Geologic Mapping

GeoLogic Mapping is a Division C event for the 2015 season. It was introduced as a trial event in 2012, and was an official event for the 2014 season. For the event, students use geologic map skills and knowledge of Earth history to answer questions. Some sections of this article may be based on the 2012 trial event, and therefore may not reflect current rules.

Event Overview

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.

The Event

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.

Theory Topics

This section covers some of the topics covered on theory questions.

Geologic Maps

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

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.

Earth Science

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 here that 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

Construction Problems may involve the use of stereonets. Below are a few examples of problems that have appeared on state / national tests.

Create a Profile of a Topographic Map

One construction problem involves profiling a region given a topographic map, as shown below.

This site details how one would go about creating a topographic profile.

Stereonet Operation

A stereonet is a versatile tool for constructing several geologic elements. This site offers information on how to use stereonets to do many different things.

External Links

Official Trial Rules

New York Trial Rules

Introduction to Structural Geology

Geologic Visualization Tool

Elephantower's Geologic Mapping Resources