Name: ______________________
Date _______
Earth Science
Period: _____
Lab # 24: Mapping a Mudslide
Fig 1: Tully Valley Mudslide of 1993
Figure 2: Tully Valley
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Background
A landslide--part of a slope breaking away through gravity--is typically associated with periods of heavy rain
and/or large amounts of melting snow. Areas that have been burned by fire have an increased risk of landslides,
due to increased soil exposure to infiltrating water. Flooding, which is a major concern during heavy rain and
snow melt, can become worse when a landslide blocks paths for water to run off.
A mudslide is the rapid movement of a large mass of mud formed from loose dirt and water. It is a type of fast
moving landslide or debris slide. Mudslides usually start on steep hillsides as shallow landslides that liquefy and
accelerate to speeds that are typically about 10 miles per hour, but can exceed 35 miles per hour. Gravity is the
force driving landslide movement. Factors that allow the force of gravity to overcome the resistance of earth
material to landslide movement include: saturation by water, steepening of slopes by erosion or construction,
alternate freezing or thawing, earthquake shaking, and volcanic eruptions. The consistency of debris flow
ranges from watery mud to thick, rocky mud that can carry large items such as boulders, trees, and cars.
Fig 3: Components of a debris slide
Source area
Depositional area
Problem: How can you use a drawing based on a topographic map to infer how the Tully Valley
Landslide occurred?
Materials: Slip of paper, map of Tully Valley markers, pencil
Procedure
1. Color in the Tully Valley floor in green on figure 2. Outline the Onondaga Creek in blue. Color the brine
fields in brown or tan. (refer to diagram on Smart Board for assistance).
2. Using the map key and your slip of paper, measure and record the length and width of the Tully Valley
in kilometers.
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Length: _______________
Width: ________________
Data Analysis
Answer in complete sentences!
1. What were the 3 geological factors that caused the Tully Valley mudslide?
2. In what direction did the landslide flow?
3. In what direction does the Onondaga Creek flow?
4. Inferring from the map (which shows locations of mudslides), which side of the Tully Valley has the
steepest valley walls?
5. What is the force that drives a mudslide?
6. What are four factors or existing conditions that allow mudslides to occur?
Conclusions
7. Why do you think the 1993 Tully Valley Landslide occurred?
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