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A 6.8 earthquake hits near Kailua-Kona (Kona) on the Big Island. The pool never seems to lose any water. At 20 seconds, note the guys in the upper left corner, run out of their room, jump the wall and head to the beach.

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Last week's earthquake in western Montana was the strongest earthquake in the region in 60 years. An initial quake set off 10 smaller earthquakes, with people as far west as Seattle and as far north as Canada reporting feeling tremors. Even though this 5.8-magnitude quake was comparatively mild (just strong enough to move heavy furniture), scientists and residents near Yellowstone National Park were on edge: Was the legendary Yellowstone supervolcano about to explode?

First things first: Contrary to multiple fake news reports, the Yellowstone supervolcano remains dormant and quiet. But residents and scientists had every reason to fret, mostly because the Yellowstone supervolcano is actually a caldera.

A supervolcano is not just a big volcano. It occurs when magma continues to rise to the Earth's crust but is unable to escape, kind of the way pressure cookers trap steam. And just like the way a pressure cooker's top shoots up when it can't contain steam any more, a supervolcano explodes when it can't stifle the pressure of magma any more.

What makes the Yellowstone supervolcano especially dangerous is the fact that it's not actually a volcano but rather a caldera. Unlike the classic cone-shaped volcanos we normally model our childhood science projects on, calderas are actually inverse volcanoes, looking more like crater-shaped, sunken volcanos.

Supervolcanoes are especially devastating because of the river of lava that pours out in a short amount of time. For a normal volcano, this lava can be contained within the surrounding valley, but for a caldera, exit points collapse, flooding surrounding areas with lava and ash instead of being held within a valley of a traditional volcano.

Not all calderas are supervolcanoes, however - they can be, otherwise, benign and boring. But calderas that double as supervolcanoes are a deadly force. The wider the caldera, the heavier the flow of lava, and the more devastating the consequences.

For its part, the Yellowstone Caldera is roughly 30 miles long and 45 miles wide, which is considered pretty gigantic, mostly because it is the result of three eruptions. Researchers with the United States Geological Survey were able to trace out caldera boundaries by looking at the rock formations: The first caldera formed 2.1 million years ago and erupted 600 cubic miles worth of magma; the second caldera formed 1.3 million years ago with 67 cubic miles of magma; and the third formed 640,000 years ago with 240 cubic miles of magma.

Researchers consider the Yellowstone Caldera a supervolcano because of how big the eruptions are. Based on the volcanic exclusivity index, any volcano that produces 240 or more cubic miles of magma is considered a supervolcano. On top of the large eruptions, researchers also believe that the supervolcano could have magma stored in chambers more than 600 miles deep, with some scientists speculating that these chambers could run as deep as 1,800 miles.

Luckily, most of the pressure from the Yellowstone Caldera is released as hot water through geysers and hot springs, most famously through hot spurts of water like that of Old Faithful. The magma heats the groundwater above it, building pressure before shooting out hot water at an average height of 130 feet in the air.

The good thing about volcanos as big as the Yellowstone Caldera is that they don't erupt often. Researchers estimate that volcanos of that size only burst every 10,000 to 100,000 years, and they can see signs of possible eruptions in advance, such as an increase in earthquakes and changes in the land formations. And as of now, researchers don't see any imminent signs of a super-eruption anytime soon.

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Yellowstone's Supervolcano Is Especially Dangerous Because of Its Shape

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Last week's earthquake in western Montana was the strongest earthquake in the region in 60 years. An initial quake set off 10 smaller earthquakes, with people as far west as Seattle and as far north as Canada reporting feeling tremors.

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Pompeii's Eyewitness: Letters from Pliny the Younger

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Pompeii's Eyewitness: Letters from Pliny the Younger

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Ashes were already falling, not as yet very thickly. I looked round: a dense black cloud was coming up behind us, spreading over the earth like a flood.'Let us leave the road while we can still see,'I said,'or we shall be knocked down and trampled underfoot in the dark by the crowd behind.'We had scarcely sat down to rest when darkness fell, not the dark of a moonless or cloudy night, but as if the lamp had been put out in a closed room.

