Mass Wasting Erosion Soils Weathering

Weathering: Regolith: Soil: the upper-most layer of the physical and chemical breakdown of rock – exposed to wind, water, ice, and living organisms Regolith: loose or broken rock layers resulting from weathering Regolith covers most of the earth. Soil: the upper-most layer of regolith that supports life

Do “things” last for ever ? Consider : new concrete a 1955 Chevrolet

Rocks can be broken down or chemically altered on the earth’s surface. Mechanical Weathering: Rocks are physically broken down by various surface processes into smaller parts without changing physical properties. Chemical Weathering: Rocks are altered from one form to a completely new form with a different set of physical properties.

I weathering Discuss with a friend: Describe the difference between mechanical and chemical weathering. 2. Give two examples of MW and CW you have observed. I will get an A on my exams and quizzes

Rock Mechanical Weathering – the breaking down of rocks How do we expose “more surface” area for chemical weathering to do its job ? Let’s show some surface Rock More surface area Less surface area Increased mechanical weathering accelerates chemical weathering.

Types of Mechanical Weathering Processes Frost Wedging: repeated cycles of freezing and thawing Water Water Freezes (expands) pieces break off (watch for falling rock) rock rock Dominantly takes place in freezing / thawing areas Unloading – reduction of pressure from overlying rocks -- take the pressure off me. overlying rocks Sheet like structures granite pluton Sheet like structures eroded and uplifted granite pluton

Frost Wedging – rocks are broken into plates and split apart.

Exfoliation Dome – granite is “sheeting” from loss of pressure due to unloading processes.

Types of Mechanical Weathering Processes Biological Activity – breaking down rocks through animal burrowing humans plant roots Human intervention Animal burrowing Plant root weathering

I mechanical weathering Discuss with a friend: Why is MW important? 2. Briefly describe how frost wedging, unloading and biological activity contributes to mechanical weathering I will get an A on my exams and quizzes

Chemical Weathering Rocks are chemically altered producing a new compound Why would a perfectly good rock want to change it’s appearance? STABILITY! Rocks require stability and achieve equilibrium with it’s surroundings Most rocks are not chemically stable at the earth’s surface Minerals (compositions) change to become stable at surface conditions

What common agent can begin the process of chemical alteration????? The Universal Solvent – WATER (H2O) How would we speed up the action of water? Rain + ????? What in the atmosphere is added to water to create a weak acid? H2O (rain) + CO2 (atmosphere) = H2CO3 (carbonic Acid) Let’s weather some granite with the natural acid H2CO3 Granite – the most abundant continental rock weathering the potassium feldspar (orthoclase) bicarbonate potassium silica orthoclase carbonic acid water kaolinite clay 2KAlSi2O8 + 2(H+ + HCO3) + H2O Al2Si2O5(OH)4 + 2K + 2HCO3 + 4SiO2 Granite has been chemically weathered and broken down into individual grains. in solution

Reduced to Clay

I Chemical weathering Discuss with a friend: What is the universal solvent? 2. How is carbonic acid naturally Produced? 3. How would you describe the “last” or most reduced material ----- the end product of chemical weathering? I will get an A on my exams and quizzes.

Soil – product of weathering containing solids, liquids, and gas. CLAY What’s in your soil? Loam – dominant soil fraction Humus – partially decayed organic material CO2/Air – fills the soil voids Water – wets the soil and carries high levels of dissolved substances SAND SILT

Soil Profiles: O A E B C horizons: a layer of soil with distinctive physical and chemical properties. sequence of soil horizons from the surface to the underlying bedrock O A O- Organic matter (humus) E A- Dark layer mixed with mineral and organic matter B E- light colored layer produced from removal of soluble material “leaching” C B- accumulation of clay C- weathered parent rock

Factors that influence soil formation: Parent Material: residual regolith – soil forms emplace or “insitu” Soil forms and weathers emplace from parent material. transported regolith – regolith that is moved by rivers, wind, and ice transported river deposits transported regolith on Mars

Factors that influence soil formation: Climate – soil profiles differ around the world which is directly influenced by climate arid soils vs. tropical soils Living organisms – a HUGE influence on soils Plants make organic matter. (humus) – animals mix the soil and recycle air and water. Topography – the contour or “slope” of the land Time – the longer the time the more mature a a soil becomes --- 1000’s of years

Mass Wasting

Mass Wasting What do these pictures have common?

GRAVITY What is Mass Wasting ? down-slope movement of rock and soil under the direct influence of GRAVITY What force acts alone – to create movements of the earth? GRAVITY

The role of Mass wasting– What’s it good for? Responsible for the evolution of landforms – features of the earth weathering weakens rock – does not create significant landforms need mass wasting to impact weathering and shape significant earth features River Valley widened by mass wasting Example: River Valley from weathering

I mass wasting Discuss with a friend: 1. What is mass wasting ? 2. What single “force” acts alone to produce mass wasting processes? 3. What is the sole purpose of mass wasting? I will get an A on my exams and quizzes.

So, what “triggers” a mass wasting episode allowing gravity to move the mass downward? The role of water Slopes to steep removal of vegetation Earthquakes

The Role of Water Water saturates surface materials. Particles loose their cohesion (can’t stick together). Particles slide past one another and slip downward under gravity forces.

steeper slopes exceed the “angle of Slopes to Steep steeper slopes exceed the “angle of repose” and material moves downward to stabilize or reach equilibrium. Angle of repose: the angle at which particles are overtaken by gravity and move downward angle depends on size, shape, and moisture content of accumulated particles Wet Sand Dry Sand

Removal of Vegetation where plants are lacking – mass wasting attacking root systems bind soil where soil is removed frequent down slope movements occur

The Role of Earthquakes Areas that have not moved in “years”, are activated by seismic waves. Mass slide produced by an earthquake dammed a river forming a lake.

I Mass Wasting Discuss with a friend: Describe the 4 triggers that enable mass wasting process. 2. What the angle of repose? 3. What is the most dominant “trigger” causing the onset of mass wasting? I will get an A on my exams and quizzes

How do geologists classify various mass wasting processes? Classification is based on Unconsolidated: debris, mud, earth Material Bedrock: rock Fall: freefall of material Slide: material moves cohesively along well defined surface Flow: material moves down-slope as a viscous fluid Motion

I Mass Wasting. Discuss with a friend: What two criteria do geologist use to classify mass wasting movements? I will get an A on my exams and quizzes

Mass Wasting Processes Classification of Mass Wasting Processes

SLUMP downward movement of a sliding mass, rock or unconsolidated material that moves as a single unit along a curved surface moves very slow over-steepened slopes (T) water saturated (T)

Rockslide Debris slide blocks of bedrock break loose and slide down a slope Over steepness (T) Debris slide unconsolidated material break loose and slide down a slope Debris flow Rockslide

Debris Flow rapid mass movement containing soil and regolith with large amounts of water Water saturation (T)

Lahars debris flows composed largely of volcanic material from the flanks flows down existing stream valleys extremely destructive events’ water saturation (T) Lahars buried a village

Earth Flow form on hillsides in humid areas with abundant precipitation water saturated – hill may break away under gravity and weight of soil water saturated (T) rich in clays and silt slow moving flows

Soil Creep the gradual downhill movement of soil and regolith. soil moves extremely slow soil disturbed by rain, roots water saturation (T)