Victoria Falls

The Victoria Falls constitutes one of the most spectacular Natural Wonders of the World. It is most commonly referred to as "Mosi-ao-Tunya" which means The Smoke that Thunders.

The Victoria Falls is located in the southern part of Africa on the Zambezi river between the countries of Zambia and Zimbabwe. It is attributed to as the world's largest sheet of falling water and it is one of the Seven Natural Wonders of the World. In the year 1855, David Livingstone, the Scottish missionary and explorer, is believed to have been the first European recorded to view the Victoria Falls. This waterfall is 1708 meters (5604 ft) in width and 108 meters (354 ft) in height, which is roughly twice the height of North America's Niagara Falls and over twice the width of its Horseshoe Falls. The falls are formed as the full width of the river plummets in a single vertical drop into a transverse chasm, carved by its waters along a fracture zone in the basalt plateau. The dept of the chasm varies from 80 meters (262.5 ft) at its western end to 108 meters (354.3 ft) in the center, and this is called the First Gorge. The only outlet to the First Gorge is a 110 meters (360.9 ft) wide gap about two-thirds of the way across the width of the falls from the western end, through which the whole volume of the river pours into the Victoria Falls gorges.

The falls are actually split into a number of separate waterfalls owing to the small islands dotted along the top of the Falls that interrupt the curtain of water. Boaruka Island near the western bank and Livingstone Island near the middle are the two important islands on the crest of the falls that are large enough to separate the curtain of water even at the full flood. The other islands that divide the curtain of water into separate parallel streams are: Devil's Cataract, Main Falls, Rainbow Falls and the Eastern Cataract. 

The river's annual flood season is from Feb to May with a peak in April. During this full flood season, the spray from the falls typically rises to a height of over 400 meters and sometimes even twice as height and is visible from upto 50 km away. So, during this time of the year, the falls cannot be seen on foot on the Zimbabwe side with clouds of spray rising height into the sky and drenching all tourists. But it is the best time to see "Moonbow" that forms in the spray, at the full moon, instead of the normal daylight rainbow. From May as the annual flood abates, the view of the falls gets better and most of the Victoria Falls can be seen. 

source: http://www.absoluteastronomy.com/topics/Victoria_Falls

Cotopaxi

Cotopaxi is the sight to behold. Towering above the neighboring Andean peaks in north-central Ecuador, South America, it is an almost perfectly symmetrical volcanic cone. Dominating the capital city of Quito skyline to the south, 19,348 feet in elevation, Cotopaxi is the second highest peak in the Ecuador and the highest continually active volcano in the world. Its flanks are largely covered by permanent fields of snow and ice. And it is the snow that presents the greatest peril when the volcano intermittently erupts. Cotopaxi means "Smooth Neck of the Moon" and the native people have worshiped the mountain for centuries.
Cotopaxi's shapely profile was a long time in the making, for it is actually composed of two volcanic structures, with the newer one superimposed on its ancient ancestor. The older volcano called Picacho, was formed long before any of the neighboring extinct volcanoes in this area of the Andes. Traces of its caldera (a giant crater like cavity formed when a volcano's top collapses in an explosion.) are still visible on Cotopaxi's flanks.

Cotopaxi is known as a Stratovolcano: built up with lava flows alternating with layers of ash and other volcanic materials that were exploded from its vent. But the most deadliest effects of its eruptions result from Lahars - gigantic avalanches of mud and meltwater that periodically come flooding down its flanks. The first recorded eruption of Cotopaxi was in 1533. Of the many that have occurred since then, the worst took place in 1877. The explosions were heard over a radius of more than 200 miles, clouds of ash and pumice completely darkened the midday sky and the accompanying lahars killed thousands of people. Evidence of that catastrophic flow can still be seen throughout much of the countryside of the Sierras. Though Cotopaxi remains active, it has been long since the last large eruption.

For more details, visit: http://galapagosonline.wordpress.com/2010/04/20/cotopaxi/

Wind Cave

Wind Cave, located in the rugged Black Hills of South Dakota is one of the world's longest and complex cave. It was named for its very strong air currents that pass in and out of its entrance. Changes in barometric pressure rises apparently trigger these eerie winds. When the atmospheric pressure rises outside the cave, wind rushes in; then when the outside air pressure drops, the air rushes out again.
Wind Cave is remarkable for its unrivaled displays of the delicate rock formation known as Boxwork - The nature's intricate art wonders!. Boxwork is found in small amounts in other caves, but perhaps in no other cave in the world is boxwork so well-formed and abundant as in Wind Cave. [Boxwork is made of thin blades of calcite that project from cave walls and ceilings, forming a honeycomb pattern.] When the limestone containing the cave was uplifted some 60 million years ago, it was broken up by networks of intersecting cracks. Over long periods of time, seeping water deposited veins of the mineral calcite in the cracks. Later, when the cave was formed, the enveloping limestone was eroded away, while the more resistant calcite in the cracks was left projecting from the ceilings and walls in fragile, beautifully intricate patterns.
The Wind Cave National Park has a number of unusual attractions above the ground as well, 28,295 acres of mixed-grass prairie, ponderosa pine forest, and associated wildlife are the main features of this park.

Torcal De Antequera

Torcal de Antequera is a limestone plateau in the mountains about 20 miles north of the port city of Malaga (Spain) on the mediterranean sea. All across the surface of the plateau, strangely eroded rock formations suggest the ruins of an ancient city. Oddly realistic sculptural forms and huge bastions that resemble ruins are seperated by labyrinths of alleys and rubble-strewn trenches.
No city ever rose on this site, however the ruins, in fact are the typical remnants of erosion in a limestone landscape. The limestone here, more than 2000 feet thick, was long ago broken up by vertical and horizontal fractures. At a time when the water table was high, the underground streams coursed through the fractures. The water dissolved the limestone and gradually enlarged the openings into a maze of galleries and chambers. Eventually the roofs of the tunnels caved in, forming the trenches - the streets and plazas of the ruined city. Ever since they were exposed, the rocky bastions that were left standing between the trenches have been attacked by wind and weather, which have gradually softened and reshaped their contours.
Meanwhile the water continues to work its way through the limestone that makes up the Plateau. Seeping through fractures at lower levels beneath the eroded surface, it is carving out new networks of channels, chasms, and caves. In time the ceilings may once again collapse, thereby revealing another, presently hidden underground landscape.