Chapter 8
Download
1 / 74

Chapter 8 - PowerPoint PPT Presentation


  • 114 Views
  • Uploaded on

Chapter 8. Weathering, Soils and Mass Movement BFRB Pages 157 - 161. Weathering and Erosion. Weathering - Def . - the break down of rocks that have been exposed to the atmosphere.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Chapter 8' - trygg


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Chapter 8

Chapter 8

Weathering, Soils and

Mass Movement

BFRB Pages 157 - 161


Weathering and erosion
Weathering and Erosion

  • Weathering - Def. - the break down of rocks that have been exposed to the atmosphere.

  • Once the rocks are broken down, the pieces are transported from one place to another. This process is callederosion.

  • Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity.

  • VIF - Most erosion that takes place on Earth is caused by moving water


What is w e d
What is W.E.D.?

  • Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes.

  • Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is calledErosion.

  • Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.



2 types of weathering

Chemical weathering Dandy” ESRT’s…– rocks break down as their minerals change in chemical composition (they become different substances).

Physical weathering– rocks are broken down into smaller pieces without changing their chemical composition (what they’re made of).

AKA - mechanical weathering

2 Types of Weathering


Agents of physical weathering

Agents of Physical Weathering Dandy” ESRT’s…


Types of physical weathering
Types of Physical Weathering Dandy” ESRT’s…

  • #1 - Frost action (aka Ice Wedging)

    • water enters small cracks in the rock.

    • when water freezes, it expands and forces the crack to open more.

    • the ice melts back into liquid water and fills the crack again.

    • the process repeats over and over again until the rock breaks apart.





Types of physical weathering1
Types of Physical Weathering Dandy” ESRT’s…

  • #2 - Abrasion

    • It is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in windy areas, under glaciers, or in stream channels.

    • It can also happen during rock slides (gravity)


Rocks that have undergone different kinds of abrasion look very differently
Rocks that have undergone different kinds of abrasion look very differently!

Rock weathered by a rockfall

Rock weathered by a stream


Types of physical weathering2
Types of Physical Weathering very differently!

  • #3 Plant RootsThe roots of trees often wedge in between cracks in rocks and force apart rocks even further as they grow!


Types of physical weathering3
Types of Physical Weathering very differently!

  • #4 Animals Animals (worms, groundhogs, rabbits, etc.) burrow into the ground exposing more rock surfaces to the agents of weathering.


Types of physical weathering4
Types of Physical Weathering very differently!

  • #5 Wetting and drying

    • Breaks up rocks that are made from clay.

    • When they are wet they expand, and they shrink as they dry.

    • As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!


Types of physical weathering5
Types of Physical Weathering very differently!

  • # 6 - Exfoliation

    • soil and rock is removed (glaciers or uplifting), exposing rock found deep underground.

    • This releases the pressure causing the surface of the rock to expand and eventually crack and flake off.


Horizontal Exfoliation very differently!


Horizontal Exfoliation very differently!


Vertical Exfoliation very differently!



Agents of chemical weathering1
Agents of Chemical Weathering very differently!

  • #1 - Hydrolysis

    • water (hydro) reacts with minerals such as feldspar and hornblende to form clay which weakens the rock and breaks it apart..

Link to visualization


Agents of chemical weathering2
Agents of Chemical Weathering very differently!

  • #2 - Plant Acids - Lichen & Moss

    • These plants live and grow on rocks and eventually break them apart by the weak acids that they secrete!

Lichen – light green/looks like bread mold

Moss – dark green


Agents of chemical weathering3
Agents of Chemical Weathering very differently!

  • #3 - Oxidation

    • oxygen reacts with some minerals, especially those containing iron to form rust (called iron oxide).

    • The rusty spots weaken the rock and it breaks apart.

    • Water is not needed for oxidation to occur, but it does speed up the process!


Chemical weathering of basalt - an iron rich (mafic) igneous rock!

You see, it all comes together!!!


Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)


Agents of chemical weathering4
Agents of Chemical Weathering white/yellow, weathered deposits are reddish-brown)

  • #4 - Acids in water

    • Carbon dioxide, nitrogen dioxide, and sulfur dioxide dissolve in water and create carbonic acid, nitric acid, and sulfuric acid.

    • This acidic water can cause rocks to dissolve, especially those containing calcite like limestone and marble!

    • Acids may be found in ground water (forms caves) or in rain water (acid rain).



Pitted limestone from rainfall weathered by acid rain


Carbonic acid weathered by acid rain in groundwater causes caves to form.

When the acidic groundwater comes in contact with limestone, the limestone dissolves and caves and caverns are formed.

