GEOLOGIC MAPPING Superposition

EESA05 Environmental Hazards

Due: Tuesday October 8th before 5pm Drop off completed assignment in one of the EESA05 wooden boxes located outside 511A Among the important tasks in developing understanding of Earth’s history, geologists create detailed maps showing spatial and temporal relationships among different rock units. In this exercise, you will practice developing a geologic map using only relationships of superposition (that is, vertical succession of rock ‘layers’). Fig. 1. Google Earth image of successive lava flows on the north flank of Kilauea volcano, Hawai’i. 1. Open the file ‘Exercise 008 Geologic Mapping-Superposition.kmz’ accompanying this exercise. 2. This view shows a series of successive lava flows on the north flank of Kilauea, an active volcanic vent on the island of Hawai’i. On Hawai’i, a general sense of the relative age of lava flows can be deduced from superposition (i.e. which flows overlie others) and, interestingly, by the color of the flow. 2 3. Fresh basalt flows on Kilauea are typically black. Over time, flows may progress through a series of color changes wrought be progressive weathering of the lava (Holcomb, 1981). As the rock weathers over centuries, iron-bearing minerals hydrate and oxidize, changing the overall appearance of the rocks. A common sequence of color changes is: YOUNG (FRESH) OLD (WEATHERED) Black Dark Gray Brownish-Gray (chocolate) Reddish Brown Tan In addition to somewhat systematic color change, lava flows are often progressively colonized by lichens and higher plants of various kinds related to the degree of weathering and associated availability of ‘soil’ and nutrients (Holcomb, 1981). These plants may also impart a sense of ‘color’ to the rocks when viewed in aerial imagery – though the plants themselves are too small to be resolved, their presence will alter the spectral character (i.e. the color) of individual image pixels. 4. Using these ideas, it is possible to create a relatively simple geologic map of the image you are viewing in Google Earth. Examine the distribution of the placemarks on the image labeled ‘A’ to ‘I’. Use the simple rule above relating lava color to age, with black being youngest and tan being oldest. In the Table below, enter the letter of the placemark in order of increasing age (that is, youngest lava flows at the top of the table and oldest lava flows at the bottom of the table). It is possible on this image to determine which flow overlies others because you may be able to see the terminus of a flow resting on the one beneath. Youngest Flow Oldest Flow 5. Once you have completed labeling that table, turn it in to your TA. 3 LINKS TO RELATED SITES: Wikipedia entry on Kilauea: http://en.wikipedia.org/wiki/Kilauea Hawai’i Volcanoes National Park: http://www.nps.gov/havo/index.htm Hawai’ian Volcano Observatory: http://hvo.wr.usgs.gov/ Kilauea Volcano: http://hvo.wr.usgs.gov/kilauea/ Holcomb, R.T. 1981, Kilauea volcano, Hawaii: Chronology and morphology of the surficial lava flows: Ph.D. Dissertation, Stanford University, Palo Alto, California, USA