GEOL 102: Earth and Environment 2024 Fall Lecture Notes PDF

GEOL 102: Earth and Environment 2024 Term 3 (Fall) GEOL 102, URegina Prof J. McBeth Copyright 2024, Dr Joyce McBeth, University of Regina Image Source: NASA, Public Domain 2024-11-19 Announcements Lab this week – please go! Very tricky to...

GEOL 102: Earth and Environment 2024 Term 3 (Fall) GEOL 102, URegina Prof J. McBeth Copyright 2024, Dr Joyce McBeth, University of Regina Image Source: NASA, Public Domain 2024-11-19 Announcements Lab this week – please go! Very tricky to reschedule at this point due to various factors so less options to make up labs. Midterm #2 results – I am waiting to receive the scantron marking results, will update on Urcourses page when they arrive. Office hours this week: Th/Fri 2-4:30 pm. Come review your midterm #1 (and #2 if I have the results back), and/or discuss study strategies for the final. Image: slope failure along the Kiskatinaw River in northeastern BC. Source: Joyce McBeth (2018) CC BY 4.0 URegina Mass Wasting 2024 Fall GEOL 102 J. McBeth Suggested Readings From Physical Geology 1st USask Edition (Panchuk) Chapter 15: 15.1 Factors That Control Slope Stability 15.2 Classification of Mass Wasting 15.3 Preventing, Delaying, Monitoring, and Mitigating Mass Wasting Textbook and Workbook sections: Mass Wasting Textbook Chapter 15: https://openpress.usask.ca/physic algeology/part/chapter-15-mass- wasting/ Workbook Chapter 15: https://openpress.usask.ca/geolw orkbook/part/chapter-15-mass- wasting/ Learning Outcomes Describe the differences between weathering, erosion, and mass wasting. Describe the factors that drive mass wasting and how variations in these factors can influence slope stability. Give examples of natural and anthropogenic causes of mass wasting. Describe the three factors used to classify mass wasting events. Draw and describe the different kinds of mass wasting events. Describe which regions of Canada have the most mass wasting events and why. Describe some of the measures we can take to prevent or lessen the mass wasting events. Weathering, Erosion, and Mass Wasting Weathering: Chemical and physical processes that produce soils, clays, sediments, and dissolved substances - a key process in the rock cycle Erosion: Removal and transport of particles produced by weathering from their source by wind, water, and ice Mass wasting: Movement of Earth materials down a slope due to gravitational force Mass Movements Downslope movement of Earth materials under the force of gravity Includes soils, rock, sediments, mud. Occurs when the force of gravity exceed the strength of slope materials Different than erosion by wind, water, or ice http://www.cbc.ca/news/canada/british- columbia/story/2012/07/12/bc-landslide-johnsons- landing.html Building on a slope – where is it a bad idea? What do we need to consider before doing it? Road cut in the Himalayas Source: https://www.hindustantimes.com/ Mass Wasting Influenced by three primary factors: 1. Material characteristics: slopes may be composed of unconsolidated (regolith) or consolidated materials 2. Water content: affected by precipitation and material porosity 3. Slope steepness: influences how materials move under various conditions Slope steepness and water content are the factors most strongly influenced by human activity Examples: road cuts Material characteristics: Consolidated materials are stronger than unconsolidated materials Angle of repose (maximum angle of unconsolidated materials) is greater for courser and less rounded materials Slope Materials Unconsolidated sand and silt Ultimately form slopes with a maximum angle (angle of repose) of ~35° Steeper slopes will collapse to angle of repose Unconsolidated mixtures Combinations of sand, silt, clay, soil, and rock fragments (debris) can form moderate to steep slopes Consolidated materials Rock, lithified sediments, vegetated soils, and cohesive particles often form more stable slopes Water Content Affects the stability of both consolidated and unconsolidated materials Mass movements of consolidated materials are usually linked to increasing water content https://twitter.com/mu_earthscience/status/1025048202746183680 Water Content Saturated materials lose strength because water reduces frictional forces between particles Liquefaction occurs if water content increases enough to allow materials to flow as a fluid Source: Steven Earle (2015) CC BY 4.0 Water content and unconsolidated sediment cohesion Surface tension: http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html Slope steepness and slope stability Stability of slopes depends upon: physical characteristics of soil, rock, and other slope materials (including water) Component of gravitational force parallel to slope (shear force) increases with slope steepness If shear force exceeds shear strength, slopes can fail Source: Steven Earle (2015) CC BY 4.0 What are some causes for mass wasting events? Source: