On February 21st, 2018 we learned about

Tsunamis may soon be detected with a single hydrophone and a decent amount of math

Tsunamis aren’t subtle, but they do still manage to be surprising. They’re created by earthquakes under the sea, sometimes so far from a coast that people will have no idea any seismic activity occurred. Then, once the surge of water reaches a shoreline, anyone there has very little time to react and escape the area. As we get better at monitoring the ocean floor for earthquakes, these events are becoming slightly easier to predict, but the sea floor is so vast that it’s not the most practical endeavor. However, new research is suggesting that the key to catching tsunamis earlier may come down to listening to the sea, and acoustic gravity waves in particular, in just the right way.

Massive amounts of movement

When an earthquake occurs in the ocean, there’s obviously a lot of shaking and vibrating going on. In addition to massive amounts of displaced water, a quake will send out acoustic gravity waves (AGWs) in every direction. These waves are a bit like a hybrid of sound waves moving laterally through the air, and the gravity-sensitive waves you see shaping fluids like the average waves near a beach. This has made AGWs tricky to study and model, since they don’t follow the exact patterns we see in more common wave activity. One trait that has stood out, however, is that an AGW can move through the ocean at the speed of sound across huge distances. Because of their impressive sizes and speeds, researchers have long hoped that they could be detected well in advance of a tsunami’s arrival, buying people more time to get to safety.

The difficulty hasn’t been detecting the AGWs, but making sense of them. Fortunately, scientists from the University of Cardiff are now suggesting that this kind of analysis is not only possible, but practical even with only a single hydrophone sensor in the ocean to detect the wave. The distinct shape and speed of any AGW should reveal various aspects about the earthquake that created them. With more information in the system, such as details about the suspected fault location, researchers state that the tsunami’s amplitude and potential impact on a shoreline can be predicted. Once compiled, these data could then be used to trigger tsunami alarms in the tsunami’s path, giving people crucial time to find safety.

Heard through single hydrophone

On a basic level, this is similar to the tsunami alarms we have today. Devices known as dart buoys are anchored at sea, and can then detect unusual pressure changes in the water below them. This works if the buoys are in the tsunami’s path, which then requires that they’re located in all the right locations at all the right times. Measuring AGWs, however, don’t require that kind of specific placement. Because AGWs expand in multiple directions from an earthquake’s epicenter, hydrophones in any direction could detect clues about the formation of a tsunami. This then leads to a much more practical system for early warnings, increasing the chances that an alarm will reach people with enough time to get away from the water.

Source: Could underwater sound waves be the key to early tsunami warnings? by Cardiff University, Science Daily

On January 15th, 2018 we learned about

Sifting through the causes, concepts and misconceptions of quicksand

Despite growing up in tame suburban landscape of sidewalks and lawns, my kids are very concerned about how to deal with quicksand. I can only assume that repeated viewings of Wreck It Ralph and The Force Awakens (no Princess Bride yet) have helped build up the mystery of watery sand, particularly since fiction usually portrays it as something perilous that can capture a hero without warning. Of course, having seen DuckTales and G.I. Joe, I know that my kids’ concerns are unfounded, and that we’ll never run into quicksand near our home. Or so I thought.

Sources of soupy sand

Well, I was right about the general composition of quicksand. It’s any loose, grainy soil with a large concentration of water in it to turn it into a fluid. One of the most common places to run into quicksand is at the beach when water rushes into loose sand. Sand that’s only moist is likely to clump together, but with enough water flowing through the sand, each grain will separate and basically roll around independently of each other. The resulting soup can then look like solid ground from above, but has a consistency just a bit thicker than water when you step into it. While quicksand in nature is going to involve water, Mark Rober has a great demonstration of how sand can behave like a fluid using air as well.

Now, not every puddle turns into quicksand, obviously, mainly because the water needs to flow in a way that helps separate the grains of sand or soil. A great way to break up clumped soil turns out to be vibrations from earthquakes, and tremblors are a major cause of quicksand in all kinds of environments. Quake-produced quicksand is actually a significant safety hazard, not so much for people suddenly in need of conveniently placed vines, but for buildings that partially sink into the ground, stressing or warping their structural integrity. As such, researching the exact combinations of vibrations, soil composition and water flow has been the subject of research looking to predict which locations are most likely to suddenly turn to soup when the ground shakes.

Saving yourself from sinking

Aside from our next trip to the beach, the intersection of quakes and quicksand adds sudden legitimacy to my kids’ concerns about sinking into the soil. We don’t live especially close to a marsh or lake, but earthquakes aren’t uncommon in the Bay Area. Unless a water pipe bursts at just the right spot, it still seems unlikely that we’ll run into quicksand nearby, but there aren’t many conveniently placed vines to grab hold of if we did. Despite what cartoons and movies have taught us, that’s probably ok, since most quicksand isn’t likely to swallow you up in the first place.

