Transcript GLG101online_07A_WeatheringandSediment_MCC_Leighty

Weathering, Erosion,
and Sediment
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Weathering
& Sediment
Weathering
 Mechanical - Rocks disintegrate (break)
 Chemical - Rocks decompose (rot)
 Erosion (weathering) – physical removal of material by water,
wind, and/or ice
Weathering
& Sediment
Mechanical Weathering
 Rocks break into small pieces that still have the same composition
as the parent material
 Increases the surface area
parent
material
Weathering
& Sediment
Mechanical Weathering
Frost Action
 Freeze/thaw cycle (water expands by 9% upon freezing)
joints
Weathering
& Sediment
Mechanical Weathering
Frost Action
talus (scree) slope
Weathering
& Sediment
Mechanical Weathering
Thermal Expansion/Contraction
 Rock expands (higher T's) and shrinks (lower T's)
Weathering
& Sediment
Mechanical Weathering
Exfoliation (pressure release)
rock expands when uplifted
to the surface
(lower confining P)
it cracks & forms
sheet joints
Weathering
& Sediment
Mechanical Weathering
Exfoliation (pressure release)
sheet joints in Yosemite N.P.
Weathering
& Sediment
Mechanical Weathering
Exfoliation (pressure release)
 Spheroidal weathering - exfoliation on a smaller scale
Weathering
& Sediment
Chemical Weathering
 Parent rock material is decomposed by chemical alteration into
new materials
Weathering
& Sediment
Chemical Weathering
Dissolution
 Some rocks & minerals dissolve in acidic solutions
ex: feldspar dissolves in carbonic acid
Weathering
& Sediment
Chemical Weathering
Dissolution
ex: calcite dissolves in HCl acid
Weathering
& Sediment
Chemical Weathering
Hydrolysis
 Minerals converted into clay (Al + Si + O)
ex: feldspar (mineral) + acid + water  clay (residue) + water (with dissolved Si, Na, Ca, K)
Weathering
& Sediment
Chemical Weathering
Hydrolysis
ex: brewing coffee
Weathering
& Sediment
Chemical Weathering
Oxidation
 Minerals react with oxygen to form oxides
ex: iron oxidizes to hematite (reddish rocks)
Weathering
& Sediment
Chemical Weathering
Weathering
& Sediment
What is sediment?
 Sediment = loose solid particles derived from the weathering of
preexisting rocks
Weathering
& Sediment
Describing Sediment
Size
 Clast size – how big are the pieces (clasts)?
> Sediments are classified according to size
2 mm
gravel
1/16 mm
sand
silt
clay
mud
Weathering
& Sediment
Describing Sediment
Rounding
 Clast rounding – how rounded are the edges?
angular
rounded
Weathering
& Sediment
Describing Sediment
Sorting
 Clast sorting – what is the range of grain sizes?
different sizes
similar sizes
Weathering
& Sediment
Sediment Transportation
 Abrasion reduces the size of clasts & rounds the edges with
distance
Weathering
& Sediment
Interpreting Sediment
 Size, rounding, and sorting of clasts tell us about:
a) Distance of transport from source area
> Smaller, more rounded, & well-sorted clasts
= more abrasion = longer transport distances
b) Current energy
> Larger pieces = high-energy current (beach, stream, etc.)
> Smaller pieces = low-energy deposition (lake, flood plain,etc.)
Weathering
& Sediment
WWW Links in this Lecture
> Weathering - http://en.wikipedia.org/wiki/Weathering
> Erosion - http://en.wikipedia.org/wiki/Erosion
> Physical weathering -
http://en.wikipedia.org/wiki/Weathering#Physical_.28mechanical.29_weathering
> Joint - http://en.wikipedia.org/wiki/Joint_%28geology%29
> Scree - http://en.wikipedia.org/wiki/Scree
> Spheroidal weathering - http://en.wikipedia.org/wiki/Spheroidal_weathering
> Chemical weathering - http://en.wikipedia.org/wiki/Weathering#Chemical_weathering
> Sediment - http://en.wikipedia.org/wiki/Sediment
> Particle size - http://en.wikipedia.org/wiki/Particle_size