Not far from Lima, Peru, rises a remarkable landscape of intricately fluted pillars, honeycombed columns, and creviced towers topped by balanced rocks. The surrounding flat fields further emphasize the extraordinary relief of this rock forest, or Bosque de Rocas, which is a product of both intense heat and extreme cold.
The Bosque de Rocas is in the foothills of the Andes, where there are numerous volcanoes. Millions of years ago the volcanoes exploded and covered vast areas with what eventually became a coating of ignimbrite, or hardened ash, as well as other kinds of volcanic debris.
Near the small village of Huar6n, the volcanic rocks formed a plateau on top of layers of different kinds of sandstone, limestone, and conglomerate. This fantastic forest of stone developed on the edge of the rocky plateau and on the slopes of the neighboring valleys.
Because ignimbrite is a porous rock, it is particularly susceptible to frost erosion. About 20,000 years ago, during the last ice age, there was snow on the plateau year-round (today temporary glaciers develop there only during the cool season). As freezing and thawing took place, meltwater filtered into cracks in the porous rock and froze. There its erosive power was intensified, since freezing water always expands, causing rock to crumble along its joints.
Eventually, when the climate here became warmer, the ice melted away, and what remained was the incredibly eroded rock formations, sculpted into deeply grooved towers and pinnacles. The extraordinary topography of the Bosque de Rocas was most likely formed in a relatively short time, geologically speaking, that is—perhaps in one or two millennia.
Coral Reefs: Where and How They Grow
A coral reef can grow to enormous size: the Great Barrier Reef extends for nearly 1,300 miles (2,100 kilometers) along the northeastern coast of Australia. Yet its basic components are tiny animals—fleshy, tentacled creatures with skeletons of calcium carbonate (the substance that makes up limestone). Reef-building corals generally reproduce by budding off new individuals that remain attached to the “parent.” Once a colony forms, it grows upward and outward, building on the skeletons of dead coral.
Microscopic plants live in the soft tissues of coral animals. Because these plants require light for photosynthesis, living coral occurs only in water less than 200 feet (60 meters) deep. Living reefs also require clear, warm, turbulent saltwater; reefs do not develop along the western coasts of continents, where cold currents prevail. Sarah loves her walking holidays, the last was the pilgrim trail in Spain.