Astronomy 330

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Astronomy 330

• Lecture 13

Image from http//cmex-www.arc.nasa.gov/CMEX/inde
x.html
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Astronomy 330 Volcanoes and Tectonics

• Extensive signs of volcanism, northern hemisphere
  is completely covered by volcanic flood basalts
  (we think)
• Huge shield volcanoes, built up by fluid lavas,
  gentle slopes
• They are the largest volcanic structures in the
  solar system

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Astronomy 330 Martian North Pole
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Olympus Mons
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330

• 4 highest volcanoes located in the Tharsis
  region.
• Each of the 3 central volcanoes is about 400 km
  in diameter and all are roughly the same height
• Caldera - crater at the summit of volcano
• Olympus Mons is 700 km in diameter and its volume
  is 100 times greater than any volcano on Earth,
  its caldera shows multiple collapses and little
  erosion, may still be active
• There are many more (100s) of smaller volcanoes
  on Mars as well

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Astronomy 330 Tharsis and its volcanoes
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Caldera of Ulyses Patera Can you
see the differences between the impact craters
and the caldera?
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Olympus Mons again Note its
caldera!
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 More volcanoes (Elysium Mons
Region, note clouds, cone volcanoes)
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330

• Cone volcanoes are also present, but no pancake
  volcanoes like on Venus or composite volcanoes as
  on Earth.
• Tharsis bulge is due to
• Accumulation of volcanic material AND
• Tectonic forces which have uplifted crust
• Extensive fracturing of the surface is seen in
  the surrounding crust of Tharsis, fractures are
  100s of kms long and point away from Tharsis
  center.

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Astronomy 330 tectonic cracks in Tharsis
Start of Vallis Marinaris
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330

• Crater density studies indicate that uplift in
  the Tharsis region began before the formation of
  the Volcanoes. Why ?
• Continents of Venus and Earth result from
  compression forces, on Mars the Tharsis appears
  to be caused by a mantle hot spot.
• As a result Mars is the only planet to have
  volcanoes as its highest mountains.
• Contrast with how highest mountains are formed on
  Earth, Venus, and the Moon. Remember?

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Astronomy 330 See any impact craters on Olympus
Mons?
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Hellas Mounds

• Hellas mounds are unique feature on the surface
  of Mars near the Hellas basin
• Could be volcanic related, subsurface ice melted,
  turned to steam and explosively breaks the surface

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Astronomy 330 Hellas Mounds
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Canyons

• Canyons on Mars are HUGE, Vallis Marineris is 100
  km wide and up to 7 km deep and extends 1/4 of
  the way around the planet
• Not carved by rivers (they dont terminate in a
  low land basin) and have a tectonic originhuge
  cracks in the surface, may be widened by
  landslides and water erosion
• Sides of Canyons show evidence of recent rock and
  mud slides, perhaps aided by the presence of
  water.

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Astronomy 330 All of Vallis Marineris, a canyon
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Closeup of Vallis Marineris
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Coprates Chasma (note layers)
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Amenthes Rupes (note dunes)
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Tithonium Chasma
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Ophir Chasma (note layers,
evidence for avalanches, erosion)
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Martian Volcanism

• Volcanic flows on Mars have many properties
  similar to those seen on Earth in the Hawaiian
  islands
• Individual flows extend for great distances
  indicating low viscosity
• Also rate of flow must have been very large
• Mars does not show river lavas as on Venus
  (maybe yes?)
• Estimates of ages (from crater counts) of
  different flows indicate that volcanic flows
  extended over a long time period on Mars (perhaps
  it is still volcanically active).

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Astronomy 330 Lava flows on Olympus Mons
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Lava flow 100s of km long in
Marte Vallis
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Martian Volcanism

• Individual volcanoes must have been active for
  billions of years, a significant fraction of the
  Age of the Solar System.
• Martian meteorites with a basaltic comp. indicate
  ages of 1.3 billion years
• The large concentration of volcanoes and uplift
  in the Tharsis region is consistent with the idea
  that it is the result of a mantle plume or
  hotspot.
• Mars low surface gravity and lack of plate
  tectonics combine to make Tharsis large and the
  volcanoes there large as well

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Astronomy 330 ALH 84001
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 ALH 84001 close up. Fossil?
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Volcanism today?