While drowning in fluidized soil can happen, most instances of quicksand in nature aren’t that deep, so you aren’t likely to be fully submerged in order to drown. You might get stuck though, and trying to lift your legs straight up to take a step would be very difficult. Your best option is to try to lean back and spread your arms, letting buoyancy help lift you up. Small movements of your legs will help loosen them, but sharp vertical yanks aren’t going to be practical. This isn’t to say that people don’t die after getting stuck in quicksand, but some of those cases are due to other factors, like rising water levels, than the quicksand on its own.

Source: How Quicksand Works by Kevin Bonsor, How Stuff Works

On January 4th, 2018 we learned about

Fossilized microbes show surprising biodiversity from 3.4 billion years ago

Most rocks on the Earth’s surface don’t last more than 200 million years before erosion or other forces get the best of them. Sure, that’s older than any dinosaur, but it’s only a tiny slice of our planet’s 4.5-billion-year history. Thankfully, rocks and crystals from the Earth’s early days do turn up here and there, helping us understand what our planet once looked like, and even more intriguing, who first called it home. That latter point is being revealed by 3.4-billion-year-old rocks from Australia, which have been found to not only contain fossilized microorganisms, but evidence of a surprisingly diverse ecosystem at a time when our planet was just beginning to be habitable.

Combing through fossils for traces of chemistry

The fossilized microorganisms weren’t multicellular animals of course, so these ancient rocks offered no bones or organs to study. Instead, researchers studied each singled-celled organism with secondary ion mass spectroscopy (SIMS). This technology allowed researchers to compare variations of carbon atoms, or isotopes, in the fossils and surrounding stone. The ratios of carbon-12 to carbon-13 was then be used to determine how each microbe functioned when it was alive, as those isotopes will accumulate differently in different metabolic conditions.

Differences in these early prokaryotes‘ metabolisms suggest that even 3.4 billion years ago, life had evolved a few different ecological niches. One group was apparently a methane producer, while another powered its metabolism by consuming methane. A third fossil showed signs of primitive photosynthesis that, unlike today’s plants, didn’t produce oxygen (which would have been toxic to these organisms). A microbe from an earlier study rounds out the bunch, as it relied on sulfur as its primary food-source.

Is life less unusual than we assumed?

This version of Earth certainly wouldn’t be habitable by today’s standards, but it’s an amazing degree of sophistication for a planet that had probably only had solid ground for 600 million years. This suggests that either the Earth was intensely lucky at an early age, or that life may be a bit more tenacious than we once thought. If it’s the latter, researchers suspect that this aggressive microbial timeline may have played out on other planets as well. It wouldn’t mean that other planets have the same complex organisms we do here, but that getting some microbes growing in the first place isn’t such a long-shot.

Until we get probes out to places like Europa, Titan or Enceladus, the best location to find extraterrestrial microbes may be Mars. This wouldn’t be to find microbes alive today, but to look for traces of similar fossils from the days when Mars was likely a more habitable planet.

Source:

On November 27th, 2017 we learned about

Most of the mammoths found trapped in hazardous terrain turn out to be male

One of the most important features of the La Brea Tar Pits in Los Angeles are the traffic cones. The museum’s collection of Pleistocene animals is great, as are the continuing excavations taking place at the site, like Project 23. However, having just returned from my kids’ first visit to the Tar Pits, I think the entire experience was greatly enhanced natural liquid asphalt bubbling out of the ground in the surrounding Hancock park. Some bigger pools are fenced off, but it’s clear that the asphalt is slightly unpredictable, sometimes oozing outside a barrier, or simply popping up in the middle of the lawn, with only an oil-splattered traffic cone to warn you of its sticky presence. It all helps drive home just how animals living in the Los Angeles basin 60,000 years ago might have gotten into trouble without the bright green cones in place to warn them.

The La Brea Tar Pits weren’t the only natural hazards Ice Age animals had to worry about, and a recent study of mammoth (Mammuthus primigenius) remains from Siberia looked for patterns in which creatures most often got themselves into these sticky situations. Excavations of geological dangers like asphalt pools and icy lakes had already established that one trapped herbivore was likely to attract huge numbers of carnivores (that would also end up trapped), but this study looked to see which particular mammoths couldn’t stay out of the asphalt, ice or other pitfall. Since these animals were well preserved from only 60,000 years ago, DNA from hair and bones could be used to determine that 69 percent of the trapped mammoths were male, despite having originated from a balanced population.

