What Causes Sinkholes?

Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

Why Do We Wear Costumes on Halloween?

nito100/iStock via Getty Images
nito100/iStock via Getty Images

There’s no one explanation for how Halloween costumes originated. Much like the holiday itself, the practice of dressing up is the result of a hodgepodge of traditions from around the world.

Many historians suspect that the tradition has some basis in the Celtic festival of Samhain (also called Calan Gaeaf in Wales). Celebrated between the autumn equinox and the winter solstice, Samhain marks the official start of winter—known to the Celts as the “dark season.” During Samhain, “the world of the gods was believed to be made visible to humankind,” according to the Encyclopedia Britannica.

That wasn’t a comfort to the ancient Celts, who believed their deities were prone to playing tricks on human worshippers. Many festival participants disguised themselves as animals or beasts, hoping to hide from malevolent spirits who might bring them misfortune.

Move forward a few centuries and the modern-day practice of dressing up and trick-or-treating has its roots in the European custom of “mumming and guising.” Mummers would dress up in costumes, often woven from straw, and perform plays and songs for neighbors in exchange for food. Scottish and Irish immigrants brought that tradition to North America, where it later morphed into what we now know as trick-or-treating.

Halloween costumes didn’t experience their true heyday until the mid-1900s, though. For that, you can thank New York City entrepreneurs Ben and Nat Cooper, who started a company producing pop culture-themed costumes at a low cost. Ben Cooper, Inc., found a niche in helping kids become the characters they admired from television and comic books, often purchasing merchandising rights before said characters ever became popular. Due in no small part to the Cooper family’s innovation, Halloween costumes became an accessible and even necessary part of holiday festivities.

Today, Halloween costumes are big business. The National Retail Federation estimates that Americans will spend about $3.2 billion on costumes this year (of that, about half a billion will go to costuming pets). You have to wonder what the ancient Celts would have thought about today’s Halloween costumes.

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What's the Difference Between a College and a University?

Chinnapong/iStock via Getty Images
Chinnapong/iStock via Getty Images

Going off to college is a milestone in any young adult’s life. The phrase itself conjures up images of newfound independence, exposure to new perspectives, knowledge, and possibly even one or more sips of alcohol.

In America, however, few people use the phrase “going off to university,” or “headed to university,” even if they are indeed about to set off for, say, Harvard University. Why did college become the predominant term for postsecondary education? And is there any difference between the two institutions?

While university appears to be the older of the two terms, dating as far back as the 13th century, schools and students in North America have embraced college to describe most places of higher learning. There is no rigid definition of the words, but there are some general attributes for each. A college is typically a four-year school that offers undergraduate degrees like an associate or a bachelor’s. (Community colleges are often two-year schools.) They don’t typically offer master’s or doctorates, and the size of their student body is typically the smaller of the two.

Universities, on the other hand, tend to offer both undergraduate and graduate programs leading to advanced degrees for a larger group of students. They can also be comprised of several schools—referred to as colleges—under their umbrella. A university could offer both a school of arts and sciences and a school of business. The University of Michigan has a College of Engineering, for example.

While many of these traits are common, they’re not guaranteed. Some colleges can be bigger than universities, some might offer master’s degrees, and so on. To complicate matters further, an institution that fits the criteria of a university might choose to call itself a college. Both Dartmouth College and Boston College qualify as universities but use the college label owing to tradition. Schools may begin as colleges, grow into universities, but retain the original name.

People tend to think of a university as being more prestigious or harder to get into, but there are too many variables to make that determination at a glance. Some colleges might ask more of applicants than universities. Some universities might be smaller than certain colleges. Either one can be public or private.

Things get a little more convoluted abroad. In the UK, students go off to university (or uni) instead of college. The British version of college is typically a two-year program where students either focus on learning one particular skill set (much like a vocational school) or use the time to prepare for exams so that they can advance to university. Language matters, too; in Spanish, colegio usually refers to high school.

While the terms aren’t strictly interchangeable, there is enough of a difference between the two to try and make the distinction. Keep in mind that some states, like New Jersey, have rules about how institutions label themselves. There, a university has to have at least three fields of graduate study leading to advanced degrees.

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