GEOSC 10: Geology of the National Parks Tearing Down Mountains I: Weathering, Mass Movement, & Landslides Presented by Dr. Sridhar Anandakrishnan The Pennsylvania

GEOSC 10: Geology of the National Parks

Tearing Down Mountains I:Weathering, Mass Movement, & Landslides

Presented by Dr. Sridhar AnandakrishnanThe Pennsylvania State University

GEOSC 10 - Geology of the National Parks

Erosion

•Erosion

‣ Weathering

‣ Transportation

‣ Deposition on the Earth’s surface

•Landscapes created and destroyed

• Involves atmosphere, water, gravity


Erosion Agents

•Agents:

‣ Mass wasting

‣ Running water (streams)

‣ Glaciers

‣ Wind

‣ Ocean waves

‣ Ground water


Outline

•Mass wasting

‣ Tetons National Park

•Soils

‣ Badlands National Park

•Rain

‣ Redwoods National Park


Selected National Parks

Badlands

Redwoods

Tetons


Mass Wasting

•Masses of debris or bedrock moving downhill

•Landslides and slower movements

•Driven by gravity



Classification of Mass Wasting

•Rate of movement

‣ Soil creep to slumps to mudflows

•Extremely slow (~1mm/year) to very rapid

(>100 km/hour)

‣ Soil creep is slowest but ultimately most important - it happens everywhere

‣ Others happen in wet and/or steep places



Controlling Factors

•Most important: Water

•Climatic controls

‣ Ice

‣ Vegetation


Controlling Factors

•Water adds weight

‣ BUT a little water makes soil stronger (damp sand castle)

- “the water holds the grains together”

‣ Too much water makes soil weak

- “floats the grains apart”

•Vegetation

‣ Absorbs excess water from soil (increasing strength)

‣ Binds soil together (increasing strength)


Controlling Factors

•Overgrazing

‣ Reduces vegetation

- Weakens soil

- Allows water to enter soil

•Overloading

‣ Dumping of mine debris

‣ Heavy buildings on steep, denuded hillsides









Mudflow

‣ Flow of watery debris

‣ Occurs where lack of vegetation:

- Dry climates

- Volcanoes

- After forest fires

‣ Very fast up to 80 km/hr

‣ Triggered by heavy rainfall

‣ Los Angeles


Most Common Mass Wasting

•Soil creep

‣ gentle slopes

‣ vegetation slows movement

‣ very slow flow (< 1 cm/year)

- facilitated by water in soil

- by freeze-thaw in colder climates

‣ Freezing of water expands soil. Thawing drops the grains downhill.

Freeze

Thaw





Outline

•Mass wasting

‣ Tetons National Park

•Soils

‣ Badlands National Park

•Rain

‣ Redwoods National Park


Selected National Parks

Badlands

Redwoods

Tetons


Weathering

•Breakdown of rocks at the Earth’s surface

•Factors controlling weathering

‣ Presence of water

– Gasses

‣ Changing temperatures

‣ Biological organisms

– Pressure changes


Definitions

•Parent material is removed by erosion

•Transport by wind, water, glaciers

• In-place weathering produces soil

•Differential weathering for different rock types


Mechanical Disintegration

•Physically break rocks into smaller pieces

•Frost wedging and heaving

•Pressure release

•Thermal expansion

•Biological organisms

•Salt Crystal growth


Frost Action

•Water expands when it freezes

•Necessary conditions

‣ Temps that go below freezing

‣ Free water

‣ Cracks for the water to seep into

•Rocks spall off and form a talus slope



Figure 5.4,

p. 113


Pressure Release

•Rocks that form under high pressure

‣ Deep in the earth

‣ Subsequent uplift to the surface




Thermal Contraction/Expansion

•Rocks expand when heated and shrink when cooled

• Interior remains at a steady temperature

•Resulting in fracturing

• Important during fires

•On the Moon


Biological Organisms

•Tree roots and trunks

•Burrowing insects, worms, animals

•Earthworms

•Help to expose deeper layers to water

•Mix soils and circulate them to the surface



Chemical Weathering

•Rainwater with carbon dioxide (CO2)

‣ Forms a weak acid

•Acid attacks the rock

‣ Results depend on what type of rock

‣ Temperature, acidity, water, etc.


Granite and Acids

•Granite in the presence of carbonic acid will weather and break apart

•The Iron (Fe) will rust (oxidize)

‣ It usually remains in the soil

•The Aluminum (Al), Potassium (K), and Silica (SiO2) turn into clays and remain in the soil


Some of the Products Wash Away

•The Calcium (Ca), sodium (Na), and Magnesium (Mg) wash away

‣ The Ca goes into the sea and is used by sea creatures to make their shells

‣ The Na makes the sea salty

‣ The Mg reacts with rocks at the spreading centers to make new rocks


Soil

•What is left behind is soil

•More heat, more water --> more stuff is washed away and the soil has fewer minerals in it.

•Very dry areas, the Ca, Mg, and even Na remain and the soil is very salty


Badlands

•Erosion from the Rockies, deposited in the great plains.

•Soil is very clay rich

‣ The clays create a hard surface that channels the water, washes away plants

‣ The clays are unstable, slopes slump down, washing away plants

‣ Water doesn’t soak in well.


Wind and Weather


Wind and Weather

•Hot @ equator, cold @ N/S Pole

‣ Because the sun shines straight down @ equator

‣ Curve of earth makes sunlight spread out @ Poles

•Hot air rises @ equator, forms convection cell

‣ Cools off in upper atmosphere, is shoved N/S

‣ Comes down in the mid-latitudes

‣ Returns to Equator



World’s Deserts

Image courtesy USGS


Rain Shadow Desert

•Death Valley dry and hot because it is in the rain shadow of the Sierras.

•Warm, wet air rises from the CA coast and cools.

‣ Cool air holds less water, so it rains.

‣ Water vapor to rain releases heat

- opposite of the way evaporation of sweat takes in heat...


Rain Shadow Desert (2)

•So, the air that gets to the top of theSierras is dry and “warm”

‣ It only cools by 0.6C/100m because of the rainfall

‣ If it had been dry to begin with, it would have cooled by 1C/100m.

•When that dry, “warm” air goes down the other side it warms by 1C/100m

•Death Valley is HOT AND DRY


Documents

GEOSC 10: Geology of the National Parks Tearing Down Mountains I: Weathering, Mass Movement, & Landslides Presented by Dr. Sridhar Anandakrishnan The Pennsylvania