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Head and Gifford (
1980
) provide a qualitative morphological classification
scheme for lunar domes. Their classes 1-3 refer to largely symmetric volcanic fea-
tures resembling terrestrial shield volcanoes, displaying comparably steep flanks
(class 1), flat profiles with relatively steep margins (class 2), and very low flank
slopes (class 3). Domes of class 4 appear close to mare ridges and may have
been formed by intrusive magmatic processes, bending the surface upwards with-
out the eruption of lava on the surface, or may also be structural features, while
class 5 domes are assumed to represent highland terrain over which lava has flown.
Classes 6 and 7 describe small elevated parts of highland surface surrounded by
mare basalt and complex edifices of irregular outline, respectively.
Lunar highland domes are larger and steeper than mare domes. They were formed
of highly viscous, presumably silicic lavas (Wilson and Head,
2003
). Typical ex-
amples are the Gruithuisen and Mairan domes in northern Oceanus Procellarum
(Wilson and Head,
2003
; Kusuma et al.,
2012
) and Mons Hansteen in southwestern
Oceanus Procellarum (Hawke et al.,
2003
).
8.4.2 Observations of Lunar Domes
This section describes spacecraft and telescopic observations of lunar domes, adopt-
ing the presentation by Wöhler et al. (
2006b
) but also taking into account more
recent spacecraft data acquired by LRO and Chandrayaan-1.
8.4.2.1 Spacecraft Observations of Lunar Mare Domes
Most lunar mare domes can only be observed under oblique illumination due to
the low slopes of their flanks. Consequently, the Lunar Orbiter images
4
mostly ac-
quired at solar elevation angles between 20
◦
and 30
◦
display steeper effusive mare
domes, like e.g. some (but not all) of the domes near Milichius (cf. Fig.
8.17
a),
the Hortensius dome field (cf. Fig.
8.17
b), the Marius Hills, the domes in Mare
Undarum (cf. Fig.
8.18
a), and the Mons Rümker complex (cf. Fig.
8.18
b). The
lower domes in Mare Tranquillitatis, however, are invisible in the Lunar Orbiter
images; only some of their summit pits are apparent (cf. Fig.
8.17
c). What is more,
these images are not suitable for photogrammetric analysis aiming for generating
topographic data due to the lack of geometric and photometric calibration; the re-
lation between incident flux and pixel grey value is nonlinear and unknown, be-
cause the images were acquired on photographic film scanned on board the space-
craft.
An orbital Apollo 15 photograph
5
of the large dome complex Mons Rümker sit-
uated in northern Oceanus Procellarum is shown in Fig.
8.19
. It was acquired on
4
Digitised Lunar Orbiter images scanned at high resolution are accessible at
http://astrogeology.
5
Digitised Apollo images are accessible at
http://www.apolloarchive.com
.
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