WEATHERING EROSION AND MASS WASTING c Vicki Drake

WEATHERING, EROSION AND MASS WASTING (c) Vicki Drake, 2010 1

What is Weathering? u u Weathering is the combined actions of all processes that cause rock to disintegrate physically or decompose chemically. Weathering processes include ‘physical’ weathering or ‘chemical’ weathering – Physical Weathering – breaks rocks down into smaller and smaller pieces – Chemical Weathering – completely alters minerals in rocks; creates new minerals (c) Vicki Drake, 2010 2

Weathering Factors u Factors that affect weathering include: – Mineralogy of parent rock – Mafic minerals least resistant to weathering – Felsic minerals more resistant to weathering – Climate u Humid climates = more chemical weathering u Dry climates = more physical (mechanical) weathering – Time u Longer the exposure time, the greater the weathering opportunity – Number of fissures or openings u More joints, cracks, and openings allow for greater weathering processes to occur – Degree of slope u Steeper slopes encourage greater weathering of exposed rocks (c) Vicki Drake, 2010 3

. Why and Where Does Weathering Occur? u Weathering occurs at the Earth’s surface as rock materials are exposed to the environment. u Weathering is possible because all rock materials – no matter how ‘solid’ - have openings (pore spaces) that allow air, water and other materials to do their work. (c) Vicki Drake, 2010 4

PHYSICAL (MECHANICAL) WEATHERING u Physical Weathering does not change the basic mineralogy of rock – rocks are disintegrated into smaller and smaller pieces, ready for transport u Key ingredient in physical weathering: water (c) Vicki Drake, 2010 5

TYPES OF PHYSICAL WEATHERING u Frost (Ice) Action: the role of water in weathering when it freezes – Frost shattering (ice wedging) – Frost heaving (ice heaving) u Stone polygons/rings in high latitude tundra u Pingos u u u Salt Crystal Growth Unloading and Exfoliation Bioturbation – Vegetation – Animal (c) Vicki Drake, 2010 6

FROST ACTION u Frost Action is the repeated growth and melting of ice crystals in pore spaces of soil and within rock fractures. (c) Vicki Drake, 2010 7

FROST SHATTERING/ICE WEDGING u This type of physical weathering occurs at high altitudes where there are definitive cycles of summer and winter. u Granites tend to be the most susceptible to this type of weathering – Most high altitude mountains are granitic (c) Vicki Drake, 2010 8

FROST SHATTERING/ICE WEDGING During a thaw cycle (summer, for instance), water from groundwater or precipitation finds its way into the fissures of rocks. u In winter, the water freezes and expands by up to 9% in volume pushing the fissure apart even further. u Over many freeze-thaw cycles, rock will break into smaller pieces. u (c) Vicki Drake, 2010 9

Frost Shattering/Ice Wedging (c) Vicki Drake, 2010 10

FROST SHATTERING/ICE WEDGING (c) Vicki Drake, 2010 11

FROST/ICE HEAVING u This type of physical weathering occurs in high latitude regions of the ‘arctic tundra’ u Tundra are the extremely high latitude vast open spaces, covered with low-growing grasses and sparse vegetation. – Some parts of tundra are more ‘bog-like’ – Underlain by permanently frozen soils at depth - permafrost – Only upper layers thaw during brief weeks of ‘summer’. 12 (c) Vicki Drake, 2010

MAP OF TUNDRA LOCATIONS (c) Vicki Drake, 2010 13

Tundra in summer Tundra in winter (c) Vicki Drake, 2010 14

PERMAFROST u Permafrost is permanently frozen soil, sediment, or rock. u Permafrost has a number of different layers, of which frozen ground is just one portion u The 'active layer' is ground that is seasonally frozen, typically lying above the perennially frozen permafrost layer. – This is the layer involved with ‘frost heaving’ (c) Vicki Drake, 2010 15

PERMAFROST The Active layer goes through repeated cycles of freezing and thawing Frost heaving occurs in the ‘active’ layer (c) Vicki Drake, 2010 16

HOW DOES ICE HEAVING WORK? u Summer thaw of upper ‘active’ layer allows water to migrate down through soil layers under gravity u Water ‘pools’ against the more permanently frozen soil layers u Winter freeze and water expands vertically, lifting up overlying soil layers (c) Vicki Drake, 2010 17

ICE/FROST HEAVING (c) Vicki Drake, 2010 18

RESULTS OF ICE HEAVING Roads can be affected by ice heaving by warping the surface As the water freezes, it expands vertically, pushing up the overlying layers (c) Vicki Drake, 2010 19

