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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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What’s the Difference Between Prison and Jail?
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Many people use the terms jail and prison interchangeably, and while both terms refer to areas where people are held, there's a substantial difference between the two methods of incarceration. Where a person who is accused of a crime is held, and for how long, is a factor in determining the difference between the two—and whether a person is held in a jail or a prison is largely determined by the severity of the crime they have committed.

A jail (or, for our British friends, a gaol) refers to a small, temporary holding facility—run by local governments and supervised by county sheriff departments—that is designed to detain recently arrested people who have committed a minor offense or misdemeanor. A person can also be held in jail for an extended period of time if the sentence for their offense is less than a year. There are currently 3163 local jail facilities in the United States.

A jail is different from the similarly temporary “lockup”—sort of like “pre-jail”—which is located in local police departments and holds offenders unable to post bail, people arrested for public drunkenness who are kept until they are sober, or, most importantly, offenders waiting to be processed into the jail system.

A prison, on the other hand, is usually a large state- or federal-run facility meant to house people convicted of a serious crime or felony, and whose sentences for those crimes surpass 365 days. A prison could also be called a “penitentiary,” among other names.

To be put in a state prison, a person must be convicted of breaking a state law. To be put in a federal prison, a person must be convicted of breaking federal law. Basic amenities in a prison are more extensive than in a jail because, obviously, an inmate is likely to spend more than a year of his or her life confined inside a prison. As of 2012, there were 4575 operating prisons in the U.S.—the most in the world. The country with the second highest number of operating prisons is Russia, which has just 1029 facilities.

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What Do Morticians Do With the Blood They Take Out of Dead Bodies?
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Zoe-Anne Barcellos:

The blood goes down the sink drain, into the sewer system.

I am not a mortician, but I work for a medical examiner/coroner. During an autopsy, most blood is drained from the decedent. This is not on purpose, but a result of gravity. Later a mortician may or may not embalm, depending on the wishes of the family.

Autopsies are done on a table that has a drain at one end; this drain is placed over a sink—a regular sink, with a garbage disposal in it. The blood and bodily fluids just drain down the table, into the sink, and down the drain. This goes into the sewer, like every other sink and toilet, and (usually) goes to a water treatment plant.

You may be thinking that this is biohazardous waste and needs to be treated differently. [If] we can’t put oil, or chemicals (like formalin) down the drains due to regulations, why is blood not treated similarly? I would assume because it is effectively handled by the water treatment plants. If it wasn’t, I am sure the regulations would be changed.

Now any items that are soiled with blood—those cannot be thrown away in the regular trash. Most clothing worn by the decedent is either retained for evidence or released with the decedent to the funeral home—even if they were bloody.

But any gauze, medical tubing, papers, etc. that have blood or bodily fluids on them must be thrown away into a biohazardous trash. These are lined with bright red trash liners, and these are placed in a specially marked box and taped closed. These boxes are stacked up in the garage until they are picked up by a specialty garbage company. I am not sure, but I am pretty sure they are incinerated.

Additionally anything sharp or pointy—like needles, scalpels, etc.—must go into a rigid “sharps” container. When they are 2/3 full we just toss these into one of the biotrash containers.

The biotrash is treated differently, as, if it went to a landfill, then the blood (and therefore the bloodborne pathogens like Hepatitis and HIV) could be exposed to people or animals. Rain could wash it into untreated water systems.

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

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