the atmosphere. A "firestorm" of poisonous vapors and molten debris engulfed the surrounding area suffocating the inhabitants of the neighboring Roman resort cities of Pompeii, Herculaneum and Stabiae. Tons of falling debris filled the streets until nothing remained to be seen of the once thriving communities. The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire.
A few years after the event, Pliny wrote a friend, Cornelius Tacitus, describing the happenings of late August 79 AD when the eruption of Vesuvius obliterated Pompeii, killed his Uncle and almost destroyed his family. At the time, Pliney was eighteen and living at his Uncle's villa in the town of Misenum. We pick up his story as he describes the warning raised by his mother:

"My uncle was stationed at Misenum, in active command of the fleet. On 24 August, in the early afternoon, my mother drew his attention to a cloud of unusual size and appearance. He had been out in the sun, had taken a cold bath, and lunched while lying down, and was then working at his books. He called for his shoes and climbed up to a place which would give him the best view of the phenomenon. It was not clear at that distance from which mountain the cloud was rising (it was afterwards known to be Vesuvius); its general appearance can best be expressed as being like an umbrella pine, for it rose to a great height on a sort of trunk and then split off into branches, I imagine because it was thrust upwards by the first blast and then left unsupported as the pressure subsided, or else it was borne down by its own weight so that it spread out and gradually dispersed. In places it looked white, elsewhere blotched and dirty, according to the amount of soil and ashes it carried with it.
My uncle's scholarly acumen saw at once that it was important enough for a closer inspection, and he ordered a boat to be made ready, telling me I could come with him if I wished. I replied that I preferred to go on with my studies, and as it happened he had himself given me some writing to do.
As he was leaving the house he was handed a message from Rectina, wife of Tascus whose house was at the foot of the mountain, so that escape was impossible except by boat. She was terrified by the danger threatening her and implored him to rescue her from her fate. He changed his plans, and what he had begun in a spirit of inquiry he completed as a hero. He gave orders for the warships to be launched and went on board himself with the intention of bringing help to many more people besides Rectina, for this lovely stretch of coast was thickly populated.

He hurried to the place which everyone else was hastily leaving, steering his course straight for the danger zone. He was entirely fearless, describing each new movement and phase of the portent to be noted down exactly as he observed them. Ashes were already falling, hotter and thicker as the ships drew near, followed by bits of pumice and blackened stones, charred and cracked by the flames: then suddenly they were in shallow water, and the shore was blocked by the debris from the mountain.

For a moment my uncle wondered whether to turn back, but when the helmsman advised this he refused, telling him that Fortune stood by the courageous and they must make for Pomponianus at Stabiae. He was cut off there by the breadth of the bay (for the shore gradually curves round a basin filled by the sea) so that he was not as yet in danger, though it was clear that this would come nearer as it spread. Pomponianus had therefore already put his belongings on board ship, intending to escape if the contrary wind fell. This wind was of course full in my uncle's favour, and he was able to bring his ship in. He embraced his terrified friend, cheered and encouraged him, and thinking he could calm his fears by showing his own composure, gave orders that he was to be carried to the bathroom. After his bath he lay down and dined; he was quite cheerful, or at any rate he pretended he was, which was no less courageous.

Meanwhile on Mount Vesuvius broad sheets of fire and leaping flames blazed at several points, their bright glare emphasized by the darkness of night. My uncle tried to allay the fears of his companions by repeatedly declaring that these were nothing but bonfires left by the peasants in their terror, or else empty houses on fire in the districts they had abandoned. Then he went to rest and certainly slept, for as he was a stout man his breathing was rather loud and heavy and could be heard by people coming and going outside his door. By this time the courtyard giving access to his room was full of ashes mixed with pumice stones, so that its level had risen, and if he had stayed in the room any longer he would never have got out. He was wakened, came out and joined Pomponianus and the rest of the household who had sat up all night.
They debated whether to stay indoors or take their chance in the open, for the buildings were now shaking with violent shocks, and seemed to be swaying to and fro as if they were torn from their foundations. Outside, on the other hand, there was the danger of failing pumice stones, even though these were light and porous; however, after comparing the risks they chose the latter. In my uncle's case one reason outweighed the other, but for the others it was a choice of fears. As a protection against falling objects they put pillows on their heads tied down with cloths.

