15 Facts About Lava

Ulet Ifansasti/Getty Images
Ulet Ifansasti/Getty Images

Every day, the news is filled with images of the lava flows coming from Kilauea volcano in Hawaii. Previously obscure terms like laze (lava and haze), vog (volcanic and smog/fog), and pahoehoe and a'a (types of lava flows) are becoming part of the lexicon. But how much do you really know about hot molten rock? Here are 15 fascinating facts about lava.

1. LAVA IS MAGMA ABOVE GROUND.

Magma describes molten rock when it's below the surface, while lava describes molten rock after it erupts. It might seem like a trivial distinction, but there are differences, especially after the liquid cools down. Both magma and lava produce igneous rocks when they cool, but underground magma tends to cool slowly and produce gigantic mineral crystals in a subset of igneous rock called plutonic. On the surface, lava tends to cool rapidly, creating tiny mineral crystals in a subset called volcanic. This means that the same source material can produce two different rocks depending on where it cooled; for example, granite and rhyolite are considered similar, except granite is plutonic, being formed underground, while rhyolite, created on the surface, is volcanic.

2. THERE ARE DIFFERENT TYPES OF LAVA …

lava from an erupting volcano flows and explodes
Richard Bouhet/AFP/Getty Images

The vast majority of lava out there falls into one of three types: mafic, intermediate, and felsic. They're also called basaltic, andesitic, and rhyolitic lavas, respectively. (There are other types, but they're very rare.) These three lavas are distinguished by their mineral composition, viscosity, and the amount of volcanic gases—like water, carbon dioxide, and sulfur dioxide—dissolved in the liquid.

An estimated 90 percent of lava flows are mafic, consisting of around 50 percent silica (SiO2). This kind of lava has the lowest viscosity and gas content; it's the classic bright-red flow you probably picture when you think of lava. Intermediate lava, around 60 percent silica, has higher gas content and viscosity, causing it to explode. Mount St. Helens was an intermediate eruption. Even more explosive—but rare—are felsic lavas, which are 70 percent silica and have the highest gas content and highest viscosity, often exploding and producing bits of rock called tephra.

3. … AND DIFFERENT TYPES OF LAVA FLOWS.

Specifically, there are different kinds of mafic lava flow. The major types on the surface are a’a and pahoehoe, two terms that come from Hawaiian. A’a flows rapidly and loses heat, which increases the viscosity and creates a distinctive rough surface on the cooled lava flow as pieces start breaking off; the word may be from the Hawaiian for burn or stony. In contrast, pahoehoe is smooth and is frequently described as looking like a twisted rope because it moves more slowly and has a lower viscosity, so any breaks are quickly healed. The word may ultimately derive from the Hawaiian for paddle, to describe the smooth ripples paddles create in water. When an eruption occurs under the ocean, a third type called pillow appears. Aside from being underwater, pillow flows are frequently difficult to distinguish from pahoehoe.

4. THE SHAPE OF A VOLCANO IS INFLUENCED BY THE KIND OF LAVA INSIDE IT.

The more liquid mafic lava forms broad, gently sloped shield volcanoes, such as the main volcanoes on the Hawaiian islands. But that's not the only type of volcano this kind of lava can produce: Silica-rich mafic rocks can spray out in the air dramatically, landing back in the area they erupted from to create either a spatter cone, when the lava lands and remains liquid, welding the lava together, or a cinder cone, when the lava solidifies in the air and lands as rock. And if the lava comes from large cracks, it may form flood basalts (as mafic lava is also called).

The more viscous intermediate and felsic lavas produce stratovolcanoes (also known as composite), which are the classic volcano of popular imagination, like Mount Fuji, that build up steeper slopes.

Even more felsic lava leads to calderas, which are areas that erupted so violently the volcano collapsed into the now-emptied magma chamber, creating a large depression in the ground. (You may have even visited one: Yellowstone National Park, which sits above a dormant supervolcano, has a large caldera.) Very felsic lavas can also produce lava domes, which are formed when lava that has been degassed before an eruption piles up around the vent; according to the University of Oregon, the domes can occur in the craters or on the sides of stratovolcanoes and calderas—and sometimes even away from volcanoes altogether.

5. HUMANS HAVE BEEN FASCINATED BY LAVA FOR THOUSANDS OF YEARS …

The earliest depiction of a volcanic eruption was thought to be 8500 years old, located on a mural in the Neolithic settlement of Çatalhöyük, in what is now Turkey. (Some say it's not an eruption at all, but a leopard skin.) But there may be documentation of an eruption that's many thousands of years older. The cave paintings at Chauvet-Pont d'Arc, located 22 miles from France's Bas-Vivarais volcanic field, date to about 37,000 years ago. Alongside the standard cave-painting animals, there are also unusual markings that look like sprays, which led some French researchers to speculate that these are likely depictions of a previously unknown volcanic eruption.

