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MRT to magma chamber: field inquiry on plate tectonics and the rock cycle at Little Guilin, Singapore Field session for SEAGA conference, 29-Nov-2012 Jamie McCaughey Earth Observatory of Singapore, Nanyang Technological University Singapore [email protected] Abstract Little Guilin is probably Singapore's most dramatic and accessible exposure of bedrock, showing two stages of magma intrusion more than 230 million years ago to form plutonic igneous rocks. A short walk away, sandstone of the Jurong Formation is exposed. Through field inquiry, students will make direct observations of the composition, texture, and field relations of these rocks to interpret a geologic history of this part of Singapore. Keywords field inquiry; physical geography; inquiry learning INTRODUCTION Field inquiry approach This site and the suggested questions and activities below provide an excellent opportunity for guided inquiry learning in the field. However, being in the field does not, by itself, ensure that inquiry learning is taking place. In inquiry learning, students pose questions, seek out relevant information, then evaluate the information in an effort to answer the original questions (e.g. Margaret, 2003). In practice, inquiry is guided to varying degrees by the teacher, depending on student prior knowledge, available time, and the complexity of the topic or available information. To promote inquiry learning, answer student questions with guiding questions rather than direct answers (Table 1). Table 1. Possible teacher responses to a student who asks, "What rock is this?" Direct answers (including confirmations of student guesses) inhibit inquiry learning, whereas guiding questions foster inquiry learning. Pedagogy Didactic teaching in the Inquiry learning in the field field Teacher role Teacher as knowledge Teacher as guide and learning coach dispenser Student role Student as knowledge Student as investigator recipient Teacher • It's a norite. • Tell me something about this rock. responses to • It's a norite, which is high • What colour is the rock? the student in iron and cooled slowly • Can you see individual mineral question, underground from a grains in this rock? What is their "What rock magma. size? is this?" • See the coarse mineral • What does the colour tell you grains and dark colour? about the composition of the rock? Look right there. That's • What does the grain size tell you how you know it's a about how this rock formed? norite, and that it cooled • If a rock had a lot of iron, would it slowly underground from be darker or lighter in colour? an iron-rich magma. • If liquid rock cooled slowly, would the mineral crystals grow large in size? • Where would liquid rock cool more slowly - deep underground or on the Earth's surface? Field learning lends itself to an inquiry-learning approach (Mogk and Goodwin, 2012). When the two are combined, students can benefit greatly. Field inquiry helps students critically evaluate simplications and abstractions of natural systems that are presented in textbooks and in the classroom (Stillings, 2012). Field inquiry also helps students to form a more integrated, less compartmentalised understanding of natural systems through both sensory experiences and the process of integrating observations and concepts into a coherent whole (Mogk and Goodwin, 2012). In geography education in Singapore, both the Ministry of Education and National Institute of Education are advocating for field-based inquiry learning to become a standard component of students' geography learning. A key habit for inquiry learning is the practice of separating observations from interpretations. Students might be tempted to leap immediately to the interpretation, "It's granite!" Instead, guide them to start with describing what they see and using that information as evidence to support their interpretations. Cultural history This site is a former quarry. The rocks were cut and blasted out of the ground for use as building stones and other purposes. Student preparation Students should already be familiar with: • The rock cycle • The processes that produce the three rock types (igneous, sedimentary, and metamorphic) • General physical features that distinguish the three rock types • Rocks are made of minerals • Minerals are crystals that occur in a range of sizes • Isostatic adjustment: if significant erosion occurs, the lithosphere rises up in response Logistics The field site is walking distance from Bukit Gombak MRT (Figure 1). As a well-manicured and easily accessible park, the risks are generally low. Students should not climb on steep rocks, enter closed areas, or swim. BUKIT GOMBAK SMRT SITE1 SITE 3 SITE 2 SITE 4 North 0 100m Figure 1. Location of field sites at Little Guilin. (Basemap from streetdirectory.com) SITE 1: OBSERVING AND INTERPRETING ROCKS IN THE FIELD Learning objectives: students will be able to... 1a) Distinguish bedrock from loose soil/regolith. 