K crater in north central Oceanus Procellarum. LROC WAC mosaic swept up over three sequential orbits July 12, 2011; 77.2° incidence, resolution 57.9 meters from 42.5 km [NASA/GSFC/Arizona State University].

Volcanic vents tend to be sub-circular or elongate, like today's feature, which is roughly 600 meters deep and has steep inner walls (~35° slopes). Similarly sized and shaped features include examples near Sulpicius Gallus crater and the Orientale basin. Dark, low-albedo, materials surrounding the Sulpicius Gallus and Orientale features suggest formation through explosive pyroclastic eruptions; however, further exploration is still needed to confirm this interpretation.

Collapse pits, with sharp and nearly vertical walls, like the one in the Marius Hills (shown in a previous post) suggest fairly recent collapse of ancient lava tubes. The chain of pits near Gruithuisen, however, has more subdued topography, and likely formed earlier in the history of the Moon (perhaps more than 1 or 2 billion years ago).

An early mission Commissioning LROC NAC observation, covering a cross-section of the sinuous depression chain. LROC NAC M102443238LR, LRO orbit 272, July 17, 2009; incidence angle 77.85° at 1.54 meters resolution, from 155.56 km over 35.47°N, 316.56°E [NASA/GSFC/Arizona State University].

Intact lava tubes have long been thought to be important to future exploration. Many have speculated that uncollapsed portions of lava tubes could be used to shield explorers from harmful radiation, as well as provide a relatively warm and stable environment that is buffered from the large temperature variations at the surface.

Many hope that uncollapsed lava tubes will be located near volcanic materials that can be used in construction or energy-generation processes. However, we still have not explored inside any lava tubes on another planet, though many engineers and scientists are currently working to enable such activities. In the meantime, LROC images combined with other data sets, can be used to search for additional lava tube candidates.

Explore today's tadpole-shaped vent in more detail: LROC NAC M1103837710.

Continue Reading about this fascinating lava tube candidate and the sinuous pit chain, or explore the Sulpicius Gallus vent and Orientale Basin vent in more detail.

Even more to explore:

Collapsing Tube

Pit craters in NAC DTM topography

Pyroclastics and an unnamed Procellarum vent
Source vent for Rima Prinz I
Craters on the Schrödinger pyroclastic cone
Morphology and distribution of volcanic vents in the Orientale basin from Chandrayaan-1
Unassuming volcanic vent north of Aristarchus Plateau
New pyroclastic structures identified using LROC data
A dark cascade at Sulpicius Gallus
Hyginus and pyroclastics
Layer of pyroclastics in Sinus Aestuum
Lavoisier Pyroclastics
Pyroclastic Excavation
Pyroclastic Trails
Pyroclastic Vent at Orientale DTM

A tortuous path in Posidonius

This may look like a work of abstract art, but in reality, it's for science! This colorful image is an LROC slope map of the northwestern portion of the floor of Posidonius crater. Warmer colors indicate steeper slopes, whereas cooler colors are shallower slopes. A rille winds its way across the floor and flows along a southerly course, diverging from its path along the crater rim. A tributary rille can be seen joining the main rille at the bottom center. Image width is approximately 5.5 km. North is up [NASA/GSFC/Arizona State University].

H. Meyer
LROC News System

Sinuous rilles, such as the one above, form through the flow of hot, turbulent lava.

Rilles can be found in many locations across the lunar surface and two very different mechanisms are generally thought to form them.

Mechanical erosion refers to the physical removal of material by the lava flow, similar to how rivers erode channels on Earth.

Alternately, some lavas are so hot that they partially melt the substrate, and deepen the channel through time. These processes on there own would both result in downcutting into the surface, but they were often simultaneously working to reshape the lunar surface.

Posidonius (95 km, 31.878°N, 29.991°E) exhibits several rilles of differing types, seen below (linear and sinuous).

The vicinity of the northwest quadrant of Posidonius (95 km, 31.878°N, 29.991°E) has to have been imaged at high-resolution from more than one angle to enable interferometric determinations and to create the LROC NAC-derived Digital Terrain Models. Above the same general vicinity was imaged with spacecraft (and camera) slewed 59.03° from orbital nadir. LROC NAC observation M1096379115L, LRO orbit 13941, July 8, 2012; 82.31° sunset incidence, resolution 4 meters, from 145.49 km over 32.37°N, 17.41°E [NASA/GSFC/Arizona State University].

Posidonius is a 95 km diameter crater on the northeastern margin of Mare Serenitatis. The floor of Posidonius exhibits a number of interesting geologic features. In the western portion of the floor, the sinuous rille from Today’s Featured Image winds its way through smooth plains that partially bury the crater wall.

LROC NAC M1098658474R, LRO orbit 14260, August 3, 2012; 53.15° incidence angle, resolution 1.45 meters, from 143.74 km over 32.04°N, 28.43°E [NASA/GSFC/Arizona State University].

In the eastern portion, the floor is fractured and tilted, similar to craters like Karpinskiy, creating a cliff that drops ~ 1 km to the smooth floor. When compared to the highlands, Posidonius has few craters superposed on its floor, like Posidonius A (11 km) & C (3.5 km), indicating that the floor of this crater is younger.

Huge reduction of the full-width mosaic of both the left and right frames from LROC NAC  oblique observation M1096379115L. Area shown at full resolution further above, boxed in white [NASA/GSFC/Arizona State University].

Check out the full slope map HERE.

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Kink in Rima Krieger
An observation post on the rim of Posidonius
Rimae Posidonius
Truncated rille in Jules Verne
Posidonius Y
Meanders in Posidonius
NAC DTM Posidonius