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Geologic Mapping is a Division C event that returned for the 2019 season. It was previously in rotation from 2014-2016, and was introduced as a trial event in New York in the 2012 season. This event tests competitors' knowledge of structural geology, geologic history, map reading, and related topics.
- 1 Event Overview
- 2 The Event
- 3 Theory Topics
- 4 Example Calculation Problems
- 5 Construction Problems
- 6 External Links
Geologic Mapping requires that students be proficient in both reading and constructing topographic maps, geologic maps, geologic cross sections (usually depicted as layers) and other projections. A working knowledge of Earth history is also necessary, with more in-depth review of tectonics, rock formation, lithologies, and geologic principles. Students should also be able to infer risks of geologic hazards such as landslides, floods, earthquakes, etc. In 2015, the topic of aquifers and underground fluids was added as well. This event can be compared to Road Scholar in Division B, but it is much more advanced.
Geologic Mapping has three types of questions: theory, calculation, and construction. Theory questions can include questions such as "What type of volcano makes up most of the Pacific Ring of Fire?". Students will be required to know data about the geologic time scale. Calculation problems usually involve calculating attributes of a map, such as strike and dip of certain geologic formations. Construction problems require students to draw their own cross sections, use a topographic map to create a profile, use or create a stereonet, etc. Students take a 50-minute test on the topics mentioned above.
This section covers some of the topics covered on theory questions.
One of the major components of this event is geologic maps. Students should be proficient at reading and analyzing geologic maps. For example, here is a geologic map with its accompanying cross section.
The different colors represent different types of rocks and minerals, shown in the legend. Proficiency towards analysis of geographic maps takes practice, as it can be difficult to visualize subsurface structures as they interact with horizontal erosion. The symbols on the cross section refer to strike and dip, a very important concept when reading geologic maps. Below is a diagram explaining strike and dip.
The strike of a fault is the direction that the fault runs. The dip of a fault is the perpendicular of the strike.
There are many other symbols and properties of geologic maps. Information is included in "External Links"
Topographic maps usually consist of concentric rings that show the elevation and other features of a region. In the below image you can see how hills and other higher elevation features have more rings surrounding them. The rings are called "contour lines". Each line represents a certain change in elevation, called a "contour interval". Some problems require first calculating the contour interval by taking 2 elevations, finding the number of contour lines between them, and then dividing.
More extensive analysis of topographic maps can be required, including calculating gradient, finding geologic or man-made features, and assessing geologic risks.
Students should know the basics of plate tectonics, rock formation, Earth structure, and Earth history. Plate tectonics refers to the movement of the plates. Below is an image of all of the plates, as well as their bounding faults. The arrows show what type of fault the plate boundary is (convergent or divergent).
Students should also be familiar with the geologic time scale, which depicts the eras of geologic time and what happened in each era.
Major Geologic Structures
Students should be familiar with major structural elements, such as synclines / anticlines, basins, monoclines, unconformities, domes, and saddles.
Anticlines are the tops of folded rock formations (made that way by compression/ heat), and synclines are the bottoms.
A monocline is a geologic structure in which all layers are inclined in the same direction.
Domes resemble anticlines, but the beds dip uniformly in all directions away from the center of the structure. This forms a dome-like structure. A basin resembles a syncline, but the beds rise evenly from the lowest point. Both have very unique-looking geologic cross-sections, making them relatively easy to identify.
An unconformity, in general, is a gap in the geologic record of a region. There are many types of unconformities.
-A nonconformity is in which sedimentary rocks overlie plutonic igneous or metamorphic rocks
-An angular unconformity in which bedded rocks were tilted and eroded before younger rocks were deposited.
-A disconformity contacts in strata parallel to stratification which may display evidence of non-deposition or erosion.
-A paraconformity is an unconformity in which the separation is a simple bedding plane with no obvious buried erosional surface
Example Calculation Problems
This section goes over several example calculation problems.
The "Three Point Problem"
The 3-Point problem is a common question on tests. It usually involves calculating the strike and dip of a bed of rock and outcrops at 3 points. Below is an example problem.
The solution to this example problem, which may be found on the internet, shows the principles and reasoning behind it.
Calculating True Thickness of a Bed from Map Data
A rock layer shown on a geologic map will appear as a band. The layer is truncated obliquely by the topography and the width will be different from the true thickness. As a result, its sometimes necessary to calculate the true thickness. This page shows an example of one of these problems, and explains several ways to solve it.
Construction Problems include various map-drawing and similar problems. Below are a few examples of somewhat common construction problems.
A common construction problem involves being asked to create a profile of some part of a topographic map. An example can be seen below.
Essentially, a profile is drawn by measuring the distances of each contour line along the plane of the profile, marking each point at the appropriate location along the profile section with the correct height (from the contour level) and horizontal position (from measurement), and connecting the points in a smooth curve.
Profiling a Geologic Map
Occasionally a problem may ask for a profile of a geologic map, which is a somewhat more difficult problem than a topographic profile. The surface of the profile is created exactly like a topographic profile, as detailed above. Determining the subsurface geologic structure will require some interpretation of the map, including recognizing patterns on the surface that indicate the attitude of different rock layers, paying attention to various map symbols that provide relevant information, and using a correlation chart to determine stratigraphy.
A stereonet (in particular, the equal-area Schmidt net) is a tool used in structural geology to plot various structures.
To understand a stereonet, consider an (imaginary) sphere hanging above a flat plane (which is where the stereonet is drawn). All of the structures that are plotted on the stereonet pass through the centerpoint of the sphere, and intersect the circle in some way. The intersections between the sphere and the various structures are projected straight down onto the flat plane, forming arcs for planar structures (or straight lines if they dip at 90 degrees) and single points for linear structures. The stereonet grid itself is composed of various great circles, running in arcs from north to south - essentially the plots of planes with strike of zero degrees (exactly north) and varying dip - as well as small circles that run in arcs from roughly east to west. A piece of tracing paper is placed on top of the stereonet grid and typically attached by a pin in the center, which for a planar structure is then rotated behind the paper to change the strike before plotting at a certain dip (or similarly with the trend and plunge of a linear structure).
In this event, the most common stereonet operations include plotting planar and linear structures (such as bedding planes and lineations), and determining their intersections. The rules allow each team to bring a stereonet and tracing paper to the competition - these will usually fit in your binder without much trouble. A good explanation of how to plot elements on a stereonet can be seen on this site.