Karst Hydrogeology: A virtual field introduction using Google Earth and GIS
Students will have the opportunity to select and virtually explore the hydrogeology and geomorphology of a karst landscape using Google Earth, lidar data-sourced DEM(s) and geologic maps, and GIS software (QGIS) such that they gain an understanding of karst landscapes and their associated hazards, access to and analysis of internet-based remote sensing data, and verbal and written communication of scientific information.
This basic activity is suitable for use in upper-level undergraduate geomorphology or groundwater hydrogeology courses or as part of a capstone activity for graduating seniors. The main concepts explored are karst geomorphology, karst hydrogeology, Google Earth image interpretation, and basic GIS landscape analysis.
Skills and concepts that students must have mastered
- Familiarity with the concept of karst landscapes
- Topographic map reading
- Previous experience with Google Earth is helpful, but not necessary
- Previous familiarity with GIS is helpful, but not necessary
How the activity is situated in the course
This can be taught as a stand-alone exercise or in conjunction with other modules to build a capstone field experience.
This activity takes about half a day.
Content/concepts goals for this activity
- Visual identification of karst landscapes (particularly in contrast to fluvial landscapes) from aerial imagery.
- Topographic map interpretation to determine drainage patterns.
Higher order thinking skills goals for this activity
- Compare and contrast the ways karst drainage basins behave differently than purely surface stream or porous-media groundwater.
- Integrate digital and analog data.
- Analyze digital and analog data to draw conclusions about landscape-associated hazards.
Other skills goals for this activity
- navigating Google Earth
- searching the WWW and/or USGS's EarthExplorer website
- manipulating data in a GIS for analysis and presentation
- oral presentation or video presentation
- teamwork synchronously and asynchronously
- technical writing
- data management
- personal management
- time management
Description and Teaching Materials
Karst aquifers supply drinking water to 25% of our world's population. It is therefore important that we understand the drainage patterns, potential hazards to humans, and potential threats to water quality that are unique to karst. In this exercise, students select and virtually explore a karst landscape.
Prior to beginning this activity, students need access to an Internet enabled laptop or other device; Google Earth on web, mobile, or desktop; and a GIS (QGIS is a free and open source option). If students cannot access a GIS, please see the Teaching Notes for description of an alternate workflow using only a mobile device. Students may work in groups or independently to complete the activity and presentation. Final reports should be written and submitted independently.
- Central Kentucky Karst, USA
- El Sotano de las Golondrinas, Mexico
- Caverna de Santana, Brazil
- Sof Omar Cave, Ethiopia
- Postojna Cave, Slovenia
- Tenglong Cave, China
- Waitomo Cave, New Zealand
- For an overview of karst aquifers on Earth, students may refer to the World Karst Aquifer Map (WOKAM). A review of WOKAM is attached as a pdf. They can use WOKAM to select an area of interest, browse Google Earth searching for karst landforms, or use one of the links above to go directly to a karst area in Google Earth.
- Once students have selected their focused karst landscape, they need to acquire topographic and geologic map information. For locations in the United States, Earth Explorer is a good source for SRTM DEM files. Students who choose sites outside of the US can still find their DEM data, but will need to do some internet searching to obtain it. A walk-through with screenshots of this workflow for steps 2-5 is available in the Teaching Notes.
- The DEM file then needs to be uploaded to a GIS. For many DEMs, students will need to find the appropriate coordinate reference system (CRS) and reproject their raster. For a review of the Universal Transverse Mercator System, here is a link to the USGS fact sheet and a world map of UTM zones. These two sites are also available attached as pdfs. Another option is to use an interactive online map to help determine the coordinate system for their location. The reproject task is performed by selecting the layer for the DEM raster data. Then click on the "raster" drop down menu. Go to "projections," and select "Warp (reproject)..." Then select a complete path for output and give a name to the output file for the reprojected map data.
- After their project is in the correct CRS, they can then choose a color scheme (right click on the layer > "properties" > "style" > "render type" > "singleband pseudocolor" > "generate a new color map" > select the desired color band > "classify") and make a Hillshade layer to better visualize the topography. To generate a Hillshade layer, again use the "raster" menu. Go to "Terrain analysis" > "Hillshade..." Questions for students: What karst aquifer region did you select? What UTM Zone is this field site in? What colorband worked best for your visualization of the topography? What does the Hillshade function do? How is it helpful?
- This map should now render a more accurate and realistic visualization of the chosen field site. To better understand the drainage patterns of this landscape, extract a set of topographic contour lines. Again use the "raster" menu. Go to "Extraction" > "Contour..." A good interval to start with a 20. If the contour lines end up looking too crowded or too spread out, students can make new contour layers with different intervals. Questions for students: What contour interval did you choose? Why?