Males in the muck

Researchers suspect that, if mammoths follow some of the behaviors seen in their modern elephant relatives, the unusual sex-ratio was due to male mammoths’ inexperience. Elephants today generally rely on the leadership of an older female, and that matriarch retains and transmits information about everything from when to migrate to how to avoid hazards in their environment. Young male elephants have to figure all this out themselves, even if it means finding out the hard way.

If mammoths lived in a similar manner, the males likely fell into pits and asphalt pools more often because they had nobody to teach them until it was too late. A higher tolerance for risk may have also made them more likely to try stepping on the weird black stuff in the grass, since without a matriarch or green traffic cone to warn them, they weren’t sufficiently wary of what now seems like an obvious danger.


My third grader asked: What’s the asphalt made of?

liquid asphalt bubbling up in Hancock Park
Liquid asphalt bubbling up in Hancock Park, Los Angeles.

While male mammoths were apparently adept at getting stuck in all kinds of hazards, the pachyderms in what would become Los Angeles were stuck in a natural asphalt, which is the lowest grade of crude oil. This oil is a layer of decomposed, pressurized marine plankton, first laid down five to 25 million years ago. The bubbles are generally methane gas, although microorganisms in the oil help create hydrogen sulfide, which adds a notable “rotten egg” smell.

It’s not clear how ancient mammoths missed the bubbles and the smell, but once dust and leaves covered the surface of a shallow oil pool, it seemed to only take a few steps to completely ensnare mammoths and other megafauna.

Source: Woolly Mammoth Bachelors Skew the Fossil Record by Carl Engelking, D-brief

On November 2nd, 2017 we learned about

Sediments suggest that the asteroid that destroyed the dinosaurs also triggered years of freezing temperatures

You’d think that mass extinction would be devastating enough, but every new detail that scientists uncover about the asteroid impact that wiped out the dinosaurs seems to somehow make a bad situation even worse. To the best of our knowledge, a six- to nine-mile-wide asteroid hit the Earth near the Yucatan Peninsula 66 million years ago, kicking off a series of catastrophes that resulted in the death of 75 percent of all living things. To glean even more detail about this traumatic event, scientists have been analyzing the rock and soil that was laid down at the time of impact in what’s known as the Chicxulub impact crater. What they’ve found is that on top of everything else, the world was plunged into a deep freeze that lasted up to three full years. And if that somehow wasn’t enough, there’s also a good chance that the whole thing stunk like a bad fart.

When the asteroid hit the Earth, so much debris was kicked up that it left a clear layer of sediment around the world, now known as the Cretaceous-Paleogene boundary. The rock layers at the crater itself offer a more granular picture of how this debris was distributed though, even revealing the exact angle of the asteroid’s impact. By comparing differences in composition on either side of the crater, researchers calculated that the asteroid was traveling at around 40,000 miles per hour, striking what was once a shallow sea at around a 60 degree angle. It instantly created an 18-mile-deep hole, although that pit was short lived as the walls collapsed inwards within minutes of the collision.

Sulfur saturates the skies

Beyond the crater itself, gigatons of material from the Earth and asteroid were vaporized in this violent process. Thanks to these new samples, researchers have amended earlier estimates about the composition of this material, all of which point to a colder, stinkier way to die. Smaller amounts of sulfur are associated with the smell of rotten eggs or fragrant hot springs, and can be combined in to poisonous compounds under the right conditions. In this more cataclysmic scenario, thousands of billions of tons of sulfur were ejected into the atmosphere, blanketing the planet in a layer of noxious gas thick enough to block sunlight. This general model isn’t new, but the amount of sulfur in these new figures far exceeds previous estimates. Instead of simply making photosynthesis difficult for plants on a darkened world, it’s now thought that global temperatures dropped by 47° Fahrenheit, dropping below freezing in many locations. This instant winter then lasted for at least three years, but possibly well over a decade.

The other measurement to come out of this visit to Chicxulub didn’t soften things at all. Looking at carbonates as a measure for the amount of carbon dioxide released during the asteroid’s impact, researchers realized that previous estimates had been too generous. There was still an impressive 425 gigatons of CO2 released, but that wasn’t enough of the greenhouse gas to really counteract the cooling effects of the sulfur in the air. Eventually things warmed up again, but the immediate jolt to global temperatures was clearly too much for most ecosystems to survive.

Source: Asteroid impact plunged dinosaurs into catastrophic 'winter' by Jonathan Amos, BBC

On October 1st, 2017 we learned about

An emptied Mediterranean Sea enabled an increase in volcanic eruptions

Earthquakes can be bad. Earthquakes blocking off a key water source are likely worse. Earthquakes blocking water that eventually trigger volcanic eruptions would be… ridiculous? It may sound like a script to a summer blockbuster from the 1990s, but this story actually took place in the Miocene Epoch, around seven million years ago, leaving the Mediterranean Sea dry enough to walk across. The ground, and water levels, have obviously moved