What’s the Difference Between a Stalactite and a Stalagmite?


Well-meaning geologists ended up confusing plenty of folks when they named stalactites and stalagmites. Both of these similar-sounding structures—typically formed in limestone caves—are capable of stretching over 27 feet in length. But what's the difference between them, and how do such strange ornaments grow in the first place?

Let’s clear up the terminology. Here’s a helpful (and widely-used) phrase you can use to sort out which is which: “Stalactites hold tight to the ceiling and stalagmites might touch the ceiling.” In other words, stalactites form on the roofs of caves and dangle downward like rocky icicles. Stalagmites, in contrast, are based on the floor and stretch upwards, only occasionally coming into contact with the overhanging ceiling.

An alternate memorization method goes as follows: “stalactite” is spelled with a “t,” as in “top.” “Stalagmite” uses the letter “g," as in “ground.”

According to the Oxford English Dictionary, these two terms descended from the Greek word stalaktos, which means “to drip." This is because trickling rainwater is responsible for the conical objects’ formation. When rain seeps through limestone, the water extracts carbon dioxide gas from the rock. What results is a weak carbonic acid that penetrates the stone and deposits a patch of calcite on the caves’ roof. As the water continues dripping, more and more calcite is added to the spot, eventually producing a lengthy stalactite.

But what about stalagmites? There’s a reason these are generally found directly underneath stalactites—all that dripping water has to land somewhere, after all. When a drop finally hits the cave floor, it deposits even more calcite there, this time in an unassuming mound. The liquid keeps dripping off the tip of a stalactite and the lump keeps rising, leaving us with a surging stalagmite. To call this process gradual would be a gross understatement. In limestone caverns, the usual growth rate is under 10 centimeters per millennium. 

It’s also worth noting that both stalagmites and stalactites belong to a larger geological group known as “speleothems." This is an extensive family of differently-shaped mineral formations that also includes globular “cave popcorn” and stunningly-beautiful “flowstones." Additionally, lava is occasionally involved in stalactite creation, leading to some strange-looking results. 

Why You Should Never Take Your Shoes Off On an Airplane

What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
20th Century Fox Home Entertainment

A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

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

Big Questions
Where Should You Place the Apostrophe in President's Day?

Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.

Wikimedia Commons // Public Domain

Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

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