Page 471 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 14 Weathering, Karst Landscapes, and Mass Movement 435
(a) Oxidation of iron minerals produces these brilliant red colours in the sandstone formations of the cliffs on the north shore of Prince Edward Island.
▲Figure 14.13 Oxidation processes in soil. [Mary-Louise Byrne.]
cemeteries (Figure 14.14). In environments where ade- quate water is available for dissolution, weathered lime- stone and marble take on a pitted and worn appearance. Acid precipitation also enhances carbonation processes (see Focus Study 3.2, Acid Deposition: Damaging to Ecosystems).
Karst topography
In certain areas of the world with extensive lime- stone formations, chemical weathering involving dis- solution of carbonates dominates entire landscapes (Figure 14.15). These areas are characterized by pit- ted, bumpy surface topography, poor surface drain- age, and well-developed solution channels (dissolved openings and conduits) underground. In landscapes of this type, weathering and erosion caused by ground- water may result in remarkable mazes of underworld caverns.
These are the hallmark features and landforms of karst topography, named for the Krš Plateau in Slovenia (formerly part of Yugoslavia), where karst processes were first studied. Approximately 15% of Earth’s land area has some karst features, with out- standing examples found in southern China, Japan, Puerto Rico, Jamaica, the Yucatán of Mexico, Canada, and the United States.
(b) Red humo-ferric Podzolic soil is coloured by the sandstone parent material common to most of Prince Edward Island.
▲Figure 14.14 Dissolution of limestone. A marble tombstone is chemically weathered beyond recognition in a Scottish churchyard. Marble is a metamorphic form of limestone. Readable dates on sur- rounding tombstones suggest that this one is about 230 years old. [Bobbé Christopherson.]
Georeport 14.2 Weathering on Bridges in Central park, nyC
In New york City’s Central Park, 36 bridges are built out of various rock types from sources across the U.S. Northeast and Canada. For more than 140 years, physical and chemical processes have weathered these bridges. As air pollution from the
burning of fossil fuels has increased, acidity in rain and snow has hastened weathering rates, a problem compounded by the use in winter of salt on the roads crossing the bridges. Decorative design elements on the bridges are now disappearing as weathering tears at the surface rock. Some heavily weathered sandstone blocks have had to be replaced by cast concrete.