Get a grip! Junior climbing champ Scott Cory built his iron grip clinging to rock walls. Find out why certain kinds of rock make his favorite climbing spots so challenging.

Scott Cory, 13, is tough. The 8th grader from Brentwood, California, recently took only 14 hours to climb Half Dome, Yosemite National Park's famous 2,000-foot-high wall. The massive rock typically takes skilled climbers three days to scale. "Climbing big walls is like doing pull-ups for 14 hours," he says.

But that's not the hardest part. As he scurries up a smooth rock, Scott must balance his weight on holds, climber-speak for a rock's cracks and ledges--sometimes no thicker than a pencil. He carefully maneuvers between them by crushing his shoes, hands, and body into the rock. With each new grip, he inches up against gravity (force that pulls objects toward Earth).

Large holds are easier to grip and balance on, while small holds spaced far apart create challenging technical climbs. "Rock climbers try to get as much friction (force that resists movement) as they can between their hands, feet, and the wall," says Steven Gubser, a physics professor at Princeton University who has also climbed since he was in college. "Bigwall climbers make the most of every tiny feature in a rock's surface." The number and size of these lifesaving features depends on the type of rock a climber is on. Turn the page to check out how the rocks at Scott Cory's favorite climbing routes, or paths, make for gripping climbs.

ROUTE: HALF DOME

WHERE: Yosemite National Park, California

ROCK TYPE: Granite

BIGGEST CHALLENGE: Slabs are smooth, so it's hard to find holds.

On the climber's scale, 5.1 marks an easy route, while 5.14 is reserved for Spiderman and elite climbers. Half Dome ranks at 5.8. What makes it tricky? The smooth granite surface. "Sometimes the holds blend in with the rock, so you can't see them," says Scott. "I have to feel for the holds."

Granite, an igneous rock (see diagram, page 13), forms when magma (melted rock) deep underground cools and solidifies. The jolting movement of Earth's upper crust forced the rock above ground. Then millions of years of weathering (wearing away by wind and water) chiseled the rock's surface. Glaciers that swept through during the last ice age polished Yosemite's granite even more, forming smooth slabs.

Luckily for climbers, granite also easily forms cracks. "When the big molten blobs of rock cooled, they shrank, and that caused the solid rock to fracture," says Thomas Kalakay, a geologist at Vanderbilt University. Climbers rely on these vertical cracks to reach the top. They cram fists and toes into slivers in the rock in a technique called jamming "You have to put a lot more energy and muscle into it," says Scott.

ROUTE: NOTHING SHOCKING

WHERE: Red Rock Canyon, Nevada

ROCK TYPE: Sandstone

BIGGEST CHALLENGE: A softer type of rock, sandstone crumbles easily.

Few climbers tackle a wall without proper protection: a helmet, ropes, anchors, and a partner. And for good reason: "I fall a lot--just not to the ground," says Scott. "Without the ropes, I'd die." In sport climbing, park officials have already drilled permanent steel anchors, or bolts, into the rocks. As climbers scale a sheer vertical, they use metal hooks, called carabiners, to clip their ropes to the bolts. If climbers slip, their partner, who's watching below, pulls tightly on the rope, which catches in the hook. Climbers only fall as far as the last spot they clipped in to.

Sandstone's unique geology challenges a climber's safety. That's because the reddish-tinted rock is sedimentary. It formed when sediment, like rock particles at the bottom of a river, piled on top of one another and cemented together. Red Rock's sandstone cliffs are made of layers of quartz grains (sand) blown off desert dunes that covered the area more than 180 million years ago. Over time the layers were buried, glued together by pressure, and weathered, to produce gut-wrenching 5.13 climbs.

The problem: "The grains in the sandstone aren't held together super well, so the rock may fall apart when you put force on it," says Kalakay. On over-traveled routes, weakened holds might crumble beneath your fingers. "And bolts wiggle out over time," he says. The same is true for many metamorphic rocks (rocks formed when igneous, sedimentary, or other metamorphic rocks are changed by heat and pressure), such as slate. Its layers are even finer, and large chunks can split off under pressure.

