Origin, history, physical characteristics and tectonic features of Alba Mons - Mars
Introduction
Alba Mons (also known
as the Arcadia ring; formerly and still occasionally known as Alba Patera, a
word that has since been restricted to the volcano's top caldera) is a volcano
in Mars' northern Tharsis region. In terms of area, it is the largest volcano on
Mars, with volcanic flow fields extending for at least a kilometer from its
summit. Despite having a span equivalent to that of the United States, the
volcano barely reaches an elevation of at its greatest point. This is roughly
one-third the height of Olympus Mons, the world's tallest volcano. Alba Mons'
flanks have extremely gentle slopes. The average slope along the volcano's
northern (and steepest) face is 0.5 degrees, which is more than five times
lower than the slopes on the other great Tharsis volcanoes. Alba Mons appears
in wide profile to be a massive but scarcely elevated welt on the planet's
surface. It's a one-of-a-kind volcanic edifice that doesn't exist either on
Earth or on Mars.
Alba Mons has a lot of
distinguishing qualities in addition to its large size and low relief. Alba
Fossae on the volcano's western flank and Tantalus Fossae on the volcano's
eastern flank surround the center portion of the volcano with an incomplete
ring of faults (graben) and fractures. In addition, the volcano contains
unusually long, well-preserved lava flows that radiate outward from the
volcano's center zone.
The massive lengths of
certain individual flows (>) indicate that the lavas were extremely fluid
(low viscosity) and large in volume. Many of the flows exhibit unusual
morphologies, with long, sinuous ridges and discontinuous lava channels in the
center. Water flow likely generated the branching pattern of shallow gullies
and channels (valley networks) between the ridges (especially along the
volcano's northern flank).
Alba Mons includes
among the Tharsis region's oldest and most widely exposed volcanic deposits.
Significant volcanic activity at Alba Mons terminated far sooner than at
Olympus Mons and the Tharsis Montes volcanoes, according to geologic evidence.
Alba Mons' volcanic deposits range in age from Hesperian to early Amazonian
(approximately 3.6 to 3.2 billion years old).
Origin
Name
Alba Patera was the
volcano's official name for many years. Patera (paterae) is a shallow drinking dish or saucer in Latin. The phrase
was coined to describe a group of ill-defined, scalloped-edged craters that
seemed to be volcanic (or non-impact) in origin in early spacecraft
photographs. The volcano was renamed Alba Mons (Alba Mountain) by the
International Astronomical Union (IAU) in September 2007, with the word Alba
Patera reserved for the volcano's two central depressions (calderas).
Alba comes from the
Latin word for white and alludes to the clouds that may be seen from
Earth-based telescopes regularly over the region. The Alba volcanic structure,
also known as the Arcadia Ring, was first found by the Mariner 9 spacecraft in
1972. (about the partial ring of fractures around the volcano). In
1973, the International Astronomical Union (IAU) named the volcano Alba Patera.
When the context is recognized, the volcano is commonly referred to as Alba.
Location
and Size
The Arcadia quadrangle
is centered on Alba Mons (MC-3). The nearby Diacria quadrangle contains a large
portion of the volcano's western flank (MC-2). It covers roughly 2.5 million square
kilometers and has a volume of about 2.5 million km3.
Although Alba Mons
reaches a maximum elevation above Mars' datum, the difference in elevation
between its summit and surrounding topography (relief) on the north side of the
volcano (about) is much greater than on the south side (about) (about ). Alba
spans the dichotomy line between the cratered uplands in the south and the
lowlands in the north, which explains the asymmetry. The volcano's plains slope
northward toward the Vastitas Borealis, which has an average surface elevation
below datum (-). Alba Mons' southern half is built on a large north-south
topographic ridge that correlates to Ceraunius Fossae's broken, Noachian-aged
landscape (pictured left).
Physical
Characteristics
The majority of Alba
Mons' primary building is covered in a coating of dust about a foot thick. In
high-resolution photographs of the top, the dust layer can be seen (pictured
right). The wind has chiseled the dust into streamlined shapes in certain
areas, and minor landslides have slashed it. Some isolated patches of dust, on
the other hand, appear smooth and wind-free.
Since the late 1980s,
several experts have suspected that the beginning phase of Alba Mons
eruptions featured a considerable amount of pyroclastics (and thus explosive
activity). The proof came in the form of several valley networks on the
volcano's northern sides that looked to have been formed by running water. This
evidence, along with thermal inertia data indicating a surface dominated by
fine-grained materials, indicates the presence of an easily erodible substance,
such as volcanic ash. If the edifice was created mostly from pyroclastic-flow
deposits, the volcano's extraordinarily low profile would be more simply
explained (ignimbrites).
Recent data from the
Mars Global Surveyor and the Mars Odyssey spacecraft have found no evidence
that Alba Mons has ever had explosive eruptions. Another theory for the valley
networks on the volcano's north side is that they were formed by the sapping or
melting of ice-rich dust deposited during a recent, Amazonian-aged glacial
period.
In conclusion, the current
geologic investigation of Alba Mons reveals that the volcano was formed by
lavas with basalt-like rheological qualities. If Alba Mons was the site of
early explosive activity, the evidence (in the form of massive ash deposits)
has been mostly hidden by younger basaltic lavas.
Tectonic
Features
The massive labyrinth
of fractures that surround Alba Mons is undoubtedly the volcano's most noticeable
feature. Alba's tectonic characteristics, which include normal faults, graben,
and tension fractures, are almost all extensional. Simple graben are the most
typical extensional features on Alba Mons (and Mars in general). Graben are
long, narrow troughs enclosing a down-faulted piece of crust and connected by
two inward-facing normal faults. Alba boasts the most obvious display of basic
graben on the planet.
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