00:00Phew, you can finally send that last report for the day and breathe out.
00:04The weekend is around the corner, but just when you're about to hit send,
00:08you're alarmed by the low rumbling under your desk.
00:11Is it the light rail passing by?
00:13Unfortunately, that's not the case.
00:16It's a volcano speaking.
00:18What, here? In Arizona?
00:21That's right, the ground keeps shifting under Arizona,
00:24reminding us that Earth is alive.
00:26No panic, though. Let's arm ourselves with some context.
00:3120 American states have extinct, active, and dormant, currently sleeping, volcanoes.
00:38Among such states, you can find California,
00:42New Mexico,
00:44Nevada,
00:46Utah,
00:47and Colorado.
00:49On the bright side, Arizona's volcanoes are dormant at the moment,
00:53but it doesn't mean they won't go off in the near or not-so-near future.
00:58Now, how about traveling to Arizona to check the traces of its active volcanic past?
01:05They dot the desert landscapes of this state like spots dot a Dalmatian.
01:09There are entire volcanic fields southwest of Phoenix,
01:14east of Douglas,
01:17near Flagstaff,
01:19north of Kingman,
01:21and near the Mexico border.
01:24The most worrying thing about these fields is that even though they're not active at the moment,
01:30eruptions in this region might happen every thousand years or so.
01:33Well, the time seems to be up.
01:37The last powerful and destructive volcanic eruption occurred around 1,000 years ago at the Sunset Crater.
01:44Oh, this place is worth paying more attention to.
01:47And we will, but a bit later.
01:50First, we have to talk about hotspots.
01:53No, not that place where you can surf the web.
01:55In our volcanic context,
01:58a hotspot is a place where insane amounts of heat melt the overlying crust,
02:03Earth's thin outer layer,
02:04and form volcanoes.
02:06This heat rises from the mantle,
02:08which is located between our planet's dense,
02:11superheated core and the crust.
02:15Want to see an example of this type of volcanism?
02:18Welcome to the Hawaiian Islands.
02:20The Big Island has its active volcanoes because,
02:24at the moment,
02:25it's situated on top of the Hawaiian hotspot.
02:28The older Hawaiian islands were once there too,
02:31but later they drifted off towards the northwest.
02:35It happened because that's where the oceanic crust on top of which they sat,
02:39namely the Pacific Plate, moved.
02:43Now, look at the world's ocean basins.
02:45Yes, they're literally dotted with islands that sit on top of hotspots,
02:49like Hawaii,
02:51Iceland,
02:53Samoa,
02:54the Galapagos.
02:55Those are probably the most famous examples.
02:58But don't think that continents can't host hotspots.
03:01They can.
03:02But those are far less common.
03:04One of the most famous continental hotspots is,
03:07ah, I bet you know it.
03:09Yep, the one beneath the Yellowstone Caldera.
03:13By the way,
03:14the caldera is a vast volcanic crater,
03:16especially one formed as a result of a massive eruption
03:19that led to the collapse of the mouth of a volcano.
03:24The Yellowstone hotspot is basically the creator of Old Faithful
03:28and the rest of the hot springs and mudpots for which the National Park is famous.
03:32Speaking of Old Faithful,
03:35let's make a small detour and pay more attention to this wonder of nature.
03:40It's one of the most well-known geysers in the world.
03:43People have been coming from all over the globe to see it for more than a century.
03:48The cool thing about this geyser
03:50is that the likes of it can only form under very specific conditions.
03:55That's why they're pretty rare.
03:56Magma under the surface superheats pockets of underground water.
04:02The pressure there keeps growing
04:04until it eventually pushes the water upward with immense strength.
04:09A certain volcanic rock with a high silica content
04:12lines the tunnel through which this water escapes.
04:15Basically, it creates a unique pipe
04:17that can withstand unbelievable pressure and heat
04:21created by the water erupting above the ground.
04:23Old Faithful was the very first named geyser in Yellowstone.
04:29If you come to visit it expecting the thing to erupt every hour on the hour,
04:33you're going to be disappointed.
