Earth Science Q - Resistant Rock Layers ?

[EdBarnes]

Hi - I'm struggling to understand the attached question from a take home lab.   If anyone has suggestions, clarification, or explanation - I would greatly appreciate it.  Thank you

 

 

 

[swansont]

What’s your attempt at answering?

Do resistant layers erode faster or slower than the less resistant layers?

[studiot]

Just now, EdBarnes said:

Hi - I'm struggling to understand the attached question from a take home lab.   If anyone has suggestions, clarification, or explanation - I would greatly appreciate it.  Thank you

When thinking about swansont's comment ask yourself  "resistant against what ?"

Hint the last of your pictures rather gives the game away.

[EdBarnes]

I would think that resistant layers would erode slower - simply because of the word "resistant".   The last picture appears to show water, which I imagine would expedite the erosion of any layer.  In the last image, it appears that the top layer is most resistant, but it's definitely not clear to me.  I appreciate the responses.  

[studiot]

Just now, EdBarnes said:

I would think that resistant layers would erode slower - simply because of the word "resistant".   The last picture appears to show water, which I imagine would expedite the erosion of any layer.  In the last image, it appears that the top layer is most resistant, but it's definitely not clear to me.  I appreciate the responses.  

I think you are clear what is being eroded or weathered, but did you think about my question ?

In each of the three pictures what agent is dong the eroding.

Note it is probably different in each case.

[swansont]

1 hour ago, EdBarnes said:

I would think that resistant layers would erode slower - simply because of the word "resistant".   The last picture appears to show water, which I imagine would expedite the erosion of any layer.  In the last image, it appears that the top layer is most resistant, but it's definitely not clear to me.  I appreciate the responses.  

That would be my (inexpert) analysis. It’s exposed directly to the water and yet it erodes less.

In #2, do you expect sharp corners to last in erosion/weathering?

[EdBarnes]

It's clear that in the last image the agent causing erosion is water.  I suspect wind in the second image and perhaps glacier or ice in the first ?   

[swansont]

8 minutes ago, EdBarnes said:

It's clear that in the last image the agent causing erosion is water.  I suspect wind in the second image and perhaps glacier or ice in the first ?   

I’d guess water, as in a river, and then wind. It looks like the Grand Canyon in cross-section

[studiot]

Hello Ed,

You are clearly near the beginning of your studies here, but it would be useful if you were to indicate your interest in physical geography / physical geology / geomorphology is.  Especially if you are going to post more questions for clarification. It really is a fascinating subject.

The three diagrams you posted were from an older era and the subject has moved on since.
In those days the view was rather narrow and static. Today we try to look at such questions in a wider sense, both in how the particular landforms developed and fit in both with their surrounding areas on the ground and our best theoretical work on the subject.
I note that the three diagrams (which could easily have been drawn by Arthur Holmes a very famous pioneer) have been carefully edited to avoid showing any explanation, for the purpose of making them into a question.

I take it you are aware that all the rocks on Earth can be classified into sedimentary or igneous (volcanic).

All three diagrams could be formed from either types of rock by 'denudation processes'. Denudation is the overall term for the general process by which earth and rock  is detached from the main body of material and transported away from the site to somewhere else.

Swansont has suggested that the waterfall might be formed like the ones on the Colorado river in the Grand Canyon.

These layers here are mostly volcanic and look like the ones in the Rio Grande picture.

 

Here, as with the Grand Canyon there is a large scale upper plateaux or mesa, heavily dissected by a major river in an arid area.

More can be seen here

https://www.nps.gov/grca/learn/nature/grca-geology.htm

 

The whole area has been uplifted and is a bit like the simplified diagram below. Note the timeline goes from right to left.

 

The final stages of this process, which have not yet happened, look like this butte in Utah.

Note here the pile of debris at the bottom, which has not yet been transported away.

 

This could also be as the first diagram of your question.

 

The waterfall diagram shows nor canyon sidewalls , more like Niagara, which is forming on sedimentary rock.

 

In your middle diagram the resisant layers could be part of an anticline, with the top worn away, as with this section of the Welsh Borders.

 

[EdBarnes]

 

studiot,

Thank you very much for this detailed response - this is extremely helpful.   I'm an honors earth science student, so while I  find the subject fascinating, I'm just beginning my studies and I'm beginning to question my teachers methods, as the material on that sheet was not covered during our classroom sessions.  I will update the thread when my lab is returned.  I really appreciate everyone taking time to respond - it's very much appreciated !

[studiot]

2 hours ago, EdBarnes said:

 

studiot,

Thank you very much for this detailed response - this is extremely helpful.   I'm an honors earth science student, so while I  find the subject fascinating, I'm just beginning my studies and I'm beginning to question my teachers methods, as the material on that sheet was not covered during our classroom sessions.  I will update the thread when my lab is returned.  I really appreciate everyone taking time to respond - it's very much appreciated !

Good on you for your choice of subject.

Perhaps your lecturers are trying to make their students think ?

At third level you need self directed learning (reading around the subject) more than ever.
You learn almost as much from your fellow students as from your lecturers, especially in a subject that devotees are passionate about.

Also this subject requires a wide ranging scientific background, so much of the first year is spent bring students from disparate backgrounds up to a required common level. The pace and standard ramps up after that.

From the times of your posting I deduce that you are probably in OZ or NZ.

This book, from Oxford University Press has most of the examples set in this continent.

He also wrote a smaller first year university textbook about the subject.

Sadly Prof Selby passed in 2018.

 

But remember ScienceForums when you want to discuss something.

You can post more generally in the Earth Science section, the Homework section has special rules so we are not allowed to answer set work directly.

 

Edited 21 hours ago by studiot