Introduction to Geology

Introduction to Geology

ASTR 1010L

There are four basic ways the surface of a solid object (a planet, moon, asteroid, or comet) can be modified geologically.

Watch the “Geological Surface Processes” video. What are the four major processes that change the planetary surfaces? Explain how each works and what kinds of features can be formed.

The four major processes are Cratering, Volcanoes, Erosion, and Weathering. Earth experiences many impacts including eruptions, but most craters have been erased by other processes. The craters left by impacting objects can reveal information about the age of a planet’s surface as also its nature and composition at the time the crater was formed. The Earth’s atmosphere and oceans are formed through volcanic outgassing. Volcanism involves the melting of materials within a planet and the eruption and transport of these materials on a planetary surface. For most surfaces the molten material is a silicate-rich fluid. The most common magma on the terrestrial planets is of basaltic composition. A special kind of tectonics, plate tectonics are responsible for shaping the Earth’s surface. Tectonic processes manifest themselves as distinctive morphologic features like faults, fractures, and folds, and the specific characteristics of these features can often be used to infer the local style of deformation that has occurred. Ice, water, and wind drive cause erosion on Earth. Erosion is distinguished from weathering, the physical or chemical breakdown of the minerals in rock. However, weathering and erosion can happen simultaneously.

Let’s examine each of these in turn. Open the “Global Image of Mercury”. What process has most affected Mercury’s surface?

Processes such as solar wind and meteoroid impact affect the surface of mercury. Comets or meteorites may dispose ice in mercury’s surface. Water vapor may also outgas from the planet’s interior and freeze out at the poles of the mercury surface. These process affect the smoothness of Mercury’s surface.

Would you estimate that the surface of Mercury is young or old? Why?

Mercury is about 4.5 billion years old so its surface is most definitely old.

4991100-165513Look more closely at the regions that look like this:

Hypothesize what could make the light streaks coming out from the center of the crater.

The light streaks coming out of the crater could be caused by an eruption. It is more likely that the light streaks is a result of a volcanic eruption.

6638925279414Now look at the “Global Image of Venus”. Zoom in, scroll around, and look for craters. Do you find very many? Note that stripes or rectangles that look like those in the picture to the

right are because a section of Venus was missed when the camera was scanning the surface.

Yes, there are many craters when the ‘Global Image of Venus” is zoomed in. The stripes or rectangular shapes are a result of catering which creates the shapes and the impacts creates the stripes.

If there aren’t very many craters, what surface process do you think would have covered them all up?

If there were no many craters, a volcanic impact could have covered them all up. When volcanism occurs, lava flows and as a result, the craters and faults created during cratering are filled up.

Much of Venus’ surface is covered with lava plains and evidence of tectonic activity. Find what you think is evidence of each of these and either sketch or copy and past part of the picture.

Why does it make sense that volcanic activity and tectonic activity occur in locations close to one another?

Tectonic activity occurs when tectonic plates come into contact and cause friction resulting to faults. Similarly, volcanic activity occurs as a result of high temperatures and pressure beneath the Earth’s crust. These temperature and pressure causes tectonic plates to move and cause tectonic activity.

Venus does have volcanoes in addition to its extensive lava plains, but we’re going to skip on to Mars and look at an example of a shield volcano. The most common volcanoes in the solar system are shield volcanoes, named because they are shaped like a shield placed on the planet’s surface. A computer-simulated view of Olympus Mons, the largest volcano in the solar system, is shown below.

5012690-48315Olympus Mons’ caldera, the location from which the lava flowed, is in the center of the volcano; the other two (smaller) circular features near the top of the volcano are impact craters.

An actual photograph of Olympus Mons is posted on iCollege as well as a topographic image. In the topographic image, the

greens and blues are lower elevations and the reds are higher elevations.

Estimate the height of Olympus Mons above the zero point of the elevation (the average radius of Mars; we use this as a reference height like “sea level” on Earth, but Mars has no sea…).

It has a height of about 20km, or 70,000 feet.

Estimate how far below the zero point the average land round Olympus Mons is. Explain your method; you should come up with a value that is not zero.

It is approximately 634 kilometers of land round. Olympus Mons is one of a dozen large volcanoes, many of which are ten to a hundred times taller than their terrestrial counterparts. The tallest of them all towers 16 miles (25 kilometers) above the surrounding plains and stretches across 374 miles.