Elsewhere there was daylight by this time, but they were still in darkness, blacker and denser than any ordinary night, which they relieved by lighting torches and various kinds of lamp. My uncle decided to go down to the shore and investigate on the spot the possibility of any escape by sea, but he found the waves still wild and dangerous. A sheet was spread on the ground for him to lie down, and he repeatedly asked for cold water to drink.

Then the flames and smell of sulphur which gave warning of the approaching fire drove the others to take flight and roused him to stand up. He stood leaning on two slaves and then suddenly collapsed, I imagine because the dense, fumes choked his breathing by blocking his windpipe which was constitutionally weak and narrow and often inflamed. When daylight returned on the 26th - two days after the last day he had been seen - his body was found intact and uninjured, still fully clothed and looking more like sleep than death.

You could hear the shrieks of women, the wailing of infants, and the shouting of men; some were calling their parents, others their children or their wives, trying to recognize them by their voices. People bewailed their own fate or that of their relatives, and there were some who prayed for death in their terror of dying. Many besought the aid of the gods, but still more imagined there were no gods left, and that the universe was plunged into eternal darkness for evermore.

There were people, too, who added to the real perils by inventing fictitious dangers: some reported that part of Misenum had collapsed or another part was on fire, and though their tales were false they found others to believe them. A gleam of light returned, but we took this to be a warning of the approaching flames rather than daylight. However, the flames remained some distance off; then darkness came on once more and ashes began to fall again, this time in heavy showers. We rose from time to time and shook them off, otherwise we should have been buried and crushed beneath their weight. I could boast that not a groan or cry of fear escaped me in these perils, but I admit that I derived some poor consolation in my mortal lot from the belief that the whole world was dying with me and I with it."

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Ashes were already falling, not as yet very thickly. I looked round: a dense black cloud was coming up behind us, spreading over the earth like a flood.'Let us leave the road while we can still see,'I said,'or we shall be knocked down and trampled underfoot in the dark by the crowd behind.'We had scarcely sat down to rest when darkness fell, not the dark of a moonless or cloudy night, but as if the lamp had been put out in a closed room.

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How didn't they know what was going to happen?

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Newsela | Lost Cities: Pompeii, preserved by disaster, risks ruin all over again

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Flickr / Howard Ignatius

Yellowstone National Park may be best known for its Old Faithful geyser and its stunning wildlife, but the national park also sits atop a supervolcano that simmers just under the surface.

You can see evidence of the volcano's active state in the park's famous hydrothermal activity, including Old Faithful, which shoots water every few hours.

Because the area's still active, researchers have been trying to determine when it might erupt again. And according to new research presented at the International Association of Volcanology and Chemistry of the Earth's Interior conference, it might take much less time for the supervolcano to go from not a problem to erupting than experts realized. Based on minerals from the last major eruption, the researchers found that the changes leading up to an eruption may happen in a matter of decades rather than thousands of years in advance as previously thought.

"It's shocking how little time is required to take a volcanic system from being quiet and sitting there to the edge of an eruption," Hannah Shamloo, a graduate student at Arizona State University who conducted the research told The New York Times.

Even so, she said, it's still too early to determine an exact time scale of when the supervolcano will erupt. And scientists still don't think Yellowstone's supervolcano will erupt anytime soon (at least not in the next thousand years).

What constitutes a supervolcano

Supervolcanoesare characterized as volcanic centers that have had eruptions that covered more than 240 cubic miles. The US has two: one in Yellowstone and another in California's Long Valley.

Yellowstone has had three major volcanic events in the past 2.1 million years, which led to the creation of the calderas, or large craters.

BI Video

The last volcanic eruption there happened about 174,000 yearsago, and it led to the formation of the West Thumb Geyser Basin, which extended the Yellowstone Lake.

The impact of an eruption

The odds of the supervolcano erupting within a given year are one in 730,000, according to the US Geological Survey. But if it did blow, it could have extreme effects on surrounding areas.

For starters, the eruption could emit ash that would expand over 500 miles. For comparison, this map shows the area that the ash reached in the 1980 Mount St. Helens eruption in Washington.

BI Video

The eruption would likely cover the ground with as much as 4 inches of gray ash, which could be detrimental to crops growing in the Midwest.

