Key Concepts in Geomorphology – ideas for revision
Chapter 3 – Weathering
Please add your comments about how to improve Chapter 3 here.
9 thoughts on “Chapter 3 – Weathering”
Hi Guys. Enjoying the book. Sorry for typos below. I agree that this Chapter is jammed packed. Splitting into weathering processes, vs soils overall might help. I would put soils first – then get into the details of weathering. Other comments below. Missy
INTRO SECTION
– I would not say that different environments favor physical over chemical. Instead, one might be more obvious than the other. I think it is misleading to say that chemical weathering dominates in moist environments. There is amble evidence (see review in Brantley2017) that they co-evolve in those climates. I think this is an atequated view now, that seems to be dispersed throughout the intro to the chapter. I think fig 3.1 is a gross oversimplification and these days is just plain confusing or not right. Perhaps delete.
– Same with the idea that freezing dominates mechanical weathering. Lots of data out now that thermal (ahem Eppes papers as well as recent ones by Collins, 2018) is important, not to mention topographic/tectonic stresses themselves (ala Martel, Moon, St. Claire). If it were freezing, then erosion rates on outcrops (ala Bierman and Portenga) would presumably show gradients with temp, and they do not.
– It is not known if the growth of tree roots per se is what opens fractures; better: trees serve to open fractures – we don’t know exactly how.
PHY W Section
– The section on exfoliation needs to be updated with ideas from convexity-tectontics interactions (ala Martel) as well as thermal stress(Collins et al., 2018)). It is not really a done deal as most textbooks present it. The Twain Harte (search Twain Harte rock cracking on YouTube) thing should likely be a Vignette!
– Could add Brantley’s et als work that shows that precip of Fe oxides, for example cracks things.
– For thermal, it is not just in EarthDeserts where n-S cracks are found – mars (Eppes et al., 2015)and North Carolina and Pennsylvania )(Aldred et al., 2015)
– Here is a bias – feel free to take or leave – but I think it would be worthwhile to differentiate the STRESSES that lead to Mechanical weathering from the cracking process(es) themselves and to introduce subcritical cracking. See Section 2 of (Eppes and Keanini, 2017) for a review. Obviously I think we have really missed out on this important distinction as weathering scientists. I am happy to help write a paragraph or 2 there.
I skipped the Chem weathering section
SOILS
– Under soil development processes in the 1st paragraph, it would likely be helpful for students if you tie in this language back to chemical and physical weathering – so they will know it is part of it.
–
Aldred, J., Eppes, M. C., Aquino, K., Deal, R., Garbini, J., Swami, S., Tuttle, A., and Xanthos, G., 2015, The influence of solar‐induced thermal stresses on the mechanical weathering of rocks in humid mid‐latitudes: Earth Surface Processes and Landforms.
Collins, B. D., Stock, G. M., Eppes, M. C., Lewis, S., Corbett, S., and Smith, J., 2018, Thermal inflouences on spontaneous rock dome exfoliation: Nature Communications.
Eppes, M. C., and Keanini, R., 2017, Mechanical Weathering and Rock Erosion by Climate‐Dependent Subcritical Cracking: Reviews of Geophysics.
Eppes, M. C., Willis, A., Molaro, J., Abernathy, S., and Zhou, B., 2015, Cracks in Martian boulders exhibit preferred orientations that point to solar-induced thermal stress: Nat Commun, v. 6.
–
Page 59 and 61; sediment generation versus sediment yield
About the statement that ‘bedload is either disregarded or assumed as 10 % of suspended load’, I know that this is a general rule of thumb, but I believe that the ratio of suspended load to bedload is totally dependent on the type of the river and varies case by case. The rule of 10 percent might be true for suspended sediment dominant rivers and not for bedload Dominant Rivers. For instance, for the Guadalupe River in Texas, my measurements showed that the river is bedload dominant and suspended sediment can be ignored.
on photo 3.18 add label for silcrete capstone
Add soil horizon labels to photos in 3.10
It also might be worth mentioning where laterites and ferricretes tend to form (tropical to sub-tropical areas).
With respect to clays and soils, it might be worth mentioning by name some other common soil classification systems (USCS and AASHTO) and why the emphasis on these is largely concerned with ascertaining “plasticity” via Atterberg limits, which is a function of the amount and type of clay minerals present. Many students who go on to work with engineers, in environmental site assessment, or in geotechnical investigations use these systems and this relates directly to clay fraction.
Perhaps a bit more mention of applications of weathering and soils would. For instance a discussion of pyrite weathering (which involves dissolution, hydrolysis, and oxidation) to eventually produce acid mine/rock drainage might be one helpful example. Additionally, soils containing sulfides such as pyrite can also expand as secondary sulfates are formed. Those are a few examples that I use.
A lot of important and kind of complex processes packed into this chapter. Might be beneficial to divide it into two, less dense, chapters. One focusing on weathering and a second focusing on soil. The soil chapter could still draw on weathering processes but then both chapters could fully explain key concepts without being rushed or overwhelming.
A lot of the sections were a bit dense in this chapter, so additional photos and figures would help breakup the pages as well as better explain some of the concepts. The differing effects of freshwater verses rain water on erosion could be a good question. I thought that this chapter was a bit denser and wordier than the others. It would be nice if you could try to simplify some of the explanations or supplement with more figures.