FROST HEAVING: PATTERNED GROUND AND STONE RINGS u Under the right conditions over hundreds of years, stone and soil organize themselves into patterns, through cycles of freezing and thawing. u The frost heaving activity found in the tundra can produce small hills with center depressions (up to 18 inches tall and 3 -4 feet across) (c) Vicki Drake, 2010 20

Patterned Ground: Stone Polygons (c) Vicki Drake, 2010 21

PINGOS u Pingos are ice-cored hills forming in the tundra In time, the expanding ice forms an isolated mass – its volume increases and it pushes up the overlying tundra u Pingos grow at a rate of approximately one-half inch per year u The tallest pingo in the world (in the western Arctic) is 16 stories (192 feet) high. u (c) Vicki Drake, 2010 22

PINGOS (c) Vicki Drake, 2010 23

PINGO IN NW ALASKA

Salt Crystal Action u u Similar to ice-crystal growth – salt crystals grow instead Susceptible rocks: – Sandstones in dry and arid regions u Process: – Groundwater moving down under gravity through permeable sandstone, naturally high in salts. – Water hits an impermeable layer (shale, for instance) – Water flows along impermeable shale to an opening – Water exits rock leaving salt crystals behind. – Salt crystals grow at base of cliff, producing niches (caves) – Base of cliff wears away, rest of cliff collapses and process begins again (c) Vicki Drake, 2010 25

WEATHERED SANDSTONE

Cliff Dwellers (c) Vicki Drake, 2010 27

UNLOADING AND EXFOLIATION Large sections of granitic rock, formed at great depth under pressure, brought to surface through plate tectonics. u At the molecular level, the granite expands in lower pressure environment u Develops fractures in form of thick shells that peel away from rock u Forms rounded features: domes, for instance u (c) Vicki Drake, 2010 28

EXFOLIATION (c) Vicki Drake, 2010 29

OTHER PHYSICAL WEATHERING u Surface Heating and Cooling – Expansion and contraction of rock over time – Fire fracturing u Bioturbation – Plant roots – Animal burrowing (c) Vicki Drake, 2010 30

BIOTURBATION Fire Roots Burrowing animals (c) Vicki Drake, 2010 31

CHEMICAL WEATHERING u Chemical weathering alters the minerals of rocks – in some cases, the minerals are dissolved. u Types of Chemical Weathering – Hydrolysis – Oxidation – Dissolution: Carbonic Acid Action (c) Vicki Drake, 2010 32

Hydrolysis u The addition of water at the molecular level to silicates. u Creates a grain-by-grain breakup of the minerals in Granite into a clay called Kaolinite – Kaolinite used in manufacturing of spark plugs and ceramic casings for lights. (c) Vicki Drake, 2010 33

Oxidation u The addition of oxygen molecules (a hydroxyl radical) to metallic minerals (such as iron) (think: RUST) u Results in decay of igneous and metamorphic rocks down to 100 meters or more in tropical areas (c) Vicki Drake, 2010 34

Dissolution: Carbonic Acid Action u The mixing of CO 2 and water creates carbonic acid – a weak acid u Carbonic acid attacks limestones and marbles: rocks composed of calcium carbonate (Ca. CO 3) u In regions underlain by limestone, removal of Ca. CO 3 results in development of karst topography (c) Vicki Drake, 2010 35

Karst Topography Regions with limestone bedrock being weathered out. u Results in landforms such as caverns, sinkholes, disappearing streams, and low elevation. u Karst is a German name for an unusual and distinct limestone terrain in Slovenia, called Kras. u (c) Vicki Drake, 2010 36

Karst Topography (c) Vicki Drake, 2010 37

EROSION AND MASS WASTING u Erosion: Movement of weathered rock over long distances by water or wind. u Mass Wasting: Downslope movement of weathered rock over short distances due to gravity (c) Vicki Drake, 2010 38

MASS WASTING u Main force moving weathered materials down slope is gravity. u Factors that control mass wasting: – Steepness of slope – Water content of materials – Presence (or absence) of native vegetation – Human activities (c) Vicki Drake, 2010 39

SLOPE STABILITY: STEEPNESS W = Weight of total mass of earth material (at center of mass). D = Vector component of W parallel to potential movement. N = Vector component of W normal to slip plane. (c) Vicki Drake, 2010 40

SLOPE STABILITY: WATER (c) Vicki Drake, 2010 41

SLOPE STABILITY: VEGETATION Native vegetation (such as chaparral) tend to grow on steep slopes. u Root structures act as binders and stabilizers of loose unconsolidated materials. u Removal of native vegetation through fire or clearing reduce stability of weathered materials on a slope. u (c) Vicki Drake, 2010 42

Vegetation’s role in slope stability: (A, B) Roots support and stabilize soils near surface and at depth C) Upslope soils stabilized by stems and roots close to surface