1b) Distinguish fresh and weathered rock surfaces. 1c) Interpret whether rocks are igneous, sedimentary, or metamorphic Access From Bukit Gombak MRT, walk southeast a few hundred metres on Bukit Batok Ave 5. Pass the "meeting point" sign and enter the park along the main path (at grade, not climbing the staircase.) Continue along the lakefront path about 50 m (Figure 2.) Figure 2. Site 1, looking south. Objective 1a) Distinguish bedrock from loose soil/regolith. Here there are dramatic exposures of bedrock, which in geological terms means solid rock that is physically connected to the rest of the crust. Note that "bedrock" does not mean a particular rock type, only that the rock is connected to the rest of the crust. In contrast, loose soil or regolith sits on top of bedrock but is not physically connected to it. Student questions: • What is bedrock? What is soil? Find, sketch, and describe examples of each. o Guiding questions: Which rock looks like it's connected to rock below the surface? Which rock looks like it is resting loosely upon the surface? o Answer: Bedrock can be seen on the large cliffs across the pond, on the small hill on the near side of the pond, and where the park path crosses over a narrow opening in the rock (Site 2, Figure 1). Soil can be seen as the loose dirt along the top of the cliffs, and also the dirt throughout the grassy areas of the park. The boulders in the grassy areas are not bedrock. • If we break a piece of rock off of the cliff, is it still bedrock? Why or why not? o Guiding questions: How did we define bedrock? o Answer: It would no longer be bedrock, since it is no longer connected to the rest of the crust. However, its composition would not change; if you break a piece of norite off the cliff, it is still norite, just no longer bedrock. • Why is there a cliff here? Why is there a pond here? o Guiding questions: Do you normally find large rock cliffs in Singapore? Do you normally find large boulders laying around in Singapore? o Answer: People dug up and removed this rock in the past to make buildings and other things. This is a former quarry. Objective 1b) Distinguish fresh and weathered rock surfaces. Direct students to look at boulders with varying surface appearances (Figure 3). Figure 3: Weathered vs. fresh rock. The boulders near the bottom have fresher rock surfaces, which are quite close to the actual colour of the rock. The same rock has a different appearance once weathered, as seen in the rocks above and behind. Figure 4: Closeup of a weathered boulder along the park path. Different lichens are seen as orange, a little black, and two shades of green. The blue is spray paint! Student questions: • Some of these boulders have heavily weathered surfaces, which means that chemical reactions and biological activity have modified the surface appearance. Other boulders have fresh surfaces, which are much closer to the original colour of the rock. Which are which? o Guiding questions: If you leave metal outside in the rain over the long term, what happens to it? o Answer: The medium-dark gray boulders are slightly weathered, whereas the boulders with reddish and greenish colours are heavily weathered (Figures 3 and 4). • What are some processes that may have weathered these boulders? o Guiding questions: What does the dark gray colour of the rocks tell you about the amount of iron in the rocks? What might happen to the iron in our tropical climate? Do living things grow on rock or concrete surfaces? o Answer: Oxidation (rust) of iron in the rocks results in red-orange colours. The blackish, green, and some orange colours are lichen. Lichen are a symbiotic relationship of algae and a fungus; the algae photosynthesise sugars, providing food to the fungus, while the fungus secretes acid that breaks down the rock to provide necessary mineral nutrients for life. All of these processes break down the rock and change its surface appearance (Figures 3, 4, and 5). Figure 5: Weathering of rock surfaces. The black colours are lichen; lichen preferentially grow where water runs more frequently down the rock face, hence the streaky pattern on the bottom part of the cliff. Objective 1c) Interpret whether rocks are igneous, sedimentary, or metamorphic Students should already know the rock cycle and general characteristics of the rock types (Table 2). Table 2. The main rock types. Rock type Igneous Sedimentary Metamorphic Common mode of Liquid rock (magma Rock particles A pre-existing rock is formation or lava) cools and (gravel, sand, or changed by heat and crystallises clay) are deposited pressure and later compacted and cemented together Common Mineral crystals are Grains of sediment Mineral crystals align distinguishing interlocking do not interlock; and sometimes characteristics layers might be seen separate into bands of different compositions "It's not the shape, it's what's inside." People tend to focus on the outward shape of rocks.

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