by Christopher L. Fastie, Middlebury College
It seems we spend a lot of time teaching about things that we can’t easily observe, maybe because students are already familiar with processes they see operating around them, or because previous teachers have already harvested those low-hanging fruit. Processes that are obscure because they are small, large, slow, fast, or distant in time or space require more careful explanation. Some of these processes can now be revealed using digital technologies. I used Google Earth to model a very large process that took place 13,500 years ago. I used a global positioning system (GPS) receiver to map a series of glacial features in west central Vermont and transferred the results to Google Earth. I then added graphical models of the retreating Laurentide glacier and associated pro-glacial lakes and rivers which shaped the mapped features. Animated flyovers of the augmented Google Earth surface at different stages of the reconstructed glacial retreat were saved as video files and incorporated into an explanatory video. I have presented this video both before and after student field trips to the study area with good results. Subsequent upgrades to Google Earth allow animated flyovers to be recorded and played back in the free version of the program. This offers a streamlined creation process and the potential for a more interactive and collaborative experience.
Click on the video link below to view.Old, Flat, and Unconsolidated: Salisbury’s Gravelly Past from Chris Fastie on Vimeo.
Science instruction benefits greatly from graphical demonstrations of physical structures and processes. Current textbooks are elaborately illustrated and associated Web sites sometimes include animations of important general processes, but ready-made animations of more specific processes or locally relevant examples are rarely available. Software for producing custom animations is becoming more user-friendly, but the cost and training commitment still prevent wide adoption. Google Earth is a free program that is based on animation of the earth’s surface and that includes tools sufficient for creating simple animations of many social, geographic, geologic, and ecological processes. The professional version (Google Earth Pro), which is not free, adds the capability to save these animations as video files that can be viewed separate from the program.
Geomorphology and Google Earth
Most geomorphic processes, by definition, include movement of material at the earth’s surface, and are therefore well suited for animated representations in Google Earth. Extant geomorphic features can be difficult to observe in the field because they are large, subtle, or obscured by vegetation. Google Earth is an effective way to highlight such features before they are visited in the field, or afterwards when observations can be summarized and interpreted. By animating the time course of development of such features, geomorphic processes and concepts can be effectively revealed.
Glaciers shape the landscape as they flow, but evidence of glacier advance is often obscured by more recent features produced during glacier retreat. The last part of the Laurentide ice sheet to retreat from Vermont was a lobe of ice in the Champlain Valley. As the length and thickness of this lobe diminished, great sediment-laden rivers pouring from the glacier and from the surrounding barren landscape flowed through and alongside the ice. The Champlain Valley drains to the north, and the glacier impounded a temporary body of water called Lake Vermont which rose to a level several hundred feet higher than the current Lake Champlain. Some of the water flowing south into this lake flowed alongside the glacier and built gravelly floodplains between the newly exposed valley walls and the ice. As the glacier continued its retreat, these flat surfaces were abandoned when the river found a lower course next to the ice. Remnants of these surfaces, called kame terraces, are conspicuous features of the Champlain Valley. When the glacial rivers reached the level of Lake Vermont, they built sandy deltas into the lake. These fine-grained deposits were left high and dry when Lake Vermont eventually drained as the impounding ice retreated far enough north.
Modeling Landscape Features
In 1998, I moved into a house at the eastern edge of the Champlain Valley and began to explore the neighborhood. The landscape was dominated by the steep lower slopes of the Green Mountains, but these bedrock slopes were interrupted by dozens of flat, level terraces that appeared to be built of unconsolidated material (sand, gravel, boulders, etc.), instead of solid bedrock. I am a plant ecologist by training, not a geologist, but I began to sketch the extent and location of these flat places to see if the larger pattern held clues to their origin. The sketch maps on paper were a key element of the discovery process because the pattern of the flat areas, which are spread along miles of valley edge, was difficult to see without them. Dense forest covers most of the area and the resolution of the existing topographic maps was insufficient to reveal the subtle terraces. It is possible to identify some of the larger terraces from the air or from stereo aerial photographs, but most terrace margins and their relative heights cannot be discerned well. I assumed that no one had ever mapped these terraces before, so my map would be the first opportunity to study their landscape-level pattern in detail.
The evolving paper map allowed me to begin to reconstruct the progressive positions of the glacier margin and the associated routes of the ice-marginal river that must have created the kame terraces. It required considerable imagination to visualize the massive glacier redirecting a swollen, turbulent river along a hillside that today is three hundred feet above the valley floor. The map was good data, but to explain the complex course of events that played out over many decades and affected many square miles of hillside, it was just a start.
In 2007, I acquired a consumer GPS receiver which had two crucial features. It could produce tracklogs of walking tours by recording location coordinates at ten second intervals and the Garmin Mapsource software it came with had a menu item called “View in Google Earth.” So I could walk the margins of a kame terrace with the GPS recording, upload the tracklog to a PC using Mapsource, and then see the tracklog in Google Earth. Google Earth allowed the terrace margins to be displayed on a recent color aerial photo stretched over the three dimensional topographic surface of the study area. This digital landscape could be viewed from any angle and any height above the surface, and one could “fly” over the scene at will. This encouraged me to make digital tracklogs of all the terraces I had found. Without the tracklogs displayed, the terraces could not be discerned in the crude Google Earth topography, which is just a digital version of the mid-twentieth century USGS topographic maps. As the terraces accumulated in Google Earth, I realized that the animated movie of ice, rivers, deposition, and erosion that had been playing in my mind for several years might be successfully shared with others.