SLOPE STABILITY: HUMAN ACTIVITIES (c) Vicki Drake, 2010 44

SLOPE STABILITY: MIINING The Frank Slide: rock avalanche and is composed of limestone blocks mainly. At 4: 30 am on April 29, 1903, the face of Turtle Mountain, Alberta, Canada, collapsed onto the coal-mining town of Frank, killing at least 70 people. This landslide has a volume of 30 million cubic meters, and an equivalent weight of 90 million tons (c) Vicki Drake, 2010 45

TYPES OF MASS WASTING u u Rock fall – Talus slope development u Angle of Repose – Bedrock failure Slides – Material remains coherent and moves along defined surface: joint, fracture, bedding planes Slumps – Downward rotation of rock/regolith along concave -upward curved surface Flows – Materials flow down slope – mixture of water, rock and other materials (slow to fast movement) u Slurry: Lahar, Mud Flow, Debris Flow, Solifluction u Granular: Debris avalanche, Earth Flow, Soil Creep 46 (c) Vicki Drake, 2010 46

ROCK FALLS Fastest form of mass wasting Hundreds of tons of rock free-falling to surface (c) Vicki Drake, 2010 47

Granitic rock failure

TALUS SLOPES u u The pile of rocks that accumulates at the base of a cliff, chute, or slope. Movements occur whenever the talus slope exceeds the critical angle: “angle of repose” – ‘angle of repose’ is the steepest angle unconsolidated material may remain stable u u The exact angle at which failure takes place depends upon the materials, rock size, and moisture content Dry homogenous materials in a pile experience slope failure when the angle of repose (the resting slope angle) exceeds 33– 37° (c) Vicki Drake, 2010 49

TALUS SLOPES Talus (loose, weathered bedrock) falls to base of mountain building up a ramp that is very unstable (c) Vicki Drake, 2010 50

TALUS SLOPES AND EXFOLIATION

SLIDES: ROCK AND DEBRIS (c) Vicki Drake, 2010 52

PORTUGUESE BEND u Landslides have been active in this region of the Palos Verdes Peninsula for thousands of years beginning in the Holocene u The 1956 landslide has been attributed to human activities. – Human activities introduced ground water beneath the homes, lubricating a layer of bentonite clay formed by the subsurface weathering of volcanic rock called tuff. u Landslide encompassed an area of approximately 270 acres and involved over 160 homes. u Rates of slippage have varied, initially moving between 2 and 12 cm/day for the first two years, and diminishing to less than 1 cm/day during the next four years. u The slide mass has continued to move for over 40 years and the cumulative displacement exceeds 30 meters in some areas. (c) Vicki Drake, 2010 53

PORTUGUESE BEND, PALOS VERDES PENINSULA (c) Vicki Drake, 2010 54

POINT FERMIN LANDSLIDE u The Point Fermin landslide originally consisted of about 10. 5 acres that began sliding in 1929. u More movement in the early 1940’s was discovered when broken water pipes appeared. u Movement was slowed during the early 1960’s, however, damage to houses was enough to force evacuation of area (c) Vicki Drake, 2010 55

POINT FERMIN LANDSLIDE (c) Vicki Drake, 2010 56

SLUMPS (c) Vicki Drake, 2010 57

La Conchita, Ventura, CA (c) Vicki Drake, 2010 58

La Conchita Slide

FLOWS: LAHAR, DEBRIS, SOLIFLUCTION, AND EARTHFLOW u u Lahar: combination of volcanic ash, mud and water flowing down a stratovolcano during an eruption Debris Flow: combination of weathered rock, water and mud flowing out of canyons during extreme rain events – Alluvial Fans: formation of ramps along at mouths of canyons in arid areas u u Solifluction: slow down slope movement of upper layers of weathered tundra soils; form large lobes on slope Earthflow: downslope viscous flow of finegrained materials saturated with water under the influence of gravity (c) Vicki Drake, 2010 60

LAHAR (c) Vicki Drake, 2010 61

DEBRIS FLOW (c) Vicki Drake, 2010 62

CONTROLLING DEBRIS FLOW u Los Angeles County Flood Control developed two types of basins to attempt control of material flowing out of San Gabriel Mountains into foothill communities (c) Vicki Drake, 2010 63

DEBRIS and CATCHMENT BASINS (c) Vicki Drake, 2010 64

HOW DEBRIS BASINS WORK (c) Vicki Drake, 2010 65

WHEN DEBRIS BASINS FAIL Winter, 2010, La Cañada. Flintridge Debris Basin failure (c) Vicki Drake, 2010 66

SOLIFLUCTION

SOLIFLUCTION: TUNDRA SOILS (c) Vicki Drake, 2010 68

SOIL CREEP (c) Vicki Drake, 2010 69