Chapter 9 – Glacial

Please add your comments about how to improve Chapter 9 here.

21 thoughts on “Chapter 9 – Glacial”

  1. Article about modeling basal sliding (Stearns and van der Veen, 2018, Science v. 361: 273) is important and you might use conclusions to modify a sentence or two about glacial water

  2. The chapter is fine and better as it stands (and my students already use it well), so my suggestions and musings should be taken as things to think about or as asides to remind you of what you know but haven’t put in because it takes more writing/space. Most of the additions or clarifications I muse about are related to the position of words or phrases in the text…and aligning figure caption information with what is said in the text. In general I’d feel a little better if the setup part of the chapter reached a little more broadly to grab the reader about what is coming. I’d also like you to think again about the positioning of some figures and some paragraphs. And I’d like basal water and sediment to have at least a cameo earlier on in the chapter.

  3. below freezing temperatures for much of the year and a mean annual surface temperature of -2°C or less (ah…I see it later, but mebbe good to mention up front)
    frozen ground thaw, lose much of their strength,–active layer has a nice sound to it and it’s in bold on the next page!
    p. 317. Unfrozen material…perhaps unfrozen areas
    at 3800 m…at least patchy at 3700, but perhaps not for long. Aspect also important.
    In the Southern Hemisphere, there is scant permafrost outside of Antarctica…I suppose aerially this is true….but lots in S. America in the drier parts of the Andes and surely on New Zealand on the west side of the south island!
    p. 318. The presence of relict permafrost landforms….and, it turns out, you can get pretty active ground (and landforms) where seasonal freeze/thaw/ice lens processes are active, even when the ground below is no longer frozen.
    backing edges…might that be “back”?
    frost shattering…rate of freezing pretty important and annual temperatures near -6°C seem to be about right for maximum activity
    Photograph 9.28….steep margins might be most characteristic
    p. 320…can get good stone stripes and reasonable patterned ground in other treeless environments where wetting and drying of clays (particularly smectites) encourage heaving
    p. 321. Relict sorted circles are found in areas that were once cold enough…..they also form in areas of active freeze-thaw—no need for permafrost, though it helps!
    rock glaciers are a distinct landform, there may be more than one way….but pretty diagnostic of periglacial climate now or in the past
    p.322. I think it’d be nice to anticipate these (critical) applications with a line in the opening paragraph
    as natural water reservoirs. We like to say water towers! And the water released has very low dissolved solids so it is good for drinking, irrigation, etc
    p. 324. Suggest you use Jack Ridges AJS 2012 paper instead American Journal of Science 312: 685-722
    p.325. development of ice-flow models that included basal….one of the key leaps was how to use the infinite slab model to include erosion of the “banks” by the ice slab. Love this Yosemite story! Part of the effect is provided by the lake-sediment fill?
    p. 326. Plots are dimensionless…..and T is in arbitrary time units
    p. 328. Only 2 “sketch” questions until #37….have them draw or graph some of the things you ask them to describe—it’ll help them solidify their knowledge and force them to look back. And few/none of these are practical questions about the broader geomorphic/climate/societal importance of glaciers….things that will be important to your students. Why are alpine glaciers the canaries in the climate coal mine? What sorts of glacial deposits form good aquifer material? Why are some till plains challenging for development?

  4. p. 306. , reflecting differences in the intensity and character of erosion. Seems likely that subglacial temperature fluctuations above and below freezing promote quarrying and freeze-on of tools, particularly in the ablation zone of temperate ice.
    p. 307. (such as southeastern Alaska). Soft rocks (and good tools from upice) help!
    p. 309. making a positive feedback loop. But digging in effectively raises the ELA…a negative feedback!
    p. 310. Field of view is several kilometers wide. Actually about a kilometer
    Till. Perhaps from near the base of the ice (lodgement) and from englacial and supraglacial sediment as the ice melts (meltout, etc). Meltout tills also tend to be coarser since some of the fine fraction (if there was one) has washed away.
    fills voids in the ice…and next to the ice if there is any sort of local relief. Hence the curse of using the word kame—it can describe any partly washed sediment that was deposited in a cavity with an ice wall (I guess excepting eskers)—hence kame moraines, kame deltas, kame terraces, kamic this and kamic that etc
    p. 311. I love these views of ice contact landforms….but wonder if you need the diagrammatic views of them early in this section. And do you want to mention ice-contact stratified drift?
    Much of Cape Cod,….and the moraine itself is pretty pitted and mainly composed of water-washed sediment (you note later)…particularly compared to the till moraines of the American Midwest.
    Photograph 9.21. Cool shot –where is the lake the delta filled?
    p. 312. bottom brickyards. Never mind aquifers and aquicludes, etc! The subsurface legacy of many places!
    p. 313. I relate to this way of telling the story!! But I do wonder if an integration of these figs. with those of the previous pages might provide a clearer context for, say, eskers. Perhaps you could at least look forward to the diagrammatic views of p. 314. Thanks so much for not allowing the idea of “ground moraine”!!
    p. 314. The presence of a moraine or a zone of ice-marginal features
    p. 315. They can be steep on the up-ice side….I forget what the stats say, but there are lots of symmetrical drumlins as well and some surely were sculpted by subsurface flowing water. Perhaps you can caution your readers slightly?
    head gradients. I suspect that your illustration budget is done, but it’d be nice here somewhere to illustrate a glacier as aquifer material so you could illustrate head….moulin plumbing, uphill water flow, and some of the other concepts you’ve noted along the way
    p. 316. Even river systems and hillslopes far away….never mind shorelines and coral reefs and other far-field recorders

