Comparative Geology: Earth and Mars

Summary
The student compares impact craters, shield volcanoes, faults, river deltas, and drainage basin features on Earth and Mars by writing a short paragraph distinguishing the characteristics for each set of features. (3-D glasses needed.)

Background and Theory
Comparative geology is one of the most important methods for decipering the geological history of the other terrestrial planets. In this sense, the study of Mars has been exceedingly rewarding since there are a number of analogous features to those seen on Earth. The features examined in this lab are but a few of these.

Impact Craters
Impact craters are undoubtedly the most common geological features in the solar system. They form by the violent transformation of kinetic energy into thermal energy as the impactor is brought to an abrupt stop at the planet's surface. This figure shows the various parts of a complex crater: basin floor, central peak, terraces, rim, ejecta blanket, and secondary craters. Simple craters lack most of these features, being basically a "bowl-like" depression with a rim and overturned strata.

Shield Volcanoes
Shield volcanoes have a low, broad profile created by highly fluid basalt flows. On Earth, the fluid basalt cannot build up a cone with sides much steeper than 7 degrees. The Hawaiian Islands are composed of shield volcanoes that have built up from the sea floor to the surface some 5 kilometers above. Mauna Loa, if measured from the sea floor, is the world's largest mountain in terms of both height and volume. The volcanoes would be even larger if the Earth's plates stood still.

The shield volcanoes on Mars became much larger because of two important facts: first, since Mars has lower gravity, the volcanoes have less force to keep them low to the ground; second, there are no plate tectonics on Mars, so the "hot spot" forming the volcanoes stays under one area. The incline for Olympus Mons is about 2 degrees (an easy bike ride up in low gear).

Faults
When the movement in a planet's crust is such that they fracture the rock and displace the separated sections, then the resulting structural feature is called a fault. Sometimes faults separate large masses of rock from the surrounding crust and form fault-block mountains. The Sierra Nevada is a westward-tiled fault block. Erosion is gradually modifying the slopes.

The Valles Marineris on Mars is a gigantic split in the crust of the planet, probably brought about by the pressure of the build up of the lava on the Tharsis bulge.

River Deltas
Whenever a river flows into a body of standing water, its velocity and transporting power are quickly stemmed. The debris it carries will gradually build a delta, so named because of the resemblance of the shape to the Greek letter. The stream spreads through the delta in a complex of channels called distributaries.

Drainage Basins
The drainage basin is the entire area from which a stream and its tributaries receive their water. All streams and rivers work to reach their base level. A stream left to itself would erode its bed straight downward, forming a vertically walled chasm in the process. Due to the other agents at work, the cliffs are gradually modified so that they slope away from even the tiniest stream.

The drainage basin on Mars are less defined than those of Earth, leading planetary scientists to believe that drainage of ground water is responsible rather than surface runoff.

Procedure
In general, you may assume that the features on Mars are roughly 10 times their counterpart on Earth. The 3-D images are from the 3-D Tour of the Solar System by Paul Schenk, David Gwynn, and James Tutor. The water pictures are from Views of the Solar System by Calvin J. Hamilton.

For each of the four geologic features -- impact craters, shield volcanoes, faults, deltas, and drainage basins -- write a short paragraph distinguishing what you observe for Mars and Earth. Also note similar features. Observe closely as many details as you can and list a minimum of two differences and two similarities for each set. As an example, your comments may include the steepness of the canyon walls, the shape of the features, the amount of detail seen. Try to use as many of the geological terms introduced above as possible.

Impact Craters (3-D)
Arandas Arandas is an example of a martian crater with fluidized ejecta deposits, a distinguishing characteristic of rampart craters. A thick concentric platform, or pedestal deposit, surrounds the rim. The crater is about 13 km in diameter.

Meteor Crater Meteor Crater formed roughly 50,000 years ago when a 30-meter-wide iron-rich meteor weighing 100,000 tons struck the Arizona desert at an estimated 20 kilometers per second. The resulting explosion exceeded the combined force of today's nuclear arsenals and created a 1.1-kilometer-wide, 200-meter-deep crater.

Impact Craters (3-D)
	Arandas is an example of a martian crater with fluidized ejecta deposits, a distinguishing characteristic of rampart craters. A thick concentric platform, or pedestal deposit, surrounds the rim. The crater is about 13 km in diameter.
	Meteor Crater formed roughly 50,000 years ago when a 30-meter-wide iron-rich meteor weighing 100,000 tons struck the Arizona desert at an estimated 20 kilometers per second. The resulting explosion exceeded the combined force of today's nuclear arsenals and created a 1.1-kilometer-wide, 200-meter-deep crater.

Shield Volcanoes (3-D)
Apollinaris Patera Apollinaris Patera is a complex shield volcano 180 by 280 kilometers across and 5 kilometers high. Apollinaris features an unusually large complex summit caldera 85 kilometers across and 1 kilometer deep, and a basal scarp up to 1 kilometer high. These features resemble those observed on Olympus Mons. A broad-fan shaped volcanic deposit formed on the southern flank.