6. … AND HAVE TRIED TO STOP IT FOR CENTURIES.

lava flows through metal fence
USGS via Getty Images

The earliest known attempt to stop the flow of lava was in 1669, when Mount Etna erupted on the island of Sicily. Diego Pappalardo of Catania led a group of men to open a hole in the hardened side of the lava flow; the idea was that the lava would flow out the side hole, away from their town. This was at first a success—at least for the residents of Catania. But was a potential disaster for the people of Paterno, who realized the rerouted flow was now threatening their town. They chased Diego and his men away. The hole they'd made in the hardened lava soon clogged, and the lava resumed its original path towards Catania, where it met the city wall. The wall apparently lasted several days before it failed, and lava entered the city. Sicilians had better luck in 1983 and 1992, when their attempts to divert lava flow from Mt. Etna using earthen banks and concrete blocks were moderately successful. Iceland, too, managed to contain some damage from a 1973 eruption by spraying lava with seawater.

7. WE TRIED TO BOMB LAVA INTO SUBMISSION.

In 1935, the U.S. Army bombed a lava channel on Hawaii's Mauna Loa to divert the flow heading towards Hilo. It didn't work. They tried again in 1942 during another eruption of Mauna Loa—and it still didn't work. However, a few days after the 1942 bombing, there was a natural collapse on the volcano that brought the lava flow to a halt. In theory, bombing a channel can make the lava slow down and do less damage to cities because lava moves fastest when contained in a channel or a lava tube, while lava that flows in a broad fan is much slower and cools faster.

This knowledge inspired yet more experimentation three decades later, in 1975 and 1976, when the Air Force dropped aerial ordnance on ancient lava fields on Mauna Loa to see what would happen. They found that spatter cones were particularly vulnerable to bombing. In a report, the Air Force concluded, "Modern aerial bombing has a substantial probability of success for diversion of lava from most expected types of eruptions on Mauna Loa's Northeast Rift Zone, if Hilo is threatened and if Air Force assistance is requested." Despite this assertion, the technique has never been attempted again.

8. THE CAUSE OF HAWAII'S VOLCANISM IS MYSTERIOUS.

In general, volcanoes form near the edges of plates and are side effects of plate tectonics, but Hawaii is thousands of miles from a plate boundary. To explain this and similar anomalies, geologists proposed the "hot spot" hypothesis. The idea is that a plume of extremely hot material comes from the core-mantle boundary and shoots up, punching a hole in the crust and creating islands like Hawaii. Later refinements to this theory proposed that the plume is more or less stationary, and as the crust moves over the plume it creates features like the Hawaiian island chain.

But as Earth magazine explains, this has proven easy to propose and nearly impossible to verify. Critics complain that as contradicting data has emerged, the hot spot hypothesis has become so flexible that it has stopped actually being useful. Instead, a new hypothesis ties these mid-plate features to plate tectonics. In the case of Hawaii, because the Pacific plate is subducting, or going beneath, other tectonic plates in both Asia and parts of North America, it's starting to crack—and thanks to local mantle conditions the Hawaiian volcanoes are forming. Even as the eruption is nightly news, the cause of volcanism in Hawaii is undergoing renewed debate.

9. IT'S PRETTY EASY TO OUTRUN A LAVA FLOW …

people on road in hawaii taking photos of lava from kilauea volcano
Frederic J. Brown/AFP/Getty Images

Last year, researchers from the University of Bristol looked at volcano fatalities between the years 1500 and 2017. Of more than 214,000 deaths they recorded, only 659 could be attributed to lava flows, because, they wrote, "lavas normally advance slowly, allowing escape.” The USGS says a typical mafic lava on a gentle slope flows at less than 1 mph; steep slopes and lava tubes increase that speed.

According to the Bristol researchers, what you really need to watch out for are explosions. "Sudden outbursts of very fluid lavas can cause loss of life," they wrote. "Deaths and injuries typically arise if escape routes are cut off, or as small explosions occur through interaction with water, vegetation or fuel."

Most fatalities could be attributed to "pyroclastic density currents"—basically hot gas, rocks, and ash moving at high speed—which were responsible for 60,000 deaths, or volcano-related tsunamis, which killed about the same number of people. Another nearly 50,000 people were killed by lahars, or volcanic mudflows of water and debris. The remaining deaths were caused by a mix of secondary lahars (which occur years after an eruption), tephra, avalanches, landslides, gas, flying killer rocks called ballistics, and—in nine cases—lightning.

