Chapter 18
Landforms and Rock Structure
OVERVIEW
This chapter considers how rock properties influence the landforms and drainage patterns
produced by fluvial denudation.
 The Earth’s crust contains a variety of rock types which differ in their resistance to
denudation. More resistant rock tends to form uplands and ridges, while weaker rock
forms lowlands and valleys.
 Rock layers can be tilted, folded, and fractured by tectonic forces to produce a variety
of rock structures. The tilt and orientation of rock layers and fractures are described by
their strike and dip.
 In areas with horizontal strata and an arid climate, fluvial denudation produces vertical
cliffs of resistant rock separated by gentler slopes of less resistant rock. These slopes
surround flat-topped plateaus, mesas, and buttes capped by resistant rock.
 Different rock types and structures tend to produce different drainage patterns or
stream network characteristics. Drainage patterns have some interesting, systematic
geometric properties.
 Areas of horizontal strata usually have broadly branching, dendritic drainage
patterns.
 On gently dipping strata along coastal plains, cuestas form in more resistant rock
while lowland valleys develop in the less resistant rock. The development of
consequent streams across the cuestas and subsequent streams along the lowland
valleys produces a trellis drainage pattern.
 Fluvial denudation of a sedimentary dome produces an annular drainage pattern and
a circular pattern of hogbacks of more resistant rock separated by lowlands of less
resistant rock.
 Linear fold belts of anticlines and synclines are eroded into ridge-and-valley
landscapes, with the more resistant strata forming ridges and the less resistant strata
forming valleys. A trellis drainage pattern is typical of these landscapes.
 A rock face produced by faulting can persist as a fault-line scarp, while a landscape is
worn down by denudation. A subsequent stream often marks the zone of weakness
along a fault plane.
 Tightly folded metamorphic rocks tend to erode to ridge-and-valley landscapes that
are less rugged than those developed in folded sedimentary rock. The resistant
metamorphic rocks of slate and schist form the hill belts, while the less resistant
marble forms the valleys.
 A monadnock is an isolated projection of intrusive igneous rock surrounded by an
eroded plain. Dendritic drainage patterns develop on these eroded batholiths.
 Radial drainage patterns develop in the early stage of erosion of stratovolcanoes. The
advanced stage of erosion produces volcanic necks and radial dikes of resistant
igneous rock.
 The erosion of shield volcanoes results in landscapes of steep slopes and sharp ridges.
Radial consequent streams cut deep canyons into the sides of the extinct volcanoes.
KEY TERMS
strike
dip
plateau
mesa
butte
drainage pattern
bifurcation ratio
dendritic drainage
pattern
trellis drainage
pattern
coastal plain
cuesta
artesian well
aquifer
aquiclude
sedimentary dome
hogback
radial drainage
pattern
ridge-and-valley
landscape
fault-line scarp
monadnock
volcanic neck
STUDY QUESTIONS
What are sequential landforms, and how are their shapes, sizes and arrangements
influenced by rock properties?
2. Sketch a simple diagram to illustrate the concepts of rock strike and dip.
3. Describe a mesa, and discuss the role of rock properties in the development of a
mesa’s distinctive shape.
4. Sketch simple diagrams to illustrate dendritic, trellis, and radial drainage patterns.
Give an example of the conditions under which each is expected to be found.
5. Plot a graph to show how the number of stream segments normally varies with stream
order.
6. Alternating bands of cuestas and lowlands occur on many of the coastal plains of
passive continental margins. Describe these landforms, and discuss the role of rock
properties in their development.
7. What is a hogback? In what type of rock structure do they usually develop?
8. Ridge-and-valley landscapes can develop on two different kinds of rock structures.
What are these rock structures, and how do the characteristics of the ridges and valleys
differ between them?
9. Subsequent streams are often found at the base of fault-line scarps. Why?
10. What is the relationship between a batholith and a monadnock?
11. The denudation of stratovolcanoes and shield volcanoes produce very different
landscapes. How do they differ and why?
1.
CHAPTER QUIZ
Multiple Choice Questions
1. A ridge of resistant rock which develops through the denudation of a sedimentary
dome is called a:
a) monadnock
b) cuesta
c) hogback
d) mesa
2. The angle between a rock plane and the horizontal is termed the:
a) dip
b) trend
c) butte
d) strike
3. The broadly branching drainage patterns that develop on horizontal strata are called:
a) radial drainage patterns
b) annular drainage patterns
c) trellis drainage patterns
d) dendritic drainage patterns
4. Ridge-and-valley landscapes develop through the denudation of:
a) stratovolcanoes
b) anticlines and synclines
c) horizontal strata of coastal plains
d) batholiths of igneous rock
5. Which of the following metamorphic rock types is most likely to form sharp ridges in
an eroded landscape?
a) slate
b) marble
c) quartzite
d) gneiss
True/False Questions
The valleys in eroded fold belts are always associated with synclines. (T/F)
The denudation of shield volcanoes produces rugged mountains with sharp-crested
divides and deep canyons. (T/F)
3. A mesa is smaller than a butte. (T/F)
4. A stratovolcano is an initial landform. (T/F)
5. A consequent stream develops in zones of weak rock following the pattern of rock
exposure. (T/F)
1.
2.
Short Answer Questions
Why do arid landscapes eroded out of horizontal strata typically have vertical cliffs
separated by more gentle slopes?
2. Why do dendritic drainage patterns typically develop on both horizontal strata and on
large batholiths?
1.
Short Essay Questions (1 - 2 paragraphs)
Describe the landforms typically associated with normal faulting, and discuss why
these landforms continue to be expressed in the landscape over long periods of
denudation.
2. Assume that you have the following sequence of sedimentary strata  sandstone,
limestone, and shale. First, describe the landforms that would result if these strata
were horizontal and subjected to denudation under an arid climate. Second, speculate
as to the landforms that would develop if the same strata were tilted and subjected to
denudation under an arid climate. Use diagrams to illustrate your answer.
1.
Internet Resources
1. Osage Cuestas in Kansas:
<http://www.kgs.ukans.edu/Extension/cuestas/cuestas.html>;
<http://crude2.kgs.ukans.edu/Physio/osage.html>
2. The Eastern Ridges and Lowlands of Wisconsin:
<http://www.wisconline.com/wisconsin/geoprovinces/easternridges.html>
3. Excellent photos of structural and other landforms of the US: <http://ogu.t.utokyo.ac.jp/ame/ame-e.html>
4. Tectonic landforms from space:
<http://daac.gsfc.nasa.gov/DAAC_DOCS/geomorphology/GEO_2/GEO_CHAPTER
_2_TABLE.HTML>
5. A very good slide show on volcanic and tectonic landforms:
<http://www.lbcc.cc.or.us/geography/physical/volcanicpp_files/v3_document.htm>
6. Remote Sensing and Photo Interpretation: Tectonic/Volcanic Landforms:
<http://tutorial.core.ipp.pt/mirrors/Tutorial/Sect17/nicktutor_17-3.html>
7. International Association of Geomorphologists image gallery including a number of
tectonic and weathering landforms: <http://www.geomorph.org/gt/gtgal.html>
8. Glossary of geologic terms with some good diagrams of tectonic features:
<http://geollab.jmu.edu/vageol/outreach/fieldtrips/Batt/Glossary.htm>
9. Death Valley National Park geology image gallery containing a photos of
tectonic/structural landforms:
<http://www.aqd.nps.gov/grd/usgsnps/deva/gallery.html>