  5. p. 300. critical shear stress (t)…tighten this important section by helping the reader a bit with “critical” as you switch from ice to bed material deformation…where did strength sneak in? Is it in an earlier chapter? My temptation here—I know you thought about it—is to include the simple eqns for basal slip and erosion rate—helps students think about the role of water and rate of flow, etc! You can pretty much add a couple things to Glens….which you have already!
    p. 301. Fig. 9.7 Need some subglacial water here (except in Antarctica) since calving ice is mainly too clean to produce piles of sediment… whereas subglacial tunnels pump immense amounts of sediment into the receiving body of water, building subaqueous fans.—you could also give your floating ice a little sill to buttress on/against. In general you can help set up the arguments here by introducing the water a little earlier.
    Glacial ice flows from the accumulation zone to the ablation zone (Figure 9.4) Suggest putting this statement about “normal” flow back a few pages….just before you start introducing more complex concepts—it is buried here.
    p. 302. I would have thought that any warm-based glacier is likely to surge at times when subglacial cavities and underlying material can’t move the water through fast enough???
    eroded into rock by flowing ice. Make sure here and earlier that you give the soft ice sediment “teeth” so it can actually do work when it flows. I think a phrase or two early (dirty ice does the work) will help prepare the reader as you introduce sediment after you are mainly finished with ice.
    p. 303. The downward movement of ice with different thermal histories and the effects of glacial flow can result in complex patterns of temperature with depth unlike those shown here. Too late in the game to illustrate advection of cold or warm ice?….nicely explained in the text, but an illustration might cement the point for some.
    Glacial hydrology. Might remind reader here that you are talking about warm-based ice and the summer!
    p. 304. Where the substrate is hard and not deformable, such as over much of the Canadian Shield….this is a cold, low K example from Peter, but single tunnels seem to form under a large variety of conditions, particularly where topography encourages formation. For instance, it looks as though the retreating Puget Lobe was drained by a limited number of tunnels…particularly to the north….and this is certainly true of ice retreating from New England. Suggest hedge the wording just a bit
    The amount of meltwater reaching the bed of ice sheets and glaciers is a critical control on both glacial erosion and ice flow….set this idea up earlier!!
    Photograph 9.7. A great pair and thanks for the scale
    p. 305. There are several processes….you need to have sediment in the basal ice to do much of this work. Make sure your students know that it is the deformation of dirty ice that does it

