Article,
VOLCANIC Geology OF HADRIACA-PATERA AND THE EASTERN HELLAS REGION OF MARS
Journal of Geophysical Research-Planets, 98 (E2): 3431--3451 (1993)
Abstract
Hadriaca Patera is a low-relief volcano in the southern highlands
of Mars northeast of the Hellas basin. Layered, friable deposits
composing the extensive channeled flanks of the volcano surround
a well-defined, summit caldera containing late stage eruptive products.
The morphologic characteristics of the channels suggest erosion by
groundwater sapping and surface runoff. The erosional morphology
of the volcano, the lack of lava flow features, and the friable nature
of the flank materials indicate that Hadriaca Patera consists predominantly
of pyroclastic deposits. Gravity-driven flow models demonstrate that
the distribution of flank materials can be attributed to the emplacement
of pyroclastic flows. Both magmatic and hydromagmatic eruption models
are viable: For the magmatic case, the necessary mass eruption rates
(10(7)-10(8) kg/s), ejection velocities (greater-than-or-equal-to
approximately 400 m/s), and volatile contents (approximately 1.5-3.0
wt % H2O) are consistent with parameters derived for terrestrial
Plinian eruptions; for the hydromagmatic case, the required energy
conversion efficiencies are comparable to those of laboratory experiments,
and the inferred permeability of the Martian crust allows large amounts
of groundwater to be transported rapidly (at flow rates of 10(3)-10(4)
m3/s) into the region. Models of cooling during emplacement indicate
that welding of pyroclastic flows can occur at large distances (hundreds
of kilometers) from a source vent on Mars; the layering within Hadriaca
Patera could be attributed to welding of pyroclastic flows that would
control its susceptibility to erosion. Morphologic similarities between
Hadriaca and Tyrrhena paterae suggest a similar volcanic history,
with an early pyroclastic-dominated, shield-building phase followed
by effusive eruptions at their summit calderas and on the flank of
Tyrrhena Patera. The formation of the extensive ridged plains of
Hesperia Planum following the formation of the highland paterae supports
the interpretation of a transition from explosive to effusive volcanism
in the eastern Hellas region. A progressive depletion of volatiles
on Mars is consistent with the morphologic properties of highland
paterae and other central vent volcanoes. A predominance of hydrovolcanic
eruptions in the development of Hadriaca and Tyrrhena paterae would
imply that the transition in volcanic eruption style can be attributed
to a volatile depletion of the crust, whereas magmatic eruptions
at the paterae would be indicative of temporal changes in Martian
magmas.