10. … BUT THEY CAN STILL BE DEADLY.

The single largest loss of life from lava occurred in the Democratic Republic of Congo in 2002 when an estimated 100 to 130 people were killed by lava when the Nyiragongo volcano erupted. Situated near the city of Goma, the eruption displaced 250,000 people (another 150,000 are thought to have stayed) as lava flowed through the city streets and cut off parts of the town, including covering an estimated 80 percent of the airstrip at the local airport. Beyond its proximity to a major city, Nyiragongo is deadly because it's believed to have some of—if not the—fastest lava on Earth. A 1977 eruption of Nyiragongo created lava—an extremely low-viscosity mafic type—that traveled at an estimated 40 mph. The 2002 flow is thought to have been slightly slower.

11. BLUE LAVA ISN'T REAL …

Frequently making the rounds on social media are images of "blue lava" from the Indonesian volcano Kawah Ijen. Sadly, the amazing blue glow isn't actual lava. Instead it's caused by sulfuric gases that emerge at high temperatures and ignite, which then can flow down as a glowing liquid sulfur. Blue flames caused by ignited methane gas from burned plant matter are appearing in Hawaii as well.

12. … BUT BLACK LAVA IS.

The coolest (by temperature) lava in the world is at Ol Doinyo Lengai in Tanzania. Lava generally ranges from 1300°F–2300°F (700°C –1250°C), depending on its composition. But the lava at Ol Doinyo Lengai is only around 1000°F. It's also the world's only known active carbonatite volcano (a carbonatite is an igneous rock that's mostly carbonate minerals), which means instead of flowing red, the lava flows black and then solidifies white. The ultimate origin of the weird lava at Ol Doinyo Lengai is still a matter of debate, but because it's responsible for much of the world's rare-earth element production, it's increasingly being studied for economic reasons.

13. THERE'S A RESTAURANT THAT USES LAVA TO COOK FOOD.

If you find yourself wanting a unique experience on the island of Lanzarote in the Canary Islands, there's a restaurant called El Diablo. What makes it unique is that the grill is placed on top of a 6-foot deep hole with lava at the bottom (although it's considered safe as the last eruption was in 1824). Dining here might be a better choice than trying to roast marshmallows over a volcanic vent, which the USGS strongly advised people not do, noting that even if it weren't dangerous to be near a vent, the sulfur dioxide and hydrogen sulfide likely being emitted would make your marshmallow taste awful.

14. MARS MAY HAVE LAVA CHANNELS.

Whether the deep channels on the surface of Mars were caused by lava or water is hotly debated by researchers. It may seem like it would be easy to tell the difference, but in 2010, researchers analyzed a lava flow from 1859 in Hawaii and found features that looked very similar to channels on Mars that were thought to be carved by water. They concluded that fast and low-viscosity lavas could create many of these features that we thought were water-made. A 2017 study came to a similar conclusion on a different part of Mars, saying that what's traditionally seen as signs of rivers and lakes in one region "can be better explained by fluid lava flooding the channels and filling pre-existing impact craters."

15. CLEANING UP LAVA CAN TAKE MONTHS OR YEARS—IF IT HAPPENS AT ALL.

lava cools as it flows across a field in Hawaii
USGS via Getty Images

Returning a landscape to normalcy up after a volcano can be difficult. If a lot of ash has built up, proper care must be taken to dispose of the ash at a dedicated site all while avoiding inhaling glass, fine silica dust, and toxic gases into the lungs, which could lead to serious illness. Lava is even more difficult. According to Accuweather, contractors rarely fully remove the hardened lava, which can take months or years to completely cool. Even then, removing the lava—which is now rock—requires specialized tools. "In the Hawaii case, we are talking about lava that is incredibly sticky and viscous, and that is nearly 2000°F," University at Buffalo volcanologist Greg Valentine told Digital Trends. "No house can stand up to that, and even if it could, it would be partly or completely buried when everything is over." For these reasons, most people just start anew.

England Is Being Invaded By a Swarm of Flying Ants That Can Be Seen From Space

Digoarpi/iStock via Getty Images
Digoarpi/iStock via Getty Images

Last week, the UK's weather service registered what seemed like a system of rain showers moving along the nation’s southern coast. But it wasn’t rain—it was a swarm of flying ants.

Though it sounds like something out of a horror film or the Old Testament, it’s actually a completely normal phenomenon that occurs in the UK every summer when a bout of hot, humid weather follows a period of rainfall, The Guardian reports. Flying ants decide it’s a good time to mate, and the queen takes to the sky, emitting pheromones that attract males.