ROUTE: CORROSION CAVE

WHERE: Mt. Charleston, Nevada

ROCK TYPE: Limestone

BIGGEST CHALLENGE: Forms steep, overhanging cliffs that can leave a climber dangling.

Limestone is a climber's dream rock! While limestone is a sedimentary rock (like sandstone), its layers are made of calcium carbonate (calcite), a mineral that can dissolve in water. Many caves form from water trickling through limestone over millions of years. "In a shorter period of time, limestone makes mini caves and pockets in the rock that you can stick your hands and fingers in," says Kalakay.

Sometimes the bottom of a limestone face dissolves faster than the top does. That creates massive rock overhangs, ledges that jut horizontally front a wall. Climbers navigate these ledges mostly by hanging from their hands. "If the climber is hanging by her arms, then the force on the hands alone must compensate for the force of gravity," says Steve Giddings, a climber and physics professor at the University of California at Santa Barbara.

That's one reason limestone is rated for experienced climbers only: Corrosion cave routes rank between 5.11 and 5.14. And for young climbers like Scott, it's especially hard. No matter how many push-ups he does, he doesn't yet have the rippling muscles of his older climbing buddies. But that won't keep this wall rat off tough climbs. Says Scott: "You just have to try hard and keep on trying."

YOSEMITE NATIONAL PARK, CA

Yosemite's smooth granite slabs are the most popular place to climb in the U.S.

ROCK STAR

Scott Cory is the youngest person to climb Half Dome in less than a day.

MT. CHARLESTON, NV

Steep limestone cliffs force this climber to hang from his hands.

MAP IT!

Shown here are five other popular climbing spots in the U.S. Do some research: Which of the three major rock types can be found in each park?

RED ROCK CANYON, NV

The park's sandstone walls used to be at the bottom of an ocean 600 million years ago.

THE ROCK CYCLE

There's no starting point to this cycle, which has been going on for millions of years. Rocks form deep underground and get pushed to the surface as Earth's crust moves or volcanoes erupt. Wind and water wear away at the rocks.

IGNEOUS ROCK

Formed when metamorphic rocks melt to form magma (melted rock), which then cools underground or erupts and cools on Earth's surface.

METAMORPHIC ROCK

Formed when metamorphism (heat and pressure) changes sedimentary, igneous, or other metamorphic rocks.

SEDIMENTARY ROCK

Formed when layers of sediment are squeezed and cemented together.

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Did You Know?

* "Ordinarily, friction wouldn't permit you to climb a slope more than 45 degrees," says physicist Steven Gubser. You can demonstrate this by placing a penny on a piece of cardboard. Slowly tilt the cardboard from one end. The penny will stay on the cardboard due to friction, but it will start to slip when the angle of the board goes above 45 degrees. "But a good rock climber can climb without any hand holds up a pretty steep face--maybe 60 degrees," he says. That's because they balance on holes and cracks in the surface of the rock. And that decreases the angle of the surface they're "standing on." Climbers also wear rubber shoes that increase friction.

* Besides sport climbing--featured in the story--there are two other major types of rock climbing: traditional and bouldering. Traditional climbers place their own bolts, called protection, in the rock as they climb. And bouldering is climbing low-hanging rock, not much higher than 10 feet, without ropes. Climbers have a spotter and pads to catch a fall.

Cross-Curricular Connection:

Geography/History: As a class, research your county's geology and create a map of significant rock formations--be sure to include a description of the rock and the processes that formed it. What historical landmarks, industries, or stories are related to the rocks? For example: Was the county courthouse built from stones mined from at local quarry?

Resources

For an overview of the tools and techniques involved in rock climbing, visit, travel.howstuffworks.com/rock-climbing.htm

This Web site, popular among climbers, has a wealth of information on the sport, including stats on the most-visited climbing areas and stunning photos: www.rockclimbing.com

This book is a kid-friendly guide to geology and earth-building processes: The Visual Dictionary of the Earth, edited by. Martyn Bramwell, Dorling Kindersley, 1993.

For a complete, printable diagram of the rock cycle and sample exam questions see: regentsprep.org/Regents/earthsci/rockcycle.htm