Hallam Ch. 4: THE ICE AGE

Terms

As you read this chapter, watch for and define the following terms. (Definitions are provided for terms not discussed in the chapter.)

     

     

  1. Cirque: a great bowl-like ampitheater at the top of a U-shaped valley where a glacier formed.

     

  2. Horn: a mountain peak surrounded by several cirques.

     

  3. Hanging valley: a U-shaped valley carved by a glacier that empties into a deeper U-shaped "trunk" valley, often with a tall, beautiful waterfall.

     

  4. Arete: a steep, narrow, spine-like ridge separating two adjacent hanging valleys.

     

  5. Tarn: a lake in a hanging valley residing in a depression scooped out by a glacier that has since melted.

     

  6. Till

     

  7. Erratic boulders (for an example, see the misunderstood picture in Lyell, p. 260):

     

  8. Lateral Moraines

     

  9. Medial Moraines

     

  10. Terminal Moraines: Till deposited by a glacier upon melting at its lowest elevation or southernmost latitude.

     

  11. Proglacial lake: a lake formed behind a terminal moraine, which serves as the dam.

     

  12. Drumlins: till deposits shaped into stream-lined "drumsticks" by the advance of glaciers. Their long-axes are parallel to the direction of glacial advance. Steeper slopes are upstream, gentler slopes downstream (why?--compare drift islands in the Ganges delta).

     

  13. Esker deposits: deposits formed by streams flowing underneath the ice.

     

  14. Kames: Mounds of gravel left at the end of streams flowing underneath the ice.

     

  15. Kettle holes or ponds: vacuities in glacial areas left by chunks of ice which have melted.

     

  16. Outwash plain: finer, stratified sediment deposited in a relatively flat area, carried by streams issuing from glaciers.

     

  17. Fjord: an estuary in a drowned glaciated coastal valley, common in Scandinavia, Alaska, and (to a lesser extent) Maine. Estuaries and fjords reflect the rise of sea level associated with melting after the last ice age.

     

  18. Raised beaches: Due to the falling of sea-level as more water became tied up in ice-sheets. Sometimes raised beaches form a series of stairsteps, each step representing a period of time with a different sea-level.

     

  19. Pleistocene Period: The most recent geological period in which major ice ages occurred. See the geological column for an overview.

Focus Questions

     
  1. Define alluvial and diluvial.
    Why did many early geologists, including William Buckland and Adam Sedgwick, distinguish between these two kinds of deposits?
    How did the phenomena assigned to these two categories differ in appearance?

     

  2. What was the Drift Theory?
    What phenomena did it account for?
    What empirical evidence could be cited to support it?
    Who were its early and principal advocates?

     

  3. How did Saussure account for the presence of large granite and schist boulders on the flanks of the Jura Mountains? What evidence did he have to support his views?

     

  4. How did James Hutton and John Playfair account for the same boulders, based on their reading of Saussure's descriptions?

    (It is interesting to note that Hutton never visited what he would have regarded as glacier-sculpted landforms, although much of the phenomena of his Scottish homeland was--unknown to him--due to glaciation.)

     

  5. Leopold von Buch demonstrated that granite erratics in northern Germany originated from where?

     

  6. Describe the views and "evangelistic activity" of Louis Agassiz. Was Agassiz successful in persuading the world of his Ice Age theory? Why or why not?

     

  7. What evidence did Agassiz offer for the occurrence of ice sheets over most of the European continent?

     

  8. What evidence did Agassiz offer for the simultaneous extinction and mass destruction of animal life during the Eiszeit or Ice Age?

     

  9. What evidence led Agassiz to conclude that glaciers had once covered most of Scotland, Ireland, and England? Describe the specific phenomena that supported this inference.

     

  10. What was Lyell's view? Over the long run, did he remain committed to the Drift theory or to the Ice Age theory?

     

  11. What was William Whewell's objection to an Ice Age based on the physics of a gradually cooling earth?

     

  12. What evidence did Arnold Guyot find? Why did this undermine the drift theory in favor of glacial action?

     

  13. What evidence did T. F. Jamieson observe? Why did this undermine the drift theory in favor of glacial action?

     

  14. One of the supporting evidences for the drift theory was the existence of marine shells in glacial till, suggesting that the land was once inundated by the sea. How did Croll and Tiddeman account for this?

     

  15. How did Charles Darwin explain the origin of the "Parallel Roads of Glen Roy"? How are they explained now?

     

  16. Many of Agassiz' ideas were extravagant, including those which turned out to be true.
    Did Agassiz invoke a glacier to explain the phenomena of the Amazon River valley?
    Did Agassiz argue for a single, universal ice sheet covering all of Europe or for several distinct Ice Ages moving from different centers of origin?

Questions for Further Analysis

     
  1. Glaciers are continuous, abrasive conveyor belts transporting unimaginable amounts of rock and debris and carving up the land they pass through. How have glaciers shaped the topography and phenomena of Glacier National Park in Montana? List examples after viewing the slides, and find examples on the topographical maps provided in class.

     

  2. How far south in the United States did glaciers reach during the last ice age?

     

  3. What evidence might be observed that would suggest more than one recent ice age? How could you prove the occurrence of multiple periods of glaciation?

     

  4. Did ice ages occur in geological periods other than the Pleistocene? Or are they relatively rare, geologically speaking? If they are common, how common are they?

     

  5. Derek Ager argues that "The evidence clearly indicates that, for most of [its] history, the earth was a milder and more pleasant place to live than it is at the present day. We are living in the aftermath of the Pleistocene catastrophe and, even without the concern of the ecologists about man burning fossil fuels, there is no doubt--on purely geological grounds--that global warming must come. With it there will be melting of the polar ice sheets, renewed marine transgressions across the continents and the renewed deposition of platform carbonates." {\i The New Catastrophism}, 1993, pp. 63-64.

    Does Ager's argument make sense? Is there another possible position? How do we know that the multiple glaciations of the Pleistocene have ceased? Might we be poised between recurring episodes of a continuing ice-age, in which we could expect a global cooling associated with a return of glaciers across America and Europe?
    What kind of evidence would help you decide between these two positions?