From there, it’s survival of the fittest. The queen will out-fly most of her suitors, leaving only the strongest males to catch up and mate with her, which ensures the strength of her offspring. The others either lose their wings and fall to the ground, or become bird food. (The ants produce formic acid in their bodies as a defense mechanism, which may make gulls that eat them seem loopy.)

According to Smithsonian.com, the queen will chew off her wings after mating and fall to the ground to start a new colony, and the sperm she collected from that one flight will fertilize her eggs for the rest of her life (which could be up to 15 years in the wild).

The official, rather-romantic term for the annual aerial antics is “nuptial flight,” but locals often refer to it simply as “flying ant day.” It sometimes lasts for weeks, during which billions of the harmless insects can be seen in the skies.

A representative from the Met Office explained that its weather satellites mistook the ants for rain clouds because the radar detects the ants in the same way it sees raindrops. Dr. Adam Hart, an entomologist at the University of Gloucestershire, told The Guardian that he thinks the reason the radar registered the ants this year was a result of better satellite technology rather than an increase in the flying ant population.

[h/t Smithsonian.com]

Why Does Humidity Make Us Feel Hotter?

Tomwang112/iStock via Getty Images
Tomwang112/iStock via Getty Images

With temperatures spiking around the country, we thought it might be a good time to answer some questions about the heat index—and why humidity makes us feel hotter.

Why does humidity make us feel hotter?

To answer that question, we need to talk about getting sweaty.

As you probably remember from your high school biology class, one of the ways our bodies cool themselves is by sweating. The sweat then evaporates from our skin, and it carries heat away from the body as it leaves.

Humidity throws a wrench in that system of evaporative cooling, though. As relative humidity increases, the evaporation of sweat from our skin slows down. Instead, the sweat just drips off of us, which leaves us with all of the stinkiness and none of the cooling effect. Thus, when the humidity spikes, our bodies effectively lose a key tool that could normally be used to cool us down.

What's relative about relative humidity?

We all know that humidity refers to the amount of water contained in the air. However, as the air’s temperature changes, so does the amount of water the air can hold. (Air can hold more water vapor as the temperature heats up.) Relative humidity compares the actual humidity to the maximum amount of water vapor the air can hold at any given temperature.

Whose idea was the heat index?

While the notion of humidity making days feel warmer is painfully apparent to anyone who has ever been outside on a soupy day, our current system owes a big debt to Robert G. Steadman, an academic textile researcher. In a 1979 research paper called, “An Assessment of Sultriness, Parts I and II,” Steadman laid out the basic factors that would affect how hot a person felt under a given set of conditions, and meteorologists soon used his work to derive a simplified formula for calculating heat index.

The formula is long and cumbersome, but luckily it can be transformed into easy-to-read charts. Today your local meteorologist just needs to know the air temperature and the relative humidity, and the chart will tell him or her the rest.

Is the heat index calculation the same for everyone?

Not quite, but it’s close. Steadman’s original research was founded on the idea of a “typical” person who was outdoors under a very precise set of conditions. Specifically, Steadman’s everyman was 5’7” tall, weighed 147 pounds, wore long pants and a short-sleeved shirt, and was walking at just over three miles per hour into a slight breeze in the shade. Any deviations from these conditions will affect how the heat/humidity combo feels to a certain person.

What difference does being in the shade make?

Quite a big one. All of the National Weather Service’s charts for calculating the heat index make the reasonable assumption that folks will look for shade when it’s oppressively hot and muggy out. Direct sunlight can add up to 15 degrees to the calculated heat index.

How does wind affect how dangerous the heat is?

Normally, when we think of wind on a hot day, we think of a nice, cooling breeze. That’s the normal state of affairs, but when the weather is really, really hot—think high-90s hot—a dry wind actually heats us up. When it’s that hot out, wind actually draws sweat away from our bodies before it can evaporate to help cool us down. Thanks to this effect, what might have been a cool breeze acts more like a convection oven.

When should I start worrying about high heat index readings?

The National Weather Service has a handy four-tiered system to tell you how dire the heat situation is. At the most severe level, when the heat index is over 130, that's classified as "Extreme Danger" and the risk of heat stroke is highly likely with continued exposure. Things get less scary as you move down the ladder, but even on "Danger" days, when the heat index ranges from 105 to 130, you probably don’t want to be outside. According to the service, that’s when prolonged exposure and/or physical activity make sunstroke, heat cramps, and heat exhaustion likely, while heat stroke is possible.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article has been updated for 2019.

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