Objective – I can learn to identify landforms on the surface of Mars and identify the geological processes that produced them.
Geologic Features of Mars
(source: Activities in Planetary Geology for the Physical and Earth Sciences)
Introduction
In many ways Mars is similar to Earth. There are four geologic processes that shape Earth – wind, water, volcano, and impact. These processes have left their mark on Mars. Volcanism producedlava flows, large shield volcanoes, andplains of volcanic material.
Mars has some of thelargest volcanoes in the Solar System. Olympus Mons is the largest volcano in the Solar System.
Olympus Mons isone of four volcanoes in a region called Tharsis. These volcanoes eruptedrepeatedly over many millions of years. They grow higher with each lava flow. Enormous collapsecalderas are found on the topsof each of thevolcanoes.
Aeolian (wind) is the dominant geologic process actingon Mars today. Landslides and rockslides caused by gravity also change martian geology.
Aeolian (wind) activity is causeserosion. Sand and dustparticles carried by the wind form dunes and windstreaks.
Erosionprocesses involving running water were importanton Mars in the past. Valley systems are found all over Mars. They resemble water-cut valleys on Earth.
A mystery concerning water on Mars is “Where didit go?” Some water probably seeped into the ground. It is frozen there today as ice, and some likelyescaped into space over time. The polarcaps contain some water ice. Mars, like the Earth,has seasons. The polar caps shrink during localsummer and grow during local winter.
There are many features thatshow the surface has been deformed. Stresses can becaused by activities, such as lava flows, that weigh down an area.
Impact craters are found onthe surface of Mars. Craters can be used to determinethe ages of Martian surface materials. Older surfaces have craters which areeroded. Younger surfaces have fewer craters and show less erosion.
You can also estimate age of an area by looking a features. For example, if a valley cuts througha crater, the crater must be older. Individual cratersare worn down over time by erosionand further cratering.
Crispcraters with upraised rims and steep sides areyoung. Less distinct and eroded craters withpartial rims are older. Through a combinationof these principles, the relative ages of geologicfeatures can be determined, and a sequence of geologicevents developed.
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Geologic Features of Mars
Questions and Procedures
(source: Activities in Planetary Geology for the Physical and Earth Sciences)
Examine Figure 11.1: Olympus Mons is a shield volcano 600 km (372.8 mi) in diameter, towering 25 km (15.5 mi) above the surroundingplain. Around its base is a steep cliff as high as 6 km (3.8 mi). It has a summit caldera some 80 km (49.7 mi) wide.
1. Examine the caldera (labeled A) and describe its shape.
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2. Suggest some ways in which the scarp[1] around Olympus Mons might have formed.
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3. Do you think the surface of Olympus Mons is geologically old or young, compared to the surface of theMoon? Explain your answer.
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Examine Figure 11.2: Ius Chasma is part of the western end of Valles Marineris, the largest Martian canyon.Smaller valleys join the main east-west chasm.
4. Which of the four geologic processes might be responsible for the formation of Ius Chasma?
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5. Compare the size of Ius Chasma and its tributaries to the size of the Grand Canyon of Arizona. Which islarger, and by how much?
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Examine Figure 11.3: Valleys west of Chryse Planitia. Similar to some river systems on Earth, these Martianchannels have a branching pattern.
6a. In what direction did the water flow?
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6b. Based on the number and morphology[2] of craters, is this a relatively old or young region of Mars?
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6c. Are the craters you observe older or younger than the valleys? Use the principle of cross-cutting relationsto justify your answer.
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Examine Figure 11.4: The Hesperia region in the southern hemisphere consists of cratered plains whichhave been modified by aeolian processes. Wind-produced features, called bright windstreaks, are associatedwith many craters.
7a. Describe the appearance and orientation of the windstreaks.
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7b. If windstreaks are dust deposits formed downwind from the craters, what wind direction is indicatedhere? (Remember that wind direction refers to the direction from which the wind blows.)
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Examine Figure 11.5: Apollinaris Patera and surrounding region. All four geologic processes can act toshape a planetary landscape. For the following, you will use the knowledge from previous questions to identifyMartian landforms and describe the geologic processes that created them.
8a. Compare Apollinaris Patera (marked A on Figure 11.5) to Olympus Mons (Figure 11.1). How arethey similar, and how are they different?
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8b. What process do you think formed Apollinaris Patera? How can you tell?
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8c. What process do you think formed Reuyl crater (marked B on Figure 11.5)? Justify your answer.
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8d. Ma’adim Vallis is the channel in the southeast part of the photograph, marked C. Which of the fourprocesses do you think formed Ma’adim Vallis? Justify your answer.
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8e. Consider the relationship between Ma’adim Vallis and Gusev, the 160 km diameter crater marked D.What could be the origin of the material that comprises the floor of Gusev? (Hint: the region slopesto the north.)
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9. Based on your observations, what is the probable order of occurrence of A, B, C, and D in Figure 11.5(i.e., which came first, second, third, last)? Give evidence for your answer.
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Geologic Features of Mars – Key
1. It is approximately circular, but has numerousover-lapping craters within it and at the margins.
2. Answers will vary, but should include: a) erosion,b) tectonism (faulting).
3. Geologically young because there are fewimpact craters. Younger than the surface of themoon.
4. Answers will vary. The sharp, straight cliffs andthe large dimensions suggest tectonic processes;the stream patterns on the south side areindicative of modification by running water.
5. Ius Chasma is larger by several times.
6a. Northeast (to the top of the photo).
b. Craters are numerous and degraded, indicatingthis is a relatively ancient region.
c. The craters are older than the valleys whichcut across the center rims. However, there arealso a few fresh, young craters superposed onthe channels, indicating that these impactsoccurred after channel formation.
7a. The diffuse streaks of bright material arefound on the southeast side of craters.
b. The wind blew from the northwest.
8a. Like Olympus Mons, Apollinaris Patera hasradial flow patterns and a basal scarp (cliff).Apollinaris Patera has more craters, a largeflow trending to the south, and a less complexcaldera than that of Olympus Mons. OlympusMons is a much larger edifice.
b. Volcanism, considering its characteristicsdescribed above.
c. Impact formed Reuyl crater, indicated by theejecta pattern and central peak.
d. Gradation by running water, indicated bythe meandering pattern and tributary channels.
e. Water that once flowed through Ma’adimVallis may have deposited sedimentary materialonto the floor of Gusev crater.
9. Answers will vary. D, A (C), C (A), B. D is avery old degraded crater. The flows from Aaremodified at their southern part by sedimentsfrom crater D due to flow of water in channelC. So A preceded C. (This is very difficult tosee and students may reverse the order ofthese two events.) Crater B is fresh in appearance, rim is not eroded, and thus is probablyvery young.
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[1]A very steep bank or slope; a slope or hillside so that it becomes steep, vertical, or steep.
[2] The study of the forms of things.