In-Class Activity 1_Olympus Mons & Igneous Rocks
Julia Kahmann-Robinson PhD, University of Utah Department of Geology & Geophysics
Recognize a pahoehoe vs. A'a' lava flow through video, explain why the flows differ, and hypothesize which flow might be more common on Mars.
- Pahoehoe lava flow video: http://www.youtube.com/watch?v=qTTLYx4Xo2k&feature=related
- A'a lava flow video: http://www.youtube.com/watch?v=bWswq8PmRII
- Mars lava coils: Discovery news article: http://www.space.com/15446-mars-lava-volcanoes.html
- Have students watch both the Pahoehoe and A'a video (see Resources above in this In-Class Activity). As they are watching, have them record their observations of each flow and how they differ.
- Discuss student observations of these Earth examples and make corrections where necessary.
- Ask students which lava flow, both or neither, would be more common to Mars. Encourage students to substantiate their answers.
- Following discussion of the above, present Figure 1 and ask what type of lava flow is most likely to have formed the spiral feature (see Image File for higher resolution and original image size)
Divide the class into two teams (one Pahoehoe, the other A'a) and give them the basic physical characteristics of the two lava types. Their job is to research (e.g. on the internet) what causes the different physical properties (WHY the two types of lava are different). They should explain how different fluid properties, such as viscosity and crystal and gas bubble content, affects their type of flow. Each team can give a short presentation of their lava.
Below is a brief overview of each lava type:
- Pahoehoe lava- is basaltic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms lava tubes where the minimal heat loss maintains low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into ʻaʻā flows in response to heat loss and consequent increase in viscosity. Pahoehoe lavas typically have a temperature of 1100 to 1200 °C.
- A'a lava- The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an ʻaʻā flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an ʻaʻā flow. ʻAʻā lavas typically erupt at temperatures of 1000 to 1100 °C.
- Accretionary lava balls as large as 3 meters (10 feet) are common on ʻaʻā flows. ʻAʻā is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into ʻaʻā if it becomes turbulent from meeting impediments or steep slopes.
Of the rocks pictured in Figure 2
- Which are most likely to have formed by igneous processes on Earth?
- Which by igneous processes on Mars?
- Make sure students explain their choices in discussion. Hide caption from students. **The .ppt Image File does not have descriptions
Consider the Spirals in Athabasca Valles (Figure 1). Which rock(s) in Figure 2 would you expect to find in Athabasca Valles? Why?
Consider the Spirals in Athabasca Valles (Figure 1), which rock(s) in Figure 2 might be found there?