Geology Reference
In-Depth Information
Table 7.2. Classi
cation and extent of Martian volcanic features (from Greeley and Spudis, 1981 )
Extent
(10 6 km 2 )
Percentage of
Mars
Type
Example
Characteristics
'
surface
Central volcanoes
Alba
Alba Patera Unique, extremely low-relief shield-like volcano;
sheet and tube-fed
1.13
0.78
ows
Highland paterae
Tyrrhena
Patera
Low-relief, degraded, radially textured volcanoes
0.23
0.16
Shields
Olympus
Mons
Broad, moderate-relief central vent volcanoes;
tube-fed
1.23
0.85
ows
Domes
Tharsis
Tholus
Steeper-sided central volcanoes
0.08
0.05
Total area of central volcanoes
2.67
1.84
Volcanic plains
Simple ows
Hesperia
Planum
Regional plains; wrinkle ridges only; no- (flow-lobes
42.08
29.22
Complex ows
Tharsis
Plains
Complex flow units; flow-lobes abundant; rare
wrinkle ridges
9.16
6.36
Undifferentiated
Northern
plains
Plains of uncertain origin ( (flow-lobes rare),
although probably volcanic
27.37
19.00
Questionable
Aureole
materials
Modi
ed units associated with volcanic units
5.92
4.11
Total area of volcanic plains
84.53
58.69
Total volcanic surface area on Mars
85.20
60.53
Figure 7.12. Tharsis Tholus is a dome volcano of dimensions about
110 km by 170 km and has a large complex caldera at its summit
(NASA Viking Orbiter 858A23).
Figure 7.13. Tyrrhena Patera, northeast of the Hellas basin,
is a central volcano thought to be an eroded ash shield; the
radial features are probably volcanic channels that have been
modi
sensing signatures suggestive of dacite, which could indi-
cate a more evolved magma than basalt.
Highland paterae consist of very low-profile volcanoes
that have calderas, radial flows, and channels (Fig. 7.13) .
fluvial erosion; the youngest features are lavas
erupted from the central caldera, which
ed by
flowed down the channel
to the southwest; the area shown is about 140 km across (NASA
THEMIS mosaic).
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