Molten lava at temperatures up to 1,000 degrees Fahrenheit could also ooze out, though that'd be less of a concern than the ash. And the supervolcano would spew a whole bunch of gasses as well, including sulfur dioxide, which can lead to acid rain as well as global cooling as it reflects sunlight away from the Earth.

The explosion likely wouldn't wipe out human life, but it certainly would be destructive, especially to the western half of the US.

In the meantime, researchers are keeping a close watch on Yellowstone to check for warning signs that an eruption might be underway.

SEE ALSO: Elon Musk wants to colonize Mars with SpaceX but has yet to explain how people will survive there

NOW WATCH: There's a live supervolcano underneath Yellowstone National Park - here's what would happen if it erupted

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A deadly supervolcano lies under Yellowstone - and an eruption would emit dangerous gases and spread ash for 500 miles

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Yellowstone National Park may be best known for its Old Faithful geyser and its stunning wildlife, but the national park also sits atop a supervolcano that simmers just under the surface. You can see evidence of the volcano's active state in the park's famous hydrothermal activity, including Old Faithful, which shoots water every few hours.

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CLOSE

A magnitude-6.4 earthquake rocked Taiwan on Tuesday, killing at least two people, injuring more than 100, toppling buildings and damaging roads, authorities said.

The U.S. Geological Survey said the quake was centered 13 miles north-northeast of Hualien, a city of more than 100,000 on Taiwan's east coast. Photos and videos posted on social media show toppled and leaning high-rise buildings and badly damaged roads.

Multiple, strong aftershocks rattled the area, keeping residents and emergency officials on edge.

"Armed forces & government agencies are responding. Relief measures are underway. Stay safe," Taiwan President Tsai Ing-wen tweeted.

Taiwan's CTI -TV reported at least five buildings collapsed in the city. The high-rise Marshal Hotel caved-in, and 116 people were evacuated from the 11-story building after the bottom three floors were crushed, firefighters told Taiwan's state-owned Central News Agency.

The Hualien Shangxiao Road Community Apartment suffered severe damage and was tilted 45 degrees, the first and second floors almost completely crushed, Taiwan News reported. Rescue workers estimated the building contained more than 80 households.

Landslides triggered by the quake closed some vital highways.

Military spokesman Chen Chung-chi told CNA that 88 military members had been dispatched to aid the rescue missions,with 250 more expected to be sent soon.

The quake, at a depth of less than six miles, came two days after another strong temblor struck off Taiwan's east coast. The earthquake could be felt across Taiwan, CNA reported.

Earthquakes are a fairly common occurrence in Taiwan, which sits on the boundary of two tectonic plates - the Philippine Sea Plate to the East and the Eurasian Plate.

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Powerful Taiwan earthquake kills 2, topples buildings

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CLOSE A magnitude-6.4 earthquake rocked Taiwan on Tuesday, killing at least two people, injuring more than 100, toppling buildings and damaging roads, authorities said. The U.S. Geological Survey said the quake was centered 13 miles north-northeast of Hualien, a city of more than 100,000 on Taiwan's east coast.

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Name 3 things you can do to prevent injury before or during an earthquake?

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Thursday:
Review your BrainPop Questions, then take the BrainPop Earthquakes Quiz!!

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1-1-1
Tell me ONE thing you knew already, ONE thing you learned today, and ONE thing you still want to know!

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Wednesday:
What do you notice about the USGS graphic? How does this information fit with what you already know about Earthquakes and seismic activity?

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Live video - 7.8 earthquake, Nov 14 2016 - house shaking in Wellington, New Zealand

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This is a live video of my computer room in Wellington during the 7.8 earthquake from Kaikoura. In Wellington this was rated as a Modified Mercalli Intensity (MMI) 7 event. It was quite some earthquake, about 1 minute 20 seconds from first shaking till it stopped.

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https://newsela.com/read/govt-science-earthquakes/id/26756/

Annotate:
-Main Ideas
-Words you don't know
-Interesting facts you find

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https://newsela.com/read/Wisconsin-earthquakes/id/4834/

Annotate:
-Main Ideas
-Words you don't know
-Interesting facts you find

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https://www.brainpop.com/science/earthsystem/earthquakes/

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http://s.newsweek.com/sites/www.newsweek.com/files/styles/embed-lg/public/2015/04/28/indian-and-eurasian-plates.jpg