This special-edition episode examines what happened in the 1906 San Francisco earthquake and its effect on San Francisco and looks at the destruction if it were to happen again today.

The possibility of a tornado hitting downtown Chicago is the scenario. Included is an examination of the 1967 twister that hit the suburb of Oak Lawn.

It has been a century since the infamous 1906 San Francisco earthquake and Californians live with the knowledge that it's only a matter of time before they're hit again. Los Angeles is the second most populous city in America. If an earthquake hit directly beneath downtown LA, scientists believe that tens of thousands would be killed. Just how would the city respond to a 7.5 magnitude quake? Take a look at how well the emergency responders could cope. A CGI worst-case scenario will show the incredible damage and destruction that would cripple one of the most important cities in the world.

Mount Rainier is a ticking time bomb that could dwarf the 1980 eruption of Mount St. Helens, sending massive lahars and mudslides toward the Seattle-Tacoma metropolitan area.

Anthrax is the most feared of all the biological weapons--spores entering the body through the lungs are lethal. In 2001, a simple letter, sent through the US mail, paralyzed a nation, when anthrax spores were found inside. Experts predict that anthrax released over a populated area would result in unprecedented loss of life--a few pounds of anthrax released under the right conditions could kill hundreds of thousands of people. Will anthrax be used to create a worldwide disaster?

The 1883 eruption of Krakatoa was one of the deadliest natural disasters in recorded history, claiming over 36,000 lives by the tsunamis it triggered. Another volcanic eruption at Krakatoa, now called Anak Krakatau (meaning "Child of Krakatoa" in Indonesian), could spell curtains for Indonesia.

The U.S. Department of Energy and the Nuclear Regulatory Commission plan to transport 77,000 tons of nuclear waste to a permanent storage facility 950 feet below Nevada's Yucca Mountain. If the plan goes through, much of the cargo will travel through Las Vegas, making an accident there a very disturbing possibility. If history has taught us anything, it's that transporting dangerous goods can sometimes have catastrophic results. Take a look at the potential disaster that such a rail accident would have in Las Vegas.

How a major tornado would impact Dallas is examined by studying the effect of a twister that struck Oklahoma City on May 4, 1999, killing 43 people and causing $1 billion in damage.

A Category 3 hurricane hitting New York City is the scenario. Included: a history of hurricanes in the Northeast; and the origins of such storms.

Since commercial aviation truly began in the 1930s, the romance of air travel has been marred by the tragedy of crashes. Unless significant changes continue to be made in airport infrastructure, aviation technology, and professional training, any American airport could be the site of the next Mega Disaster.

Modern dams are marvels of engineering but after decades of neglect the U.S. infrastructure is in crisis and by 2020, 85% of U.S. dams may be near their breaking point. When the South Fork Dam near Johnstown, Pennsylvania gave way in a storm in 1889, killing 2200 people, it was the worst disaster in U.S. history. Today, with millions of Americans living nearby massive dams, the result of a failure could be catastrophic.

In 6,000 BC, 8,000 years before the 2004 Indian Ocean tsunami, a paleotsunami whose waves reach taller than the Statue of Liberty allegedly was generated by a landslide from Mount Etna and ravaged the coasts of the Mediterranean Sea, devastating ancient villages and killing untold numbers. A team of scientists pieces together evidence of this megatsunami and reveals the face of this ancient tsunami for the first time. 3-D computer generated animation recreates the massive waves that may have changed the course of history.

The largest volcanic eruption of the past two million years occurred on the Indonesian island of Sumatra some 75,000 years ago. The impact from the supervolcano Mount Toba decimated the local habitat, but gas, ash and debris from Toba made their way around the planet and formed a shield in the atmosphere that deflected the sun's warming rays. Temperatures plummeted and the planet was thrown into a volcanic winter and may have even pushed the planet into an ice age. 3-D computer animation will recreate the storm and unveil how this one volcano could have brought humanity to the edge of extinction.

Cumbre Vieja, a volcano on the island of La Palma in the Canary Islands, off the northwestern coast of Africa, may potentially collapse in the future. If it does, a massive tsunami will be headed right for the East coast of the United States, threatening major cities like New York, Boston, Baltimore, and Miami.

Yellowstone National Park lies on top of a magma chamber that is 35-miles wide, waiting to erupt. (For further information, see Yellowstone Caldera.)

The possible effects of extreme climate changes around the world in a short period of time are examined. Included: how drought altered the Mayan civilization.

Methane gas precipitates out of the Earth's crust but is easily diluted in the air and in the oceans. Yet, according to one scientist, certain oceanic conditions could trap the gas in regions with low water circulation and build up extreme pressure. Once these areas are disturbed, the gas would blow out of the ocean in powerful jets. If they ignited before diluting, the explosion could cause widespread devastation. The scientist also posits that a similar event caused the Permian extinction.

Could an alien infection cause an epidemic on earth? Some experts believe that spacecraft returning from Mars could bring back a harmful sample or comet dust falling into our atmosphere could cause pandemics. One astronomer believes that the 1918 flu pandemic, which killed between 50-100 million people, was one such outbreak and that another "infection" could decimate the world's population. Astrobiologists are now poised to bring Mars samples back to earth to examine them in a Bio 4 level safety lab. In a hypothetical future disaster scenario, track how comet dust would seed the earth with a virulent virus. Quarantine measures don't work and panic ensues.

About 8,000 years ago, rain squalls had global oceans surging. The oceans rose above all of the earth. When the flood was over the Mediterranean Sea had claimed a landmass twice the size of Ireland. This prehistoric mega-storm was the greatest natural disaster in human history. 3-D computer animation will recreate what this lethal flood may have looked like.

Around 65 million years ago, a massive asteroid crashed into Mexico's Yucatan Peninsula. Nearly 75% of all life on earth vanished. But could a single asteroid have been the lone killer? Theories about what happened after the impact have been speculated on by the entire scientific community. Ranging from global warming to lethal worldwide firestorms, ideas have been put forth, but none have been proven. Then in 1995 a new theory claimed that a powerful mega-storm known as a hypercane caused the extinction. The hypercane allegedly reaches 20 miles into the stratosphere and has wind speeds of up to 500 miles per hour. 3-D computer graphics will reveal how this storm could have brought down nearly all life on the planet.

The Thera volcanic eruption nearly 4000 years ago at the site of what is now Santorini. Greece, and the resulting tsunami are recalled. Also: speculation regarding another possible eruption.

Could the island nation of Great Britain have once been connected to Europe by land? Listen to a new theory and evidence which suggests that the English Channel was created by one of the largest floods ever. Did a violent storm re-shape the European continent? Might this happen again? Dramatic 3-D animations recreate what this prehistoric mega storm may have looked like and unravel the mystery behind the creation of England.