04:36On average, Old Faithful erupts every 91 minutes or so,
04:39which isn't that bad either.
04:41Plus, you can download a special app
04:43which will provide you with the approximate time of the next eruption.
04:47But be very careful while visiting and stay away from the site.
04:51The water erupting from the powerful geyser reaches 204 degrees Fahrenheit.
04:57The steam is even more scorching, up to 350 degrees Fahrenheit.
05:02It's hot enough to bake a cake.
05:05But let's get back to our volcanic hotspots.
05:09Scientists still don't clearly understand
05:11why there aren't many hotspot volcanoes on continental crust.
05:15One reason might be that the continental crust is much thicker than the oceanic crust,
05:21which is about four times as thick on average.
05:25Another reason could be that most of Earth's crust, about two-thirds of it, is oceanic.
05:31This means that there's less continental crust for hotspots to form under.
05:35Now, I bet those of you living in Arizona will appreciate the following info.
05:42We'll talk about a volcanic field right in the heart of this state.
05:46The San Francisco Volcanic Field.
05:49That's a massive area filled with over 600 volcanoes.
05:53Yes, they're mostly small, but it doesn't make them any less impressive.
05:57They're scattered across 1,800 square miles in northern Arizona, a giant territory.
06:04Interestingly, scientists are still debating about whether this volcanic field
06:08is actually sitting on top of a hotspot.
06:11But one thing they agree upon,
06:13the volcanoes in this area get younger as you move east.
06:17And this pattern matches up with the North American plate
06:20moving west over what could be
06:22a stationary hotspot beneath the surface of our planet.
06:26Cool, huh?
06:27The volcanic Hulapaloo in that area started around 6 million years ago.
06:34So, in geological terms, it's relatively young.
06:38As for the most recent eruption, it happened less than 1,000 years ago.
06:43The Sunset Crater, which I mentioned before, the one near Flagstaff,
06:47is the most famous vent from that eruption.
06:50The Sinagua people had to leave their homes at Wupatki Pueblo because of the eruption.
06:54That site is now part of the Wupatki National Monument.
06:59There, you can see how people lived in this volcanic region many years ago.
07:03If you go to explore this area, you'll notice that most of the volcanoes there are basalt cinder cones,
07:11small and steep.
07:12The Colorado Plateau has quite dry weather conditions.
07:17That's why the volcanoes haven't worn down much.
07:19Some of the best examples of those cones, like this one, called the SP Crater,
07:24still look like they appeared yesterday.
07:29But look around.
07:30It's not just cinder cones.
07:32The San Francisco volcanic field also has a stratovolcano,
07:37as well as some lava domes that formed from volcanic rocks with more silica than basalt
07:42you can find in places like Hawaii.
07:44It means they're thicker and don't flow as easily.
07:49Anyway, the stratovolcano is going to be one of the most epic sights you'll come across
07:53while exploring this volcanic field.
07:56Well, not the stratovolcano itself, but the San Francisco peaks,
08:00the remains of that giant formation.
08:02They stand tall at more than 12,600 feet.
08:07That's four and a half Burj Khalifas placed on top of one another.
08:11It makes the peaks some of the biggest landmarks in northern Arizona.
08:16They're not only stunning, but also sacred to the Native American people
08:20who have lived in the area for many generations.
08:25Now, unlike those superactive volcanoes in Hawaii,
08:28the San Francisco volcanic field takes its time.
08:32Thousands of years between eruptions.
08:35But you shouldn't relax just yet.
08:37Geologists say another eruption is likely to happen one day.
08:42It will probably occur in the remote eastern part of the field,
08:45away from big towns.
08:47Phew!
08:48And if that next eruption is anything like the one that formed Sunset Crater,
08:53it would be quite the show.
08:55Lava fountains and rivers of lava flowing.
08:58At the same time, the next eruption might not happen for centuries.
09:02Maybe even millennia.
09:05Until then, the San Francisco volcanic field will remain a hidden gem of volcanic history,
09:11waiting for its next fiery performance.
09:13Lava fountains.
09:14M
09:25No
09:25T
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