Add your two values together to get an estimate of how high Olympus Mons is above the surrounding land.

Convert your value to km.

Measure the length of the scale bar in cm on your display.

Determine the scale of the displayed image: 1 cm = 0.00001 km.

Measure the width of Olympus Mons (not the whole image, just the volcano; it should be pretty easy to see where it begins because for an unknown reason Olympus Mons has a cliff around its base).

Convert your measurement to the actual size of Olympus Mons. Be sure to show your work.

1 cm = 0.00001 km.

Olympus Mons = 634km

634km = 6.34e+7

Answer= 6.34e+7.

Measure the size of the caldera in cm and convert your measurement to km.

Next you are going to construct a scale model of Olympus Mons as seen from the side. To start, let the line below be the base of Olympus Mons.


Based on the height of Olympus Mons you estimated in part c, figure out how tall Olympus Mons is on this same scale. Show your measurements and your work.

It has a diameter of 624 km (374 mi).

25 km (16 mi) high, and is rimmed by a 6 km (4 mi) high scarp.

A caldera 80 km (50 mi) wide is located at the summit of Olympus Mons.

Sketch a side view – correctly to scale – of Olympus Mons using the line above as the volcano’s base. Show the caldera to scale as well.

A Caldera 80 km (50 mi) wide is located at the summit of Olympus Mons.

Before continuing, send a picture of your side view to Dr. Skelton. You don’t have to wait for her to respond before continuing, but do get confirmation you have done this correctly before turning in your lab.

In addition to lots of volcanic activity in its past, Mars also had tectonic activity. Remember that when things – including the interiors of planets – heat up, they expand. Look at the “Global image of Mars”. What do you see that is evidence of extensional tectonics? Draw a sketch.

Evidence of extensional tectonics include craters and faults created in the planet as evident in the image below.

Valles Marineris on Mars is much larger than any other tectonic feature on Venus or Mars. It is so large and so deep, in fact, that early in Mars’ history when there was liquid water on the surface, water flowed in the bottom of it and eroded it.

Ius Chasma, shown up close in an image on iCollege, is part of the Valles Marineris system. The main part of the chasm, running in roughly parallel, mostly straight lines from top center to lower right, was formed by tectonic activity. What evidence of erosion do you see in and near the chasm? Look carefully for two different effects that running water had.

Some of the evidence of erosion include Eos and Ganges are another set of chasmata that contain volcanic or windblown deposits that have slowly eroded over time. Purgatory Chasm is the result of weathering of closely-spaced, quartz filled, ‘joints’ that may mark edges of the Valles Marineris system.

Before continuing on, look again at the small cracks (straight rilles) seen in the upper left of the image. Did the impact crater happen before or after the tectonic expansion? How do you know?

Wrinkles and rilles are evidence that impact crate happened before the tectonic expansion. Wrinkles and riles are as result of cratering. It means that the process begun with small cracks, riles then to wrinkles which created faults and led to shift in tectonic plates and as a result tectonic expansion occurred.

Mars also has wind and therefore wind erosion. Look at the “Curiosity Selfie”. What evidence of wind erosion do you see? (Hint – there are two… One is more basic and may be more difficult to come up with than the other one.) Also – this is a mosaic of 57 images, so the scientist constructing the “selfie” from Curiosity’s images removed the image of the arm holding the camera so it wasn’t distracting.

Ice, water, and wind drive cause erosion on a planetary surface. Erosion is distinguished from weathering, the physical or chemical breakdown of the minerals in rock. However, weathering and erosion can happen simultaneously. Water vapor may also outgas from the planet’s interior and freeze out at the poles of the planetary surface hence causing erosion.

Next we are going to turn to moons of the outer planets, starting with Io. Look at the “Global View of Io” and describe the features you see.

The inner surface of Io is composed of an iron or iron sulfide core and a brown silicate outer layer. giving the planet a splotchy orange, yellow, black, red, and white appearance. Io formed in a region around Jupiter where there is a lot of water or ice. The surface looks icy and windy.

The black features are not craters. In fact, there are no craters at all on Io! What does this tell you about what has happened geologically on Io? Has this happened recently, in the near past, or in the distant? How do you know?

Jupiter’s strong gravity attracted the planetesimals more strongly than Io and thus no crater landed on its surface. Io did have impact craters but they have all been buried in lava flows. This shows that there is no cratering in Io due to lack of gravity.