  6. p. 291. Glaciers excavated the Great Lakes…perhaps they helped excavate? (like the Finger Lakes glacial lobes took advantage of older fluvial and hillslope topography)
    deposited the sediment…wonder if you might highlight the deposits (not just landscapes) just a bit more since they control the substrate, permeability and porosity, subsurface flow and some aspects of surface flow in so many areas of North American and northern Eurasia. Highlighting with a phrase or two here helps set up the sections near the end of the chapter.
    permafrost….technically a temperature and the ground…but I think you have it covered.
    p. 292. I don’t think that frozen soil flows much compared to thawed, saturated soil over frozen substrate. Or do you mean glaciers and their load of frozen sediment? Rock glaciers flow….but interstitial ice is only the culprit in some cases….and flow is slow!
    “Quarrying” also below the ice, right?
    controlled by plate tectonics,…probably by pCO2 as well?
    p. 293… induced by the freezing of water….and thawing of ice, etc! Lots of action even in areas where it isn’t cold enough for much thermal contraction…mebbe density driven convection of water helps as well.
    Fig. 9.2. last caption block a good place to remind reader of when the LGM took place
    p. 294…somewhere here you may want to introduce the active layer (it appears and reappears in the next couple of pages)…since most work seems to happen there. Many periglacial environments are dry!
    The ice sheet in section in Fig. 9.2 could be an ice cap! Are ice fields smaller?? You could also say “outlet glacier” again in the text.
    wind carrying snow transported by the wind?
    p. 295. Photograph 9.2 I know it is work, but rough statements about scales might help the observer unfamiliar with glaciers…and would be consistent with most of your other captions
    p. 296. You might want to use “metamorphoses” in the text as well.
    9.3 blue box—meltwater is pretty common as part of the transformation processes and might be mentioned here somewhere. Refer to Fig. 9.4 near the beginning of the energy section or your reader won’t follow.
    p. 297. I do love Fig. 9.4, but I think the extended and wide-reaching discussion here would work better if you started with the ELA and accumulation and ablation zones….and then dug into the complexities of the mass and energy budgets.
    p. 299. Mebbe introduce water at the bed earlier rather than later? Seems like your warm-based glacier would also like some till beneath it. I think that more foreshadowing of the significance of water early would help the reader here and elsewhere.

  7. could be more related to genesis of some landforms. Fig. 9.10 (p. 313) could perhaps be broken down and the formation of kames, eskers, and drumlins could be addressed more closely. Obviously, drumlin formation is debated, but it might be worth discussing and illustrating at least one or two ideas. It might also be worth illustrating how pingos form to compliment the description (students seem to struggle with this concept).

  8. Page 302, last part of first paragraph. “specifically hydraulic head increases that reduce resistance to basal slip.” It would help if the student is reminded of what hydraulic head means here. While most students in my class have taken an intro to hydrology, few have taken an upper level hydrology course at this point.

  9. Page 297, right hand column, last part of 4th paragraph–firn line. This could more clearly be defined as the elevation above which the snow survived the summer melt season

  10. Page 294, right hand column, 2nd paragraph. It would be helpful to define “piedmont” here. I don’t believe that it is defined previously in the text

  11. Figure 9.4 (pg 298) lower right corner. The graphical representation of the position of the ELA with temperature (average July temps) vs. elevation is not intuitive and not well described in the figure caption, specifically the x-axis where temperature decreases from left to right. It would make more sense for temperature to INCREASE from left to right because as the temperature increases, the ELA will rise in elevation. Or is this figure describing what temperature actually does with elevation (decreases as elevation increases)? If so, a clearer explanation in the figure/figure caption would help clarify.

  12. Polygon formation (pg 320) is oversimplified, which makes it hard to comprehend.

  13. Why isn’t ice segregation mentioned in the chapter on weathering? This is an important weathering process that should be introduced along with other cold-climate physical weathering processes. In the glacier chapter it would then only need to be mentioned.

  14. Figure 9.10 (pg 313) is a very informative figure that appears too late in the chapter. It would be more appropriate at the beginning of the chapter (before photo 9.2, pg 295) because many of the landforms and processes shown in the figure are defined many pages before the figure. This leads to some repetition in the text.

  15. In figure 9.13 (pg 321) appears as if the wedge moves from its location during winter to a new, thawed, location during the fall. Not sure if this is on purpose because the year 3 image shows the wedge staying in the same place year after year

  16. p. 311 second sentence on page – text says “plan view” but I believe it should say “plane view” because “plan view” does not make sense.

  17. The first full sentence on page 306 doesn’t make sense. It might be too long to follow, or a collection of incomplete thoughts. Figure 9.6, applying Glen’s Flow Law to strong and weak bed material on page 300 is a bit confusing. The relationship between elevation, distance, and strong verses weak bed is not very clear. Photograph 9.11 on page 307 has faint outlines from the text boxes put on to the photo. A question could be added on albedo, and potentially tie this into how changing climate and volcanism alters the albedo of glaciers. Discussing the orographic effect would also be helpful. On page 315 it is never discussed WHY and what processes are involved in drumlin formation. To fully understand a concept, I like to understand the mechanisms behind why something happens rather than just knowing the it does.

  18. My students felt like the glacier chapter was less grounded in process than the other chapters they have read and that it was more just lists of terms they needed to know the definitions of.

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