Mauna Loa The island of Hawai'i rises 9 kilometers above the ocean floor, although only 4 kilometers are visible above sea level. The island is probably the largest mountain on Earth, and consists of five distinct overlapping basaltic shield volcanos. The greatest of these volcanos is Mauna Loa, a classic shield volcano characterized by broad gentle slopes of 4° to 10° that last erupted in 1984.

Shield Volcanoes (3-D)
	Apollinaris Patera is a complex shield volcano 180 by 280 kilometers across and 5 kilometers high. Apollinaris features an unusually large complex summit caldera 85 kilometers across and 1 kilometer deep, and a basal scarp up to 1 kilometer high. These features resemble those observed on Olympus Mons. A broad-fan shaped volcanic deposit formed on the southern flank.
	The island of Hawai'i rises 9 kilometers above the ocean floor, although only 4 kilometers are visible above sea level. The island is probably the largest mountain on Earth, and consists of five distinct overlapping basaltic shield volcanos. The greatest of these volcanos is Mauna Loa, a classic shield volcano characterized by broad gentle slopes of 4° to 10° that last erupted in 1984.

Faults (3-D)
Valles Marineris The canyons of the Valles Marineris form a long series of parallel troughs 3 to 8 kilometers deep. Together, they are long enough to span the United States. This scene features an overview of the western third of the Valles Marineris, from Tithonium and Ius Chasma to western Candor Chasma.

Owens Valley Owens Valley is a large, extensional, fault-bounded trough on the eastern side of the Sierra Nevada Mountains. This valley is part of the Basin and Range structural province, which covers large parts of Nevada and Utah. The Basin and Range was formed when the crust in the western United States was stretched in an east-west direction during the Tertiary period when North America overrode part of the East Pacific Rise (a segment of the Juan de Fuca Ridge).

Faults (3-D)
	The canyons of the Valles Marineris form a long series of parallel troughs 3 to 8 kilometers deep. Together, they are long enough to span the United States. This scene features an overview of the western third of the Valles Marineris, from Tithonium and Ius Chasma to western Candor Chasma.
	Owens Valley is a large, extensional, fault-bounded trough on the eastern side of the Sierra Nevada Mountains. This valley is part of the Basin and Range structural province, which covers large parts of Nevada and Utah. The Basin and Range was formed when the crust in the western United States was stretched in an east-west direction during the Tertiary period when North America overrode part of the East Pacific Rise (a segment of the Juan de Fuca Ridge).

River Deltas
The Betsiboka is Madagascar's main river, flowing for a total of 525 kilometers from north of Tananarive. The river is navigable for at least 130 kilometers inland and the lower reaches pictured here are noted for their extensive rice fields. While the red sediment being transported provides an attractive and informative example of a river estuary, it is a symptom of an ecological disaster for Madagascar. Humans have cleared the island's natural cover of tropical forest so extensively that soil erosion has been vastly accelerated.

MOC2-154 No caption given.

River Deltas
	The Betsiboka is Madagascar's main river, flowing for a total of 525 kilometers from north of Tananarive. The river is navigable for at least 130 kilometers inland and the lower reaches pictured here are noted for their extensive rice fields. While the red sediment being transported provides an attractive and informative example of a river estuary, it is a symptom of an ecological disaster for Madagascar. Humans have cleared the island's natural cover of tropical forest so extensively that soil erosion has been vastly accelerated.
	No caption given.

Drainage Basins
Network These valley networks are less developed than typical terrestrial drainage systems, with the Martian examples lacking small-scale streams feeding into the larger valleys. Because of the absence of small-scale streams in the Martian valley networks, it is thought that the valleys were carved primarily by ground water flow rather than by runoff of rain.

The Republic of South Yemen lies on the edge of one of the world's great sand seas, the Rubh-al-Khali, but even this dry desert region bears the unmistakable imprint of flowing streams and rivers. The branching pattern in the photograph could only have been produced by running water, draining off the surrounding land. These filigree patterns are termed "dendritic drainages" because of their similarity to the way in which trees branch out into progressively finer twigs. The term comes from the Greek dendrites, meaning tree-like.

Diagrams from Leet and Judson, Physical Geology.

	These valley networks are less developed than typical terrestrial drainage systems, with the Martian examples lacking small-scale streams feeding into the larger valleys. Because of the absence of small-scale streams in the Martian valley networks, it is thought that the valleys were carved primarily by ground water flow rather than by runoff of rain.
	The Republic of South Yemen lies on the edge of one of the world's great sand seas, the Rubh-al-Khali, but even this dry desert region bears the unmistakable imprint of flowing streams and rivers. The branching pattern in the photograph could only have been produced by running water, draining off the surrounding land. These filigree patterns are termed "dendritic drainages" because of their similarity to the way in which trees branch out into progressively finer twigs. The term comes from the Greek dendrites, meaning tree-like.