Columnar Jointing on Mars
In-Class Activity 2_Olympus Mons & Igneous Rocks
Julia Kahmann-Robinson PhD, Marjorie Chan PhD; University of Utah Department of Geology & Geophysics
Become familiar with the formation, the processes, of columnar jointing and its apparent formation on Mars.
Study Figure 1 above. Write down your hypothesis as to how these igneous rock features formed in two sentences or more. Have you seen any other features on Earth or in daily life that have similar features? Please explain.
View the following cornstarch experiment used to illustrate columnar jointing (Figure 1 (b) is a still from the experiment). Consult the explanation under the video window. http://www.physics.utoronto.ca/~nonlin/movies/starch_movies.html
- Is there perfect similarity between the "real" columnar joints of the Columbia River basalts and the experiment? Why or why not?
- How are the fractures/cracks forming? Are they widening, re-forming through time, starting new fractures?
- What might enhance the cracks? Take a couple guesses.
- How could you foresee such features forming on Mars?
Columnar jointing forms in lava flows, sills, dikes, ignimbrites (ashflow tuffs), and shallow intrusions of all compositions. Most columns are straight with parallel sides (colonnade) and diameters from a few centimeters to 3 m. Some columns are curved and vary in width (entablature). Columns can reach heights of 30 m. The columns form due to stress as the lava cools (Mallet, 1875; Iddings, 1886, 1909; Spry, 1962). The lava contracts as it cools, forming cracks. Once the crack develops it continues to grow. The growth is perpendicular to the surface of the flow. Entablature is probably the result of cooling caused by fresh lava being covered by water. The flood basalts probably damned rivers. When the rivers returned the water seeped down the cracks in the cooling lava and caused rapid cooling from the surface downward (Long and Wood, 1986). The division of colonnade and entablature is the result of slow cooling from the base upward and rapid cooling from the top downward.
View the following discovery, in 2009, on Mars: http://geology.prod-gsw.highwire.org/content/37/2/171
- Referring to the image, about how wide are the columns? (Pay attention to the horizontal scale bar)
- What does this image tell you about igneous rocks and their history on Mars?
- Figure 2 is the original image of columnar jointing captured on Mars using the HiRISE camera for the above discovery. Using arrows, point to where you think the columnar joints are exposed in this terrain.
Figure 2 to the right is the original image of columnar jointing captured on Mars using the HiRISE camera for the above discovery. Using arrows, point to where you think the columnar joints are exposed in this terrain.
Gohering L., Morris, S.W., and Lin, Z., 2006. Experimental investigation of the scaling of columnar joints. PHYSICAL REVIEW 74, 036115, p. 1-12.
Goehring, L., et al., 2008, Nonequilibrium scale selection mechanism for columnar jointing, PNAS, V. 106, p. 387
Goehring, L. and Morris, S.W., 2008, Scaling of columnar joints in basalt, JGR-Solid Earth, v. 113, pp. B10203
Iddings, J.P., 1886, Columnar structure in the igneous rocks of orange Mtn., N.J.: American Journal of Science, v. 131, p. 321-330.
Iddings, J.P., 1909, Igneous Rocks: Wiley, New York.
Long, P.E., and Wood, B.J., 1986, Structures, textures, and cooling histories of Columbia River basalt flows: Geol. Soc. America Bull., v. 97, p. 1144-1155.
Mallet, R., 1875, Origin and mechanism of production of prismatic (or Columnar) structure in basalt: Phil. Mag. v. 4, p. 122-135 and 201-226.
Milazzo et al., 2009 Discovery of Columnar Jointing on Mars; Geology 2009;37;171-174 doi:10.1130/G25187A.1
Spry, A., 1962, The origin of columnar jointing, particularly in basalt flows: Journal of the Australian Geological Society, v. 8, p. 192-216.