Kaapvaal Craton South Africa

Cratons Africa

The Archean Kaapvaal craton of southern Africa contains some of the world's oldest and most intensely studied Archean rocks, yet nearly 86 percent of the craton is covered by younger rocks. The craton covers approximately 363,000 square miles (585,000 km2) near the southern tip of the African continent. The craton is bordered on the north by the highgrade Limpopo mobile belt, initially formed when the Kaapvaal and Zimbabwe cratons collided at 2.6 billion years ago. On its southern and western...

History of Levee Building on the Mississippi River

Mississippi River Widening 100 Miles

The Mississippi River is the longest river in the world and encompasses the third-largest watershed, draining 41 percent of the continental United States including an area of 1,245,000 square miles (3,224,550 km2). The river transports 230 million tons of sediment, including the sixth-largest silt load in the world. Before the Europeans came and began altering the river, this silt used to cover the flood-plains with this fertile material during the semiannual floods and carry more downriver to...

Examples of landslide disasters

Mass wasting is one of the most costly of natural hazards, with the slow downslope creep of material causing billions of dollars in damage to properties every year in the United States. Earth movements do not kill many people in most years, but occasionally massive landslides take thousands or even hundreds of thousands of lives. Mass wasting is becoming more of a hazard in the United States as people move in great numbers from the plains into mountainous areas as population increases. This...

Supercontinents and Climate

Cretaceous Plates Changing

The motion of the tectonic plates periodically causes most of the continental landmasses of the planet to collide with each other, forming giant continents known as supercontinents. For much of the past several billion years, these supercontinents have alternately formed and broken up in a process called the supercontinent cycle. The last supercontinent was known as Pangaea, which broke up about 160 million years ago to form the present-day plates on the planet. Before that the previous...

The Worlds Diminishing Freshwater Supply

Freshwater Floods

On a global scale only about half of the world's population has a connection to a piped-water supply in the home, whereas 30 percent rely on wells or local village pipes, and about 20 percent have no access at all to clean water. World population is expected to grow by another 50 percent (another 3-4 A levee on the Mississippi River being overtopped, with water flooding farmlands in Winfield, Missouri, during Midwest floods of summer 2008 (T. Kusky) billion people) in the next 50 years, so huge...

Thermohaline Circulation and Climate

Variations in formation and circulation of ocean water may cause some of the thousands of years to decadal scale variations in climate. Cold water forms in the Arctic and Weddell seas. This cold, salty water is denser than other water in the ocean, so it sinks to the bottom and gets ponded behind seafloor topographic ridges, periodically spilling over into other parts of the oceans. The formation and redistribution of North Atlantic cold bottom water accounts for about 30 percent of the solar...

Types Of Satellite Imagery

Satellite imagery forms one of the basic tools for remote sensing. The types of satellite images available to the geologist, environmental scientist, and others are expanding rapidly, and only the most common in use are discussed here. The Earth Resources Technology Satellite (ERTS-1), the first unmanned digital imaging satellite, was launched on July 23, 1972. Four other satellites from the same series, later named Landsat, were launched at intervals of a few years. The Landsat spacecraft...

Shaanxi China January 23 1556

The deadliest earthquake and mass-wasting event on record occurred in 1556 in the central Chinese province of shaanxi. Most of the 830,000 deaths from this earthquake resulted from landslides and the collapse of homes built into loess, a deposit of wind-blown dust that covers much of central China. The loess represents the fine-grained soil eroded from the Gobi desert to the north and west and deposited by wind on the great loess plateau of central China. Thus, this disaster was triggered by an...

The Worlds Oldest Ophiolite

Early Earth Evolution Sketch

Prior to 2001, no complete Phanerozoic-like ophiol-ite sequences had been recognized from Archean rock sequences around the world, leading some workers to the conclusion that no Archean ophiolites or oceanic crustal fragments are preserved. These ideas were challenged by the discovery of a complete 2.5 billion-year-old ophiolite sequence in the North China craton. This remarkable rock sequence includes chert and pillow lava, a sheeted dike complex, gabbro and layered gabbro, cumulate ultramafic...

Scientific DiscovERIES

Kent Condie

Tycho Brahe grew up in a scientific era in which Aristotelian ideas that the universe was unchanging followed the principle of celestial immutability. While based at his observatory at Herrevad, Brahe made many observations on the planets and stars. On November 11, 1572, he made a discovery that changed the thinking about the universe. He observed a very bright star that appeared in the constellation Cassiopeia and showed that no star had been visible in that location before. At first other...

Thera Greece 3650 years before Present

Location Map Thera

One of the greatest volcanic eruptions in recorded history occurred approximately 3,650 years ago in the eastern Mediterranean region, then the cradle of civilization. Santorini is a small, elliptically shaped archipelago of islands, approximately 10 miles (16 km) across, located about 70 miles (110 km) north of the island of Crete. The islands are dark and ominous in stark contrast to the white limestone of the Greek islands, and they form ragged, 1,300-foot (390-m) peaks that seem to point up...

Characteristics Of Electromagnetic Radiation

Radiation from different wavelengths in the electromagnetic spectrum has very different characteristics and uses. Radio waves have wavelengths ranging from one millimeter to hundreds of meters and frequencies of about 3 Hz to 300 GHz. They are commonly used by people to transmit data for television, mobile phones, wireless internet connections, and many other applications. The technology to encode radio waves with data is complex but involves changing the amplitude and frequency and phase...

Desert drainage systems

Most streams in deserts evaporate before they reach the sea. Most are dry for long periods of time and subject to flash floods during brief but intense rains. These flash floods transport most of the sediment in deserts and form fan-shaped deposits of sand, gravel, and boulders found at the bases of many mountains in desert regions. These flash floods also erode deep, steep-walled canyons through the upstream mountain regions, which is the source of the boulders and cobbles found on the...