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What Is the Difference Between a Crevice and a Crevasse?

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The difference between a crevice and a crevasse is more than just a few letters. It’s the difference between geology and glaciology. While both terms come from the Anglo-French word crevace, to break, they mean two different things. Crevices are cracks or splits caused by a fracture of a rock, while a crevasse is a deep fracture in a glacier or ice sheet.

Crevasses in a glacier. Image Credit: G310ScottS via Wikimedia Commons // CC BY-SA 3.0

 
Crevasses form in the top layers of a moving glacier, usually because some parts of the massive body are moving at a different pace than the rest. If a glacier is moving over varied terrain (over mountains and down valleys), for instance, the glacier can stretch and fracture. The part of the glacier moving over a mountain will move more slowly, while the part that’s flowing down through the adjacent valley will gain speed. As the ice pulls apart at the stress points between those two portions of the ice, cracks form. Crevasses can also form when the glacier turns a corner, since the ice on the outside moves faster than the ice on the inside as it goes around a bend, or in open areas where ice begins to spread out horizontally (as it often does at its front end).

Often covered by snow, crevasses pose a great threat to mountaineers as they traverse the surface of a glacier: That snow can give way, leading to a steep fall. While the intense pressure at the bottom of a glacier typically squeezes a crevasse closed long before the crack reaches bedrock, the opening between the two parts of the ice can still reach as far as 100 feet down. As a safety precaution, climbers undergo crevasse rescue training in which they learn how to attach themselves to each other using a rope; should one of them fall into a crevasse, the other can pull them to safety on the ice.

A glacier may have more than one crevasse, and when they come together, they form a kind of free-floating column of glacial ice separate from the rest of the glacier. Called seracs, these pose yet another risk to climbers, because they can topple easily.

One big crevice (and many smaller ones). Image Credit: upyernoz via Wikimedia Commons // CC BY 2.0

 
Meanwhile, a crevice doesn’t always pose a threat. These are formed when brittle rocks crack under stress, and the two sides begin to pull apart (rather than sliding past each other). While you wouldn’t want to fall down a large one, they’re not always dangerous—they can be as small as a crack you’d see in the sidewalk or as deep as a canyon. These rock formations are not typically a threat to hikers because they're typically easy to see; in fact, they can often be a great help to rock climbers. The small ones are great for hand-holds or to attach bolts to, and larger crevices can be scaled. They’re also habitats: In western North America, there are dozens of bat species that use crevices as roosts [PDF].

If you're wondering in the middle of a conversation whether to use "crevice" or "crevasse," it's probably safer to go with crevice—unless you spend a lot of time talking about glaciers. While it's technically a geological term, the word crevice is used much more generally to describe cracks and gaps, whether in rock or in other materials. For instance, engineers use the word to describe the gap between two joined metals. Weeds might grow in the crevices of a sidewalk or between bricks. Colloquially, you could describe the gaps in your couch cushions where all your change accumulates as crevices.

In short, if it's not ice and you aren't making a glacier metaphor, it's a crevice.

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Big Questions
Where Did the Myth That Radiation Glows Green Come From?
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by C Stuart Hardwick

Probably from radium, which was widely used in self-luminous paint starting in 1908. When mixed with phosphorescent copper-doped zinc sulfide, radium emits a characteristic green glow:


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The use of radioluminescent paint was mostly phased out by the mid-1960s. Today, in applications where it is warranted (like spacecraft instrument dials and certain types of sensors, for example), the radiation source is tritium (radioactive hydrogen) or an isotope of promethium, either of which has a vastly shorter half life than radium.

In most consumer products, though, radioluminescence has been replaced by photoluminescence, phosphors that emit light of one frequency after absorbing photons of a difference frequency. Glow-in-the-dark items that recharge to full brightness after brief exposure to sunlight or a fluorescent light only to dim again over a couple of hours are photoluminescent, and contain no radiation.

An aside on aging radium: By now, most radium paint manufactured early in the 20th century has lost most of its glow, but it’s still radioactive. The isotope of radium used has a half life of 1200 years, but the chemical phosphor that makes it glow has broken down from the constant radiation—so if you have luminescent antiques that barely glow, you might want to have them tested with a Geiger counter and take appropriate precautions. The radiation emitted is completely harmless as long as you don’t ingest or inhale the radium—in which case it becomes a serious cancer risk. So as the tell-tale glow continues to fade, how will you prevent your ancient watch dial or whatever from deteriorating and contaminating your great, great grandchildren’s home, or ending up in a landfill and in the local water supply?

Even without the phosphor, pure radium emits enough alpha particles to excite nitrogen in the air, causing it to glow. The color isn’t green, through, but a pale blue similar to that of an electric arc.


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This glow (though not the color) entered the public consciousness through this early illustration of its appearance in Marie Curie’s lab, and became confused with the green glow of radium paints.

The myth is likely kept alive by the phenomenon of Cherenkov glow, which arises when a charged particle (such as an electron or proton) from submerged sources exceeds the local speed of light through the surrounding water.

So in reality, some radionuclides do glow (notably radium and actinium), but not as brightly or in the color people think. Plutonium doesn’t, no matter what Homer Simpson thinks, unless it’s Pu-238—which has such a short half life, it heats itself red hot.


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This post originally appeared on Quora. Click here to view.

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Big Questions
How Are Royal Babies Named?
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After much anticipation, England's royal family has finally received a tiny new addition. The birth of the Duke and Duchess of Cambridge's second son was confirmed by Kensington Palace on April 23, but the name of the royal newborn has yet to be announced. For the heir to the British throne and his wife, choosing a name for their third child—who is already fifth in line to the throne—likely won't be as easy as flipping through a baby name book; it's tradition for royals to select names that honor important figures from British history.

According to ABC WJLA, selecting three or four names is typical when naming a royal baby. Will and Kate followed this unwritten rule when naming their first child, George Alexander Louis, and their second, Charlotte Elizabeth Diana. Each name is an opportunity to pay homage to a different British royal who came before them. Some royal monikers have less savory connotations (Prince Harry's given name, Henry, is reminiscent of a certain wife-beheading monarch), but typically royal babies are named for people who held a significant and honorable spot in the family tree.

Because there's a limited pool of honorable monarchs from which to choose, placing bets on the royal baby name as the due date approaches has become a popular British pastime. One name that keeps cropping up this time around is James; the original King James ruled in the early 17th century, and it has been 330 years since a monarch named James wore the crown.

If the royal family does go with James for the first name of their youngest son, that still leaves at least a couple of slots to be filled. So far, the couple has stuck with three names each for their children, but there doesn't seem to be a limit; Edward VIII, who abdicated the throne to George VI in 1936, shouldered the full name of Edward Albert Christian George Andrew Patrick David.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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