- Now that students have detailed topographic maps with contour intervals, they may want to revisit the rule of V's for determining flow paths over land surfaces. This is also attached as a pdf. If students have access to a printer, they can print out a paper copy of the map they built and draw the drainage patterns in with a pencil. There are two digital options for drawing in the water flow paths. For the first, students can export the image of their map in QGIS as png format. To do this they go to the "Project" menu and select "Save as Image..." They can then use a photo editor to draw flow paths on their maps. Students with more GIS experience may want to work directly in the GIS and make new vector layers to create their surface flow paths. Questions for students: Describe the flow paths you drew on your map. What challenges or obstacles did you encounter while determining the routes water would take? What environmental or natural-disaster hazards do you think might be issues in this landscape?
Global distribution of carbonate rocks and karst water resources (Acrobat (PDF) 2.7MB May4 20)
The Universal Transverse Mercator (UTM) Grid (Acrobat (PDF) 29kB May4 20)
Watercourses and ridges on topographic maps: Why the V's? (Acrobat (PDF) 1.2MB May4 20)
Using USGS US Topo Maps and Historic Topographic Maps on your Mobile Device (MP4 Video 84MB May4 20)
Grading Rubric for Karst Intro Activity (Microsoft Word 2007 (.docx) 19kB May4 20)
Intro Karst Hydrogeology Student Handout.docx (Microsoft Word 2007 (.docx) 30kB May15 20)
To complete the full exercise, each student needs an internet-enabled laptop with a GIS software package installed. The instructions given here walk through the use of QGIS, but it is adaptable to ArcGIS. There are additional modifications written in the teaching notes to implement the activity using only a smartphone.
Teaching Notes and Tips
A walk-through for this activity, including screenshots for each step, is included in the uploaded documents.
Intro Karst Hydrogeology Teaching Notes.docx (Microsoft Word 2007 (.docx) 5.9MB May15 20)
Notes on accessibility
All attached files can be accessed from laptop or mobile device. Google Earth works equally well for this activity in desktop, web, or mobile versions. QGIS works best as a desktop download.
As part of this exercise, I want students to experience manipulating DEM data with a GIS. However I realize that not all students have access to a laptop and GIS tools in mobile devices may not offer full functionality. One option for a fully mobile-based activity is to bypass the GIS steps and move straight from Google Earth to accessing a pre-existing Topographic map. Apps are often changing, so there is a legacy issue in promoting specific apps. However, USGS has created a great tutorial video (closed-captioning embedded in the video) for how to access topo maps from a mobile device: https://www.usgs.gov/media/videos/using-us-topo-and-historic-topo-maps-your-mobile-device. For this approach, students would skip steps 2-5, following the procedure in the USGS video (also attached as an mp4). They can then use a drawing app on their device to complete step 6.
"Questions for students" are provided in the activity description. These are to guide students' thinking as they work through the activity. They can then use their responses to the questions as they write their final reports.
Sharing our science:
- After completing the exercise as individuals or as small groups, students share their findings with the whole class. This can happen virtually or in person as circumstances dictate. Each presentation can happen as a slideshow or as a video made by the student(s) and played for the group.
- Each student writes a formally structured report (Title, author's name, date, abstract, introduction, methods, results, discussion, conclusion). Within the report or as a separate document, they should reflect on their experience with this activity and assess their level of understanding before and after the activity of a.) Google Earth, b.) GIS, c.) UTM CRS, d.) topographic map interpretation, and e.) karst hydrogeology.
A rubric to guide the grading of these materials can be found in Supporting Materials.
References and Resources
Background information on karst:
Hands-on supplementary activity if students want to get a 3D feel for the concept of a karst aquifer: https://www.usgs.gov/science-support/osqi/yes/resources-teachers/paper-model-karst-topography.
Background on specific karst areas suggested in Google Earth Links:
- Central Kentucky Karst, USA https://www.usgs.gov/science-support/osqi/yes/national-parks/mammoth-cave-national-park, http://www.igme.es/boletin/2016/127_1/BG_127-1_Art-9.pdf
- El Sotano de las Golondrinas, Mexico https://en.wikipedia.org/wiki/Cave_of_Swallows
- Caverna de Santana, Brazil https://en.wikipedia.org/wiki/Caverna_Santana
- Sof Omar Cave, Ethiopia https://en.wikipedia.org/wiki/Sof_Omar_Caves
- Postojna Cave, Slovenia https://www.postojnska-jama.eu/en/, https://www.slovenia.info/en/stories/karst, https://izrk.zrc-sazu.si/en/predstavitev#v
- Tenglong Cave, China https://en.wikipedia.org/wiki/Tenglong_Cave
- Waitomo Cave, New Zealand https://www.newzealand.com/us/waitomo-caves/, https://en.wikipedia.org/wiki/Waitomo_Glowworm_Caves
Background on the Shuttle Radar Topography Mission (SRTM) to acquire the data used in the DEMs recommended in this activity: https://www2.jpl.nasa.gov/srtm/