University of Vermont
Hi Guys. Enjoying the book. Sorry for typos below. I agree that this Chapter is jammed packed. Splitting into weathering processes, vs soils overall might help. I would put soils first – then get into the details of weathering. Other comments below. Missy
INTRO SECTION
– I would not say that different environments favor physical over chemical. Instead, one might be more obvious than the other. I think it is misleading to say that chemical weathering dominates in moist environments. There is amble evidence (see review in Brantley2017) that they co-evolve in those climates. I think this is an atequated view now, that seems to be dispersed throughout the intro to the chapter. I think fig 3.1 is a gross oversimplification and these days is just plain confusing or not right. Perhaps delete.
– Same with the idea that freezing dominates mechanical weathering. Lots of data out now that thermal (ahem Eppes papers as well as recent ones by Collins, 2018) is important, not to mention topographic/tectonic stresses themselves (ala Martel, Moon, St. Claire). If it were freezing, then erosion rates on outcrops (ala Bierman and Portenga) would presumably show gradients with temp, and they do not.
– It is not known if the growth of tree roots per se is what opens fractures; better: trees serve to open fractures – we don’t know exactly how.
PHY W Section
– The section on exfoliation needs to be updated with ideas from convexity-tectontics interactions (ala Martel) as well as thermal stress(Collins et al., 2018)). It is not really a done deal as most textbooks present it. The Twain Harte (search Twain Harte rock cracking on YouTube) thing should likely be a Vignette!
– Could add Brantley’s et als work that shows that precip of Fe oxides, for example cracks things.
– For thermal, it is not just in EarthDeserts where n-S cracks are found – mars (Eppes et al., 2015)and North Carolina and Pennsylvania )(Aldred et al., 2015)
– Here is a bias – feel free to take or leave – but I think it would be worthwhile to differentiate the STRESSES that lead to Mechanical weathering from the cracking process(es) themselves and to introduce subcritical cracking. See Section 2 of (Eppes and Keanini, 2017) for a review. Obviously I think we have really missed out on this important distinction as weathering scientists. I am happy to help write a paragraph or 2 there.
I skipped the Chem weathering section
SOILS
– Under soil development processes in the 1st paragraph, it would likely be helpful for students if you tie in this language back to chemical and physical weathering – so they will know it is part of it.
–
Aldred, J., Eppes, M. C., Aquino, K., Deal, R., Garbini, J., Swami, S., Tuttle, A., and Xanthos, G., 2015, The influence of solar‐induced thermal stresses on the mechanical weathering of rocks in humid mid‐latitudes: Earth Surface Processes and Landforms.
Collins, B. D., Stock, G. M., Eppes, M. C., Lewis, S., Corbett, S., and Smith, J., 2018, Thermal inflouences on spontaneous rock dome exfoliation: Nature Communications.
Eppes, M. C., and Keanini, R., 2017, Mechanical Weathering and Rock Erosion by Climate‐Dependent Subcritical Cracking: Reviews of Geophysics.
Eppes, M. C., Willis, A., Molaro, J., Abernathy, S., and Zhou, B., 2015, Cracks in Martian boulders exhibit preferred orientations that point to solar-induced thermal stress: Nat Commun, v. 6.
–
Page 59 and 61; sediment generation versus sediment yield
About the statement that ‘bedload is either disregarded or assumed as 10 % of suspended load’, I know that this is a general rule of thumb, but I believe that the ratio of suspended load to bedload is totally dependent on the type of the river and varies case by case. The rule of 10 percent might be true for suspended sediment dominant rivers and not for bedload Dominant Rivers. For instance, for the Guadalupe River in Texas, my measurements showed that the river is bedload dominant and suspended sediment can be ignored.
on photo 3.18 add label for silcrete capstone
Add soil horizon labels to photos in 3.10
It also might be worth mentioning where laterites and ferricretes tend to form (tropical to sub-tropical areas).
With respect to clays and soils, it might be worth mentioning by name some other common soil classification systems (USCS and AASHTO) and why the emphasis on these is largely concerned with ascertaining “plasticity” via Atterberg limits, which is a function of the amount and type of clay minerals present. Many students who go on to work with engineers, in environmental site assessment, or in geotechnical investigations use these systems and this relates directly to clay fraction.
Perhaps a bit more mention of applications of weathering and soils would. For instance a discussion of pyrite weathering (which involves dissolution, hydrolysis, and oxidation) to eventually produce acid mine/rock drainage might be one helpful example. Additionally, soils containing sulfides such as pyrite can also expand as secondary sulfates are formed. Those are a few examples that I use.
A lot of important and kind of complex processes packed into this chapter. Might be beneficial to divide it into two, less dense, chapters. One focusing on weathering and a second focusing on soil. The soil chapter could still draw on weathering processes but then both chapters could fully explain key concepts without being rushed or overwhelming.
A lot of the sections were a bit dense in this chapter, so additional photos and figures would help breakup the pages as well as better explain some of the concepts. The differing effects of freshwater verses rain water on erosion could be a good question. I thought that this chapter was a bit denser and wordier than the others. It would be nice if you could try to simplify some of the explanations or supplement with more figures.