Sleeping Giant
      Right now, an eruption is brewing in Yellowstone National Park. Sometime during the next two hours, the most famous geyser. Old Faithful, will begin gurgling boiling water and steam._____1_____
      Old Faithful is not only a spectacular sight; it’s also a constant remainder that Yellowstone sits on one of the largest volcanoes in the world. If you’ve never heard of Yellowstone’s volcano, you’re not alone._____ 2_____ yet it has erupted three times during the last million years. And one of those eruptions spewed enough volcanic ash and other debris to blanket half the United States.
      Yellowstone’s volcano is sometimes called a “supervolcano,” or extremely large and explosive caldera volcano._____3_____. This supervolcano formed over a hot spot, an extremely hot area in Earth’s mantle. John Valley, a volcano professors, said that as the crust moves across a hot spot, the hot spot melts a section of the plate moving over it,forming “one volcano after another.”
      The Yellowstone hot spot melts thick continental crust, which may cause catastrophic eruptions. According to experts the eruptions that created each of the three calderas in and around Yellowstone National Park were larger than any other volcanic eruption in recorded history. The most recent eruption, which happened 640,000 years ago, produced at least 1,000 cubic kilometers of ash and debris, which blanketed most of the western half of the United States._____4_____
Geological evidence shows Yellowstone has blown its stack every 700,000 years or so. “If nature were truly that regular and reliable, we would be due for another eruption soon,” said Valley. “However, these processes are subject to variability, so we don’t really know when the next eruption will happen.”
      _____5_____It is the volcanic energy that powers the geysers and hot springs, creates the mountains and canyons, and generates the unique ecosystems that support Yellowstone’s diverse wildlife.

A  Three calderas make up more than a third of Yellowstone National Park.
B  The first Yellowstone eruption, 2 million years ago, released more than double that amount of ash and debris.
C  The volcano is so inconspicuous (不显眼的) that few people know it exists.
D  Then, an enormous fountain will shoot high into the air.
E  While the active geologist processes at Yellowstone do pose some risk to the public, they also make it a unique treasure.
F  Yellowstone National Park attracts the interest of geologists the world over.

High Dive
      Cheryl Sterns aims to go boldly where no human has ever gone before in a balloon: 40 kilometers up into the atmosphere._____ 1_____No one has ever leapt from such a height or gone supersonic without an airplane or a spacecraft. Yet Sterns, an airline pilot, is not the only person who wants to be the first to accomplish those feats. Two other brave people, an Australian man and a Frenchman, are also planning to make similar leaps.
      _____2_____First, she’ll climb into a cabin hanging from a balloon the size of a football field2. Then balloon will take her high into the stratosphere—the layer of Earth’s atmosphere 12 to 50 kilometers above the planet. “The ascent will take two and a half to three hours,” said Sterns. “I’ll be wearing a fully pressurized, temperature-controlled space suit.”
At 40 kilometers, Sterns will be able to see the gentle curve of Earth and the blackness of space over head. Then she’ll unclip herself from the cabin and dive headfirst, like a bullet, into the atmosphere._____ 3_____
      For high dive, astronaut escape suits are a key to success. Current pilot and astronaut escape suite are guaranteed only a maximum altitude of 21 kilometers. Del Rosso, a NASA engineer of spacesuits and life-support systems, said the suit designed for Stern’s jump could serve as a model for the lethal environment of higher climbs._____ 4_____The first hazard is oxygen-deficient air. Any person without an additional oxygen supply at 40 kilometers would die within three to five seconds. The second hazard is low atmospheric pressure. Atmospheric pressure is much lower at high altitudes than it is at sea level. The low atmospheric pressure of the upper stratosphere causes the gases in body fluids to fizz out of solution like soda bubbles._____ 5_____Other hazards include temperatures as low as –55 degrees Celsius, flying debris, and solar radiation.
      For Sterns to survive, her spacesuit will have to protect her from all of these hazards. “A spacesuit is like a one-person spaceship,” Del Rosso explained. “You have to take everything you need in a package that’s light enough, mobile enough, and tough enough to do the job. You can’t exist without it.”

A  It will handle several major hazards.
B  Escape suits are tough enough to stand the atmospheric pressure of the upper stratosphere.
C  From there, she’ll take a death-defying leap back to Earth at supersonic speed.
D  “In 30 seconds, I’ll be going Mach (马赫) speed,” said Sterns.
E  How will Sterns make her giant jump?
F  In short, blood boils.