Geology 12 Presents Sedimentary Rocks Weathering and Erosion.
An introduction to the weathering And erosion of rocks and rock art.
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Transcript of An introduction to the weathering And erosion of rocks and rock art.
ROCK ART STABILITY INDEX (R.A.S.I)
An introduction to the weatheringAnd erosion of rocks and rock art
First, Let’s Define Rock Art…
There are several types:
Pictographs Petroglyphs Geoglyphs Intaglios
Pictographs
Images Painted on to the Surface of a Rock
Petroglyphs
Images carved or etched into rocks
This image is from the Petrified Forest National Park, in AZ
Geoglyphs
Also called Rock alignments
These are rocks placed on the ground to form a pattern or image
Image: www.chile.ca
Intaglio
Dirt, rock, or material removed in order to form an image
Image: Bureau of Land Management
So, What is R.A.S.I&
Why Should I Care? R.A.S.I. Stands
for: Rock Art
Stability Index
This helps us tell how much danger the rock art is in of being lost…
Why Should I care? Rock Art is a form
of a Cultural Resource.
It tells us about : Native American
People and Cultures
People who have come and gone in the past
It gives us an archaeological record
How Old IS it? Age of the rock art
varies from 100 years or less to several thousand years old.
The older rock art was carved before the invention of modern tools
Rocks were used as tools, and images were pecked into the rock by hand.
Once it’s Gone…
Why is it in Danger?
Rock Art is a precious, natural resource that is not renewable –
Erosion Weathering Vandalism Theft
It’s Gone Forever…
UNLESS…
We Can Preserve it in Some Way
This is where RASI comes in…
We take photos…
We analyze the danger the rock art is in of being lost
We report it to the National Park Service
Then What?
The information we collect is put into a Database…
Then, The National Park Decides
How to go about Preserving The Rock Art
Why Am I Learning This?
Research Shows… Students learn
better when they apply something they learn
This gives a hands on learning opportunity
It’s More Fun This Way
You will be looking at the panel in a few ways..
Don’t panic, these will be explained as you go along…
The geological setting Which is the area surrounding
the panel
Then general weakness of the panel itself
Large erosion events These are major events about
to happen
Small erosion events on the panel – this is where you get up close to the panel and look for smaller types of weathering
Rock Coatings actually on the panel
Vandalism and other issues
Fissures – Cracks in the Rock
Dependent on stone lithification
Goes along with the bedding plane
Independent of Stone lithification:
Goes against the bedding plane of the rock
More Examples:
Changes in Textural Anomalies
The texture of the rock has banding, spots, or concretions
Rock Weakness –Moh’s Hardness scale
Weaknesses of the Rock Art Panel – this is looking at the
entire panel Fissuresol
dust that gets into the cracks of rocks and weakens it from expansion and contraction during temperature changes
It leaves a ‘scar’ when the rock breaks off
The orange and black is the dust coating left from the break
Roots Look at the
panel, and see if there are roots growing in the panel
The second part asks if there are plants on or near the panel
Scaling & Flaking Scaling
pieces coming off that are a few cm thick – like the width of a hand
Flaking
smaller sizes pieces flaking off – about the thickness of a corn flake or smaller
Splintering
Fissures follow stone structure –
Many in layers
Looks like a book that has gotten wet
Undercutting This is where a
large portion of the rock or soil is missing beneath the panel – Usually caused by water flow
Weathering Rind Development Weathering
Rind – Looks kind of
like an orange peel type texture
Bumpy, uneven texture
Included a picture without weathering rind to demonstrate the difference.
Evidence of Large ErosionEvents on and Below
The Panel
Now you are going to look around the panel
Identify Larger Erosion Events
These are things you can see from a short distance
Anthropogenic Activities(Anthro – Human)
This refers to any current activities by people
Near a hiking trail?
Trash around?
Vandalism?
Judge this by how much of these and similar activities are happening around the site
Smaller Events On the Panel
This is where you get up close and personal to your panel
These are events on a smaller scale
Sometimes your really need to look up close to be able to see these
Abrasion
From Sediment Transport by Water
Water flow carries dirt, sand, and debris,
This causes rocks to wear down
If there is rock art on a rock that is in the path of water, it will slowly disappear
AnthropogenicCutting
Includes Carving Chiseling Bullet impact Other impact
Does NOT include:
The Rock Art itself
Note about classification:
If it’s 50 years old or older: Artifact
If it’s 100 years old or older: Archaeological
Aviolization Pitted or
Honeycombed appearance
Usually in ‘clusters’ not just one pit/hole
Tends to continue to expand and merge together
Crumbly Disintigration
This is where parts of the rock are crumbling off
Texture of Feta Cheese
Can look ‘Powdery’
Flaking
Single or Multiple
Millimeter-scale
Harder to see
Get up close for this
Flaking of the Weathering Rind
Even Smaller Than Flaking
Small flakes in the Weathering Rind
We Saw the Formation of Weathering Rind in a Previous Slide
Granular disintegration
Similar to Crumbly Disintegration
Smaller, sand size debris left over
Most frequently sandstone and granitic
Lithobiont pitting
Lithobionts are a Fungus that Grows on the Rock and Eats it
Leaves a Pitted Appearance in the Surface of the Rock
Can Look Similar to Aveolization
Lithobiont release
when the "dam" of weathered rind decayed rock erodes
Leaves a visible scar in the rock
Happens when the lithobionts die
Loss parallel to stone structure
bedding or foliations
Rock Cracks and Separates
Rock coating detachment
Usually incomplete
Includes paint material in pictographs
Coating on rock starts to detach
Rounding of petroglyph edges (or blurring of pictograph images)
Take the assumption that they were crisp and sharp when created
Can be blurred a little or almost
un-discernible
Rounding of petroglyph edges (or blurring of pictograph images)
Take the assumption that they were crisp and sharp when created
Can be blurred a little or almost
un-discernible
Textural Anomaly Features Erode Differentially
Clay lenses
Cementation
Differences
Nodules
Rock coating present
Rock coatings vary
Most rock will have some coating
Rock coatings help protect the rock
This is a negative number on your assessment sheet
Case Hardening
Similar to Rock Coatings
But becomes thicker
If you knock on it, it will sound hollow
Although it protects the rock, when it detaches, there is loss
Step 1
Log Into Course Assign
Answer Questions
Submit your Lab
Now, Go RASI!