In fact, all of the black spots on Io are the calderas of active volcanoes. Look again at the image and find at least two locations where the lava is flowing out of the caldera in what look like sinuous rilles in the making. Sketch the lava flows below.

6332220-5414Prometheus is the volcano that is just to the left of the center of the photograph of Io:

In addition to having lava flowing from the caldera, there is also material being

erupted upward. You can figure out the maximum height of the material being thrown from Prometheus by looking at the image below.

75565047855First calculate the scale of the picture. The radius of Io is 1820 km; not all of Io is shown in the image of Prometheus, but the red dashed line shows where the center of Io would be.

1.82e+8 cm = 1820 km

1 cm= 0.0001 km

Next measure the height of the Prometheus eruption in cm, then convert your measurement to the actual number of km using the scale factor.

Measured height in cm: 1e+7 Calculated height in km: 100

What are two reasons you can think of that Io’s volcanoes can spew material so much higher that Earth’s volcanoes do?

The atmospheric pressure in Jupiter where IO is located is high hence the volcanoes will spew material quite higher than on Earth.

Temperatures are extremely high around Io so the volcanoes erupting around this area would be higher that Earth’s volcanoes.

5283836136818The volcanic plume Tvashtar erupts even higher than Prometheus. Use the same method as before to calculate the height of the Tvashtar eruption in km. Show all your measurements and your work – this picture is a different scale so you will need to calculate a new scale! Remember that this picture shows the whole diameter of Io…

Tyashtar erupts 385 kilometers (239 miles) high and covers a terrain as far as 700 kilometers (435 miles) from its center.

1 cm= 0.0001 km.

385 km x 0.00001 = 3.85e+7

Answer = 3.85e+7cm

A different perspective shows a ring around Tvashtar where the erupted material falls back to the ground. Pele is another volcano with a large ring. Draw a sketch of what you think Pele looks like as seen from the side instead of from overhead.


Look at the global view of Saturn’s moon Enceladus. Identify as many geologic features as you can and discuss how you think they would have formed.

Some of the notable geologic features in Saturn’s moon Enceladus include; fissures, plains, corrugated terrain and other crustal deformations also indicate that Enceladus is geologically active. One of the more dramatic types of tectonic features found on Enceladus are its rift canyons. These canyons can be up to 200 km long, 5–10 km wide, and 1 km deep.

Do a Google image search to find pictures of Saturn’s moon Titan, both in visible light and in the infrared.

Describe how this moon looks different in visible light than the other moons you’ve observed.

The lighted side of the Moon faces away from the Earth. he right half of the Moon appears lighted and the left side of the Moon appears dark. During the time between the New Moon and the First Quarter Moon, the part of the Moon that appears lighted gets larger and larger every day, and will continue to grow until the Full Moon.

Describe how this moon looks different in infrared light than the other moons you’ve observed.

Infrared waves, or infrared light, are part of the electromagnetic spectrum. This is caused by the different angles from which we see the bright part of the Moon’s surface. These are called “phases” of the Moon. Of course, the Moon doesn’t generate any light itself; it just reflects the light of the Sun. The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days. The phases always follow one another in the same order.

What explanation can you suggest for the features you see on Titan?

Titan is bigger than Earth’s moon, and larger than even the planet Mercury. It is the only moon in the solar system with a dense atmosphere, and it’s the only world besides Earth that has standing bodies of liquid, including rivers, lakes and seas, on its surface.

Does Titan have erosion? Find images that justify your position and describe what you see.

Due to a network of rivers in Titan, it experiences little erosion.

Is Titan’s surface young or old? What evidence do you have to make this determination?

Titans surface is old due to the presence of wrinkles and rilles are evidence that impact crate happened long time ago. Wrinkles and riles are as result of cratering. It means that the process begun with small cracks, riles then to wrinkles which created faults and led to shift in tectonic plates and as a result tectonic expansion occurred.

Finally, let’s loop back around to Mercury. We have looked at impacts, volcanism, and extensional tectonics, and erosion, but not compressional tectonics. Look at the “Scarp on Mercury”. Sketch what you see that is evidence of the interior of Mercury shrinking. Explain how this feature could have formed.

Cooling in the planet causes mercury to shrink. This slow cooling may drive very recent and even current tectonic and seismic activity on Mercury. This slow cooling drives a very recent and even current tectonic and seismic activity on Mercury.

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