Google Earth incorporates simple drawing tools that allow lines and shapes to be placed on or above the digital landscape surface. Three-dimensional objects can be represented by extending lines from objects down to the ground surface. Far more elaborate 3-D objects can be created using the free program Google SketchUp, but all of the objects created for this project were done with the tools included in Google Earth. I used these tools to trace all the terrace margins imported from Mapsource, creating horizontal polygons in the shape of each terrace. I used the option to extend lines down to the ground surface to give each terrace a solid appearance. The resulting shapes are crude representations of the actual terraces (which do not have vertical sides, and are not all perfectly level) but provide a bold display of the overall pattern formed by the terraces.
I also used Google Earth’s drawing tools to make simple models of the glacier, Lake Vermont, other pro-glacial lakes, and meltwater rivers as I envisioned them at three different times during the formation of the terraces. This allowed the geomorphic features along a four mile stretch of hillside to be put into the context of the retreating ice margin and the associated lateral displacement of an ice-marginal river. I could now display three stages of the landscape process that had shaped my backyard 13,500 years ago.
To bring the process to life, I used the Movie Maker tool in Google Earth Pro to record flyovers of the augmented landscape at different stages in the reconstructed landform-building process. Due to the large scale of the study area there is great explanatory power when the view zooms from the regional to the local and then to a detail, for example, of a river’s route along the glacier. Google Earth allows any view of the digital landscape to be saved by “snapshotting” the view of a saved “placemark.” The program will automatically and smoothly “fly” from one placemark view to another and these single flights formed the content of most of the video clips I produced. A few dozen of these clips were edited together using Adobe Premiere Pro. By inserting cross-fades between identical landscape views depicting different stages in the process, simple animations of the landscape development could be produced.
Presenting the Results
I first presented a draft of the video after students in my class at Middlebury College spent a January day exploring the snow-covered landforms. We made multiple stops to see several key parts of the study area and were still thawing out when we piled into my office to watch the video consisting only of the silent flyovers from Google Earth. I think the students were able to more meaningfully synthesize their field observations after seeing the animated landscape. The reward was probably greatest for those students who had been working hard during the trip to make sense of the individually mundane features. I assume that the video allowed everyone to attach some additional geomorphological significance to the flat surfaces we had visited. During this field trip, we collected some new video of ourselves which was later incorporated into the final version of the video along with other footage and a narration.
For a subsequent class field trip to this area, I asked a new group of students to watch the video beforehand. By this time, a completed twelve-minute version of the video was available online. Viewing the video gave them a context for understanding what they later saw in the field and established a shared baseline of knowledge. I asked students a year later whether viewing the video before or after the field trip would have been more productive and the consensus was that before was better. The primary reason given was that the subject was sufficiently novel and obscure that every explanatory aid was welcome. Viewing the video first also allows a class to quickly address more complex issues such as the relationship between geomorphic origin and vegetation. However, some students recognized that the process of struggling to make sense of confusing field observations has pedagogical value. The video presents a compelling explanatory model, so it eliminates the need for students to assemble and test their own. Waiting until after the field trip to view the video has great potential for classes with the background and motivation to benefit from a puzzle-solving exercise.
In May 2009, Google Earth 5 was released with a new feature that allows flyover tours to be saved and played back within the program. The tour is not saved as video, but as a set of instructions that the program interprets in real time. While creating the tours, drawn objects (e.g., rivers or kame terraces) can be toggled on or off, creating simple animations. Photographs or videos can be displayed sequentially at designated places in the landscape. Narrations or music can be created and saved with a tour. This new feature offers an alternative method of sharing explanatory flyovers and animations.
Learning to save and distribute tours is easier than learning to save video clips and produce online videos and can be done with the free version of Google Earth. Without programming, tours can be embedded on Web pages where they play automatically in a window. The window is a working instance of Google Earth, so if the tour is stopped the user can interact with the digital landscape without having Google Earth installed (a free Google Earth browser plug-in is required). Tour files can also be distributed directly to users who can interact with them using Google Earth. The keyhole markup language (KML) files which encode the tours are usually small and easy to distribute to others. In addition to watching the recorded tour, users with Google Earth installed can experiment by toggling features on and off or creating their own new features. This creates the opportunity for interactive and collaborative projects. An advantage of KML tours over tours saved as video files is that it provides a view of the full resolution Google Earth landscape, not a compressed video version, and displays the most current aerial photos. Soon after I completed the video about glacier features, Google Earth updated the photo coverage of Vermont with higher quality, more recent images, instantly changing the video’s status to outdated. A primary disadvantage of distributing KML files to others is that there is less control over the viewing experience, which depends on the user’s operational knowledge of Google Earth, and settings in Google Earth (and of course, Google Earth must be installed). For examples of the tours I created, see www.fastie.net. You can also download the .kmz file for viewing in Google Earth.
Learning to view the landscape in Google Earth is fun and easy. Learning to produce and save video clips or KML tours is more of a challenge. Google’s online help and tutorials are a start, but you should plan for some trial and error if you want to produce something other than the simplest result. If there is someone on your campus who can help you get started, you might be able to climb the steepest part of learning curve in an hour. Otherwise, plan for some additional learning time. Although the required commitment is not trivial, the models and tours you create can be used year after year to give students valuable insight into geographic patterns and processes that no one has witnessed firsthand.