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How Can We Tell When a Volcano is Dormant or Extinct?

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When a volcano makes the news for erupting, you’ll often hear mention of other kinds of volcanoes that are dormant or extinct. But what do those terms mean, exactly, and how do scientists figure that out?

First, a little bit about how volcanoes work: Magma collects in reservoirs beneath the earth’s surface, and as it accumulates, pressure in the chamber increases; if it gets high enough, the rocks over it will break, and an eruption will ensue. The silica content of the magma determines what kind of volcano you’ll have. Low silica magma makes shield volcanoes, like Kīlauea on Hawaii’s big island, and cinder cones, like Mexico’s Paricutín, which have lava that flows easily, like molasses. High silica magma creates stratovolcanoes, like Mount St. Helens in Washington, and calderas like the one under Yellowstone National Park, which have lava that is more viscous and flows like taffy.

The definitions of what constitutes dormant and extinct volcanoes aren’t exact, and can differ depending on the volcano or the scientist. Typically, says Jim Webster, Curator of Department of Earth and Planetary Sciences, Division of Physical Sciences at the American Museum of Natural History, scientists will look at recent history and the geologic record. If a volcano has erupted since the last Ice Age—in the last 10,000 years or so—and is still showing activity like lava and ash flows or gas emissions, it’s considered to be active. If a volcano hasn’t erupted in the last 10,000 years, but scientists think it will erupt again, it’s considered dormant. “If it has been more than 10 thousand years [since the volcano has erupted],” and the volcano is cut off from its magma supply, “it’s considered to be extinct,” Webster says.

Another indicator is seismicity—or lack thereof. “Often times the magma bodies, or chambers—the source that feeds eruptions—are three to eight miles below the surface, and you can monitor seismic behavior there,” Webster says. “If there’s a repeated concentration of seismic activity immediately below the opening, there’s probably hot, active magma down there. If that goes quiet and dormant, and its just background kind of seismic activity—shifting of the rock or weathering, how the planet’s always kind of creaking and moving—for an extended period, perhaps years, that would indicate that, if there’s magma there, it’s not moving. It’s not working toward surface, it’s not generating pressure to try to break the rocks, and perhaps the system is going extinct.”

But even a volcano that’s been deemed extinct could erupt again. “Magma bodies can cool and crystallize below the surface,” Webster says. “The magma may find a fracture and move off someplace else, and come up miles away or a long distance away.”

Because of this, scientists keep tabs on volcanoes whether they’re considered active, dormant, or extinct. “They do thermal monitoring, just to see if there’s heat,” Webster says. They also place tilt monitors on the volcano, which notify scientists if the ground starts to swell—a sign that an eruption could be imminent. (Before Mount St. Helens erupted in 1980, there was “a huge bulge visible to the eye,” Webster says.) And they also use instruments in space to monitor how things are going on the ground: “InSAR,” Webster says, “is a special type of radar that’s done from satellites. It can detect centimeter motions from space, on a land surface.”

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

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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Big Questions
Why Do Baseball Managers Wear Uniforms?
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Basketball and hockey coaches wear business suits on the sidelines. Football coaches wear team-branded shirts and jackets and often ill-fitting pleated khakis. Why are baseball managers the only guys who wear the same outfit as their players?

According to John Thorn, the official historian of Major League Baseball since 2011, it goes back to the earliest days of the game. Back then, the person known as the manager was the business manager: the guy who kept the books in order and the road trips on schedule. Meanwhile, the guy we call the manager today, the one who arranges the roster and decides when to pull a pitcher, was known as the captain. In addition to managing the team on the field, he was usually also on the team as a player. For many years, the “manager” wore a player’s uniform simply because he was a player. There were also a few captains who didn’t play for the team and stuck to making decisions in the dugout, and they usually wore suits.

With the passing of time, it became less common for the captain to play, and on most teams they took on strictly managerial roles. Instead of suits proliferating throughout America’s dugouts, though, non-playing captains largely hung on to the tradition of wearing a player's uniform. By the early to mid 20th century, wearing the uniform was the norm for managers, with a few notable exceptions. The Philadelphia Athletics’s Connie Mack and the Brooklyn Dodgers’s Burt Shotton continued to wear suits and ties to games long after it fell out of favor (though Shotton sometimes liked to layer a team jacket on top of his street clothes). Once those two retired, it’s been uniforms as far as the eye can see.

The adherence to the uniform among managers in the second half of the 20th century leads some people to think that MLB mandates it, but a look through the official major league rules [PDF] doesn’t turn up much on a manager’s dress. Rule 1.11(a) (1) says that “All players on a team shall wear uniforms identical in color, trim and style, and all players’ uniforms shall include minimal six-inch numbers on their backs" and rule 2.00 states that a coach is a "team member in uniform appointed by the manager to perform such duties as the manager may designate, such as but not limited to acting as base coach."

While Rule 2.00 gives a rundown of the manager’s role and some rules that apply to them, it doesn’t specify that they’re uniformed. Further down, Rule 3.15 says that "No person shall be allowed on the playing field during a game except players and coaches in uniform, managers, news photographers authorized by the home team, umpires, officers of the law in uniform and watchmen or other employees of the home club." Again, nothing about the managers being uniformed.

All that said, Rule 2.00 defines the bench or dugout as “the seating facilities reserved for players, substitutes and other team members in uniform when they are not actively engaged on the playing field," and makes no exceptions for managers or anyone else. While the managers’ duds are never addressed anywhere else, this definition does seem to necessitate, in a roundabout way, that managers wear a uniform—at least if they want to have access to the dugout. And, really, where else would they sit?

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