Geography 455 Applied Climatology Lecture 25 Landforms Needs: A. Introduction 1. Landforms--the result of the interplay between internal and surface processes 2. Early examples of climate control of landforms a. Glacial terrain--Agassiz b. Arid regions--Penck c. Humid mid-latitudes--Davis 3. Oversimplifications of climatic geomorphology (need to explain how spatial and temporal variations of climate control geomorphic processes, and how they create a range of distinctive landforms a. Relationships difficult to test b. Problems of scale c. Uncertainties of the relationship between surface processes and landforms B. Climate and Geomorphological Processes 1. Global and Regional Scale a. Temperature--cold areas produce physical weathering (freeze-thaw), warm areas, especially with moisture promote chemical weathering b. Seasonality--fluvial erosion rates higher in seasonal climates 2. Local scale relationships harder to verify a. Thresholds for different processes vary with a number of factors including gradient, slope length, and vegetation cover C. Climate Change and Landforms 1. Glaciation--example of how landform assemblages retain the imprint of one or more major changes in climate 2. Sensitivity--how much a landscape will respond to external stimuli by changing its forms 3. Lag time--period between new external stimulus and landform response 4. Relaxation time--time required for the input to result in a characteristic landform 5. General examples a. Highly sensitive landscapes and short duration (but high magnitude) climate changes may yield a complex of transitional forms, but few characteristic landforms b. Low sensitivity landforms (like plateaus) will tend to retain their form 6. Specific examples a. Quaternary glacial-interglacial cycles as shown in ice core-ocean sediment analysis b. Raising and lowering of sea and lake levels (Lake Michigan dunes) Geography 455 Lecture 25 Landforms page 2 c. Erosional rates versus uplift in the Himalayas mountains--effects of multiple glaciation superimposed over tectonic forces d. Some of the driest regions in the world today were once traversed by major rivers--based on evidence of gravels left behind in North Africa e. Wind blown Loess (silt) deposits produce impressive bluffs in China and parts of North America in response to glacial climate changes f. Relic lakes of interior Australia have provided a detailed record of landform evolution and human occupation over about the last 40,000 .