https://www.bbc.com/news/science-environment-18872398 Causes of Mass Wasting A combination of material properties, moisture, and slope steepness control the potential for slope material movement Natural processes that can cause mass wasting: Earthquakes Rainfall Chemical/mineralogical changes Frost wedging/thawing Human activities that can cause mass wasting: Adding weight Slope steepening Increasing moisture Removing vegetation Slope Steepening Cecil Lake road landslide, Beatton River, BC (Photo by R. Couture, GSC) Deforestation Taraza, Antioquia, Colombia Irrigated lawns golf course in Portugal Source: https://www.valedolobo.com Thawing Permafrost Lake near Ft. MacPherson, NWT Classification of Mass Movements Three characteristics used to classify mass movements: 1. Type of material that fails E.g., rock or unconsolidated material 2. Rate of movement How fast the material moved 3. Mechanism of failure Fall, slide, or flow Not all mass movements are landslides; however, the term landslides is often broadly used to describe mass movement events.  Creep Gradual downslope movement of soil or regolith Rates depend upon soil type, vegetation, climate, slope steepness, vegetation Creep Example: East riverbank of the South Saskatchewan River, Saskatoon Photographs by: Richard Marjan, The StarPhoenix  Terraced structures formed by soil creep Terracettes Commonly produced by creep combined with freeze-thaw cycles, or cycles of soil saturation and drying Source: Wikimedia user “Derek Harper” (2009) CC BY-SA 2.0 Solifluction Freeze-thaw activity generated mass movement Thawed water saturated soil flows over frozen layer underneath Generally form lobes and sheets on slopes Source: https://deskgram.net/p/1955353886373976930_2240716913 Useful vocab to describe rupture surface shape Curved: rotational slope failure, e.g. slump Flat: translational slope failure, e.g. rock slide Translate: move from one place to another directly, in a straight line Slump – a type of rotational slope failure Rock slide – a type of translational slope failure  Concave and cliff-like scarp (steep slope) Slumping Block moves coherently (as one unit) along the failure plane Often form stair step pattern of displaced blocks – secondary slumps Hummocky ridges near the toe of the slump Frequently form due to erosion or undercutting at base of slope Rotational slope failure Unconsolidated sediments Steven Earle on a steep slope near to Lethbridge, AB, 2005 Rock Slide An example of a translational slope failure 1903 rock slide, Frank, BC Rock Fall 2008 rock fall, Sea-to-Sky Highway, BC Photo by: Rob Kruyt / REUTERS  Type of material: rock Rock fall Rate of movement: fast Mechanism: fall Hunstanton, Norfolk, UK. Source: Joyce McBeth (2017) CC BY 4.0 Mud Flow Picture: AP Photo/Ted S. Warren 2014 landslide, Oso WA, USA Oso, Washington (USA) Mud Flow Occurred March 22, 2014 at 10:37 am 43 fatalities Collapse of 240 m of structurally weak sand and gravel terrace deposited during last period of glaciation Likely triggered by soil saturation resulting from heavy rainfall >200% normal rainfall in 45 days prior to landslide Extensive series of landslides in valley Last major slide occurred in 2006 https://www.facebook.com/USGeologicalSurvey Summary table of some common types of mass wasting Failure Type Type of Material Type of Motion Rate of Motion Vertical or near-vertical fall (plus Rock fall Rock fragments Very fast (>10s m/s) bouncing in many cases) Motion as a unit along a planar surface Typically very slow (mm/y to cm/y), Rock slide A large rock body (translational sliding) but some can be faster Flow (at high speeds, the mass of rock Rock A large rock body that slides and then fragments is suspended on a cushion of Very fast (>10s m/s) avalanche breaks into small fragments air) Creep or Soil or other overburden; in some Flow (although sliding motion may also Very slow (mm/y to cm/y) solifluction cases, mixed with ice occur) Thick deposits (m to 10s of m) of Motion as a unit along a curved surface Slump Slow (cm/y to m/y) unconsolidated sediment (rotational sliding) Loose sediment with a significant Flow (a mixture of sediment and water Mudflow Moderate to fast (cm/s to m/s) component of silt and clay moves down a channel) Flow (similar to a mudflow, but typically Debris flow Sand, gravel, and larger fragments Fast (m/s) faster) Source: Steven Earle (2015) CC BY 4.0 Translational or rotational slope failure? What kind? Source: J. McBeth (2017) CC-BY 4.0 Landslides in Canada Fatalities Most regions are 3 - 10 susceptible, but 10 - 50 some more than >50 others Most fatalities have occurred in B.C., Quebec, and Newfoundland Source: Atlas of Canada Landslides in Canada Why are some areas particularly prone to mass wasting? steep, mountainous terrain high precipitation (rain and snow) abundance of unconsolidated glacial sediments geographic position (e.g. earthquake zone) Several factors combined increase landslide risk Source: Atlas of Canada