Howe Caverns in NY and Carlsbad Caverns in NM are examples of these beautiful geologic formations


Stalactites weathered by acid rain

Stalagmites

Carlsbad Caverns – New Mexico


Rates of weathering

Rates of Weathering weathered by acid rain


Factors that affect rates of weathering
Factors that affect rates of weathering: weathered by acid rain

  • Rock’s resistance to weathering (HARDNESS)

  • Amount of surface area

  • Climate:

    • Chemical weathering occurs faster in warm, wet climates

    • Mechanical weathering occurs faster in cold or dry climates


The central area of rock was weathered by acid rainless resistant to weathering…thus the “arch” was formed! This is differential weathering.


Devil’s Tower, Wyoming - An igneous intrusion (volcanic neck – the underneath of the volcano) surrounded by less resistant sedimentary rock layers. Erosion has exposed this monolith! This is an example of differential weathering!!!

You may recognize it if you’ve ever seen “Close Encounters of the Third Kind”


Surface area
Surface Area neck – the underneath of the volcano) surrounded by

  • Greater surface area increases the rate of weathering

  • Surface area is the amount of rock surfaces exposed to the atmosphere

  • Weathering creates more surface area


Dry climate mechanical weathering
Dry Climate = Mechanical Weathering! neck – the underneath of the volcano) surrounded by

Devil’s Marbles, Australia – Mechanical weathering from wind and sand!


Wet climate chemical weathering water speeds up chemical reactions
Wet Climate = Chemical Weathering! neck – the underneath of the volcano) surrounded by (water speeds up chemical reactions)

Water runoff seeps into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away granite minerals such as feldspar and mica!


Alternating cold warm climate mechanical weathering via frost action
Alternating Cold & Warm Climate = Mechanical Weathering neck – the underneath of the volcano) surrounded by (via frost action)


Warm moist climate chemical weathering heat moisture speed up chemical reactions
Warm & Moist Climate = Chemical Weathering neck – the underneath of the volcano) surrounded by (heat & moisture speed up chemical reactions)

Parthenon – Athens, Greece


Dry climate mechanical weathering via wind blown sediment
Dry Climate = Mechanical Weathering neck – the underneath of the volcano) surrounded by (via wind blown sediment)


Soil formation

Soil neck – the underneath of the volcano) surrounded by Formation


What is soil made of
What is soil made of? neck – the underneath of the volcano) surrounded by

Soil has 4 components:

  • Weathered rock

  • Organic material (humus)

  • Air

  • Water


There are 2 types of soil
There are 2 types of soil…. neck – the underneath of the volcano) surrounded by

PARENT MATERIAL is the rock that the soil forms from

  • When the parent material is the underlying bedrock of the area, the soil is called RESIDUAL SOIL (residual = what is left behind when the bedrock weathers – it still “resides” or lives with the parent material)

  • If the soil was formed in one place and carried (transported) elsewhere (by wind, water, glaciers, etc…) then the soil is called TRANSPORTED SOIL

    VIF - MUCH OF THE SOIL IN NYS IS TRANSPORTED SOIL LEFT BEHIND BY GLACIERS!


Cross section of soil layers neck – the underneath of the volcano) surrounded by

Each layer is called a HORIZON

Horizon O/A = Topsoil (mostly humus, some weathered rock)

Horizon B = Mostly weathered rock, some organic material (mineral rich zone)

Horizon C = Broken Bedrock

BEDROCK


HORIZON A neck – the underneath of the volcano) surrounded by

HORIZON B

HORIZON C


Mass movements

MASS MOVEMENTS neck – the underneath of the volcano) surrounded by

MOVEMENTS OF SOIL, ROCK, AND LOOSE MATERIALS CAUSED BY THE FORCE OF GRAVITY


Creep slow mass movement
CREEP neck – the underneath of the volcano) surrounded by (Slow Mass Movement)

  • Very slow downward movement of soil

    • Only noticeable by the results of trees, fence posts, telephone poles, etc… that are tilted downhill


Landslide rapid mass movement
LANDSLIDE neck – the underneath of the volcano) surrounded by (Rapid Mass Movement)

  • Sudden movement of soil downhill (usually a very steep slope)

    • AVALANCHE – landslide made of Ice & Snow as well as Soil

    • SLUMP – small areas of land moving downhill - especially along roadways that cut into the side of hills


Mudflow or lahar rapid mass movement
MUDFLOW neck – the underneath of the volcano) surrounded by or LAHAR(Rapid Mass Movement)

  • Very fast & dangerous movement of water saturated soil (MUD)


Even though rapid mass movement is more noticeable than slow mass movement, overall, more material is transported via creep than all others combined – because it is occurring in many more places and all the time!!!!


ad