• Use photographs and topographic maps to identify mass wasting hazards
• Use particle size and shape to categorize mass wasting events
• Interpret evidence of mass wasting and categorize future risk of mass wasting
Laboratory Materials Needed
• Green colored pencil or marker
• Appendix E
Pre-Lab Assignment: Prior to the lab, read Chapter 15 Sections 15.1 and 15.2 in your textbook and read through this lab document.
Introduction
Mass wasting is the downslope movement of bedrock, rock debris or soil under the influence of gravity. While mass wasting events are commonly referred to as landslides, we will be learning about how we can more specifically identify mass wasting events in this lab exercise. In order to classify a mass wasting event, we need to know what type of material was involved in the event and how that material moved.
The first observation you will make is in the material type. We divide material into two main types: rock and unconsolidated materials. Rock refers to any solid, generally cohesive mass that moves as a single unit. Unconsolidated materials are those that move as loose particles independently of each other during the event. Table 1 summarizes the material types you will be using to identify mass wasting events in this lab exercise. In the next phase of your observations, you need to determine how the material moved during the event. The basic types of movements you need to understand are listed in Table 2.
Mass wasting events can happen anywhere and can involve more than one type of material or movement. For example, a material that began falling as a single cohesive mass from a high cliff might impact the base, break apart and begin moving as many small pieces. To help capture these unique changes and to provide you with a way to remember the different events, you will be using Figure 1 in Appendix E to classify the mass wasting events in the lab exercises.
Table 1: Material Classification
Material Composition
Consolidated Materials Rock Solid mass of bedrock that moves down slope as one solid piece
Unconsolidated Materials Debris Unconsolidated material ranging in size from large boulders to cobbles and sand-sized particles
Earth Unconsolidated sand-, silt- and clay-sized particles
Mud Unconsolidated silt- and clay-sized particles mixed with water
Table 2: Movement Classification
Type of Motion Description Evidence to Look For
Fall Occurs when a cohesive mass falls through the air from a steep to vertical incline or overhang. The material falls through free space at some point during the event. • Steep cliff faces or overhangs.
• Talus cones (piles of rock debris).
Slide Occurs when a cohesive mass or masses slide along a generally smooth inclined plane. • Inclined bedding planes, joints or fractures.
• Scarp surface at the upper boundary of the failure.
• Rock debris at the bottom.
Slump Occurs when a cohesive mass or masses rotate and slide along curving planes. • Distinct scarp at the top of the failure.
• Terraced or stepped appearance.
• Rock debris and even lobate “flow” at the base of the movement.
Flow Occurs when unconsolidated material moves downslope. Each particle moves independently during the event. • Round or lobate tongue of material at the base of the slope.
• Surface looks lumpy. No terracing. May or may not include vegetation.
Creep This is the movement of surface material slowly over time. It is cause by freeze-thaw or warm-cold cycles that lift the upper layer of sediment or soil. • Tilted fence posts, power lines, curved tree trunks
Exercise 1: Identifying Mass Wasting Events in photographs
Use the plates in Appendix E to complete the following questions. Remember to observe both the type of material and type of movement when forming your answers.- Figure 2: Canadian Rockies.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 2 using arrows and descriptions. Submit your marked Appendix with your completed lab.
- Figure 3: Chalet Du Fer Leysin, Switzerland.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 3 using arrows and descriptions. Submit your marked Appendix with your completed lab.
- Figure 4: The Black Hills, North Dakota.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 4 using arrows and descriptions. Submit your marked Appendix with your completed lab.
- Figure 5: Mission Pass, California.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 5 using arrows and descriptions. Submit your marked Appendix with your completed lab.
- Figure 6: Hayward Formation, Marathon, Texas.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 6 using arrows and descriptions. Submit your marked Appendix with your completed lab.
- Figure 7: Pacific Palisades, California.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 4 using arrows and descriptions. Submit your marked Appendix with your completed lab.
d. List three possible events that could have triggered the mass wasting event shown in Figure 7. Consider the topography, climate and geographic location when forming your answer.
- Figure 8: Alaska mass wasting event, March 1964.
a. How would you classify the material involved in the event shown in this location (Select one)?___________ Rock ___________ Debris ___________ Earth ___________ Mud
b. Using the chart in Figure 1, how would you classify this event?
c. What evidence did you use to determine this classification. Identify the evidence in Figure 8 using arrows and descriptions. Submit your marked Appendix with your completed lab.
d. Write a hypothesis that summarizes the series of events or conditions that might have triggered the mass wasting event shown in Figure 7. Consider the topography, climate, history and geographic location when forming your answer.
e. How could you test your hypothesis? Explain what evidence would you need to support your hypothesis.
Exercise 2: Investigating the Slumguilion Slide
In this exercise, you will use both photographs and topographic maps to investigate a classic mass wasting event.- Figure 9 is a photograph of the famous Slumguilion slide located in the San Juan Mountains in Colorado. Figure 10 is the topographic map of Lake Cristobal and the Slumguilion slide. The rocks in this area are primarily volcanic rocks dominated by andesite and pyroclastic material.
a. Trace the boundaries of the Slumguilion slide in green on the map in Figure 10.
b. Add an arrow pointing toward the source (head) of the slide on the map in Figure 10.
- What is the elevation of location A, which marks the contour that crosses the river south of Lake San Cristobal?
- What is the elevation of location B, which marks the contour that crosses the river north of Lake San Cristobal?
- Which direction does the river flow (select one)?
North to South South to North
- What is the elevation of the surface of Lake San Cristobal?
- What is the elevation of the point labeled Z on the map?
- Using the elevation of point Z and the elevation of the surface of Lake San Cristobal, how thick is the slide debris near the north shore of the lake? Show your calculation.
- What created Lake San Cristobal? Explain the likely process that lead to the formation of the lake.
- What areas might be considered a high risk for future slides? Shade or circle three high risk areas on the map in red. NOTE: Areas of high risk include lower gradient locations that are above steep slopes. Look for places where contours which are parallel suddenly diverge. One sample location has been identified in red as an example.