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Chapter 17
Landforms and Rock Structure
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.