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!