• Crater counts indicate that Olympus Mons
  youngest flows are less then 100 million years
• The time between eruptions can be very long,
  millions of years, so it is very possible that
  Mars could still be volcanically active! (More on
  this later)

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Astronomy 330 Channels

• Channels are sinuous valleys and look very much
  like river drainage patterns on the Earth.
• Three types of channels
• Runoff channels
• Drainage channels
• Gullies on canyon slopes
• All are thought to have been formed by running
  water

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Astronomy 330 Outflows and runoff Channels
Outflows shown in red, runoff shown in yellow.
Which would you expect would be older?
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 A runoff channel (Nanedi Vallis)
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 An outflow channel (Kasei Vallis)
Note cratering
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Some gullies
http//science.nasa.gov/headlines/y2000/ast29jun_1
m.htm
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Astronomy 330 Runoff Channels

• Most resemble terrestrial rivers
• Found only in cratered uplands of the southern
  hemisphere and are common here
• Channels consist of simple valleys which are tens
  to hundreds of kms long, occur on steep slopes
• Also, networks of interconnected channels are
  present and common, several hundred kms in
  length, small tributaries merging into a large
  river
• The number of tributaries for channel networks on
  Mars is less than for river systems on Earth

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Astronomy 330 Runoff Channels

• Many tributaries seem to be worn down by
  subsequent erosion
• Channels networks and the fact that they flow
  from higher to lower elevations indicate that
  channels formed by running water
• Tributaries and small channels seem to originate
  from springs, water originated from under the
  surface of Mars.
• Since there are no channels in the northern
  plains and none in volcanic areas, water probably
  carved channels several billion years ago

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Astronomy 330 Runoff Channels

• Crater counts confirm these ages
• Channels formed during the late heavy bombardment
• We also conclude that at this time Mars had a
  much heavier, thicker atmosphere if it had
  running water on its surface

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Astronomy 330 Nigral runoff channel
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Valley network of runoff channels
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Outflow Channels

• These are very large valleys, larger then runoff
  channels
• Confined to the equatorial regions of Mars
• Indicate flow from southern highlands into
  northern plains
• Flow which carved these channels was intermittent
  and catastrophic
• Each major outflow channel is 10 km wide and
  hundreds of kms long
• Characterized by multiple parallel channels which
  diverge and then reemerge along their length

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Astronomy 330 Outflow channels

• Show characteristic patterns of water erosion
• Terraced walls
• Streamlined islands
• Sandbars
• Teardrop shaped islands characterized the mouths
  of outflow channels

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Astronomy 330 Outflow Channels

• All these features of the outflow channels
  indicate that they are the result of massive
  floods
• Estimates of these floods indicate flow rates
  that are a hundred times the rate of flow of the
  Amazon
• Comparable rates on Earth have only been caused
  by catastrophic floods, such as a natural dam
  breaking.

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Astronomy 330 Outflow channels

• Where did all this water on Mars come from to
  produce these kinds of floods ?
• Outflow channels originate in chaotic terrain of
  the southern highlands
• Chaotic terrain is composed of irregular hills
  and valleys
• Since outflow channels extend from heavily crater
  south into lightly cratered northern plains, they
  are younger than the runoff channels

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Astronomy 330 Outflow Channels
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Outflow channels
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Crater islands
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Chaotic Terrain
http//cmex-www.arc.nasa.gov/gallery/index.html
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Astronomy 330 Outflow channels

• Crater counts indicate that outflow channels are
  roughly 3.5 billion years old, also the time when
  Tharsis was starting to uplift
• Theories for origin
• Melting of subsurface ice by volcanic activity
• Chemical release of water from clay material
• Shifting of huge quantities of underground water
  by Tharsis uplift
• There is also evidence that flow continued after
  the initial flood (small rivers in valleys)

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Astronomy 330 Reading

• Go to http//cmex-www.arc.nasa.gov/gallery/index.
  html and click on all the links there. Look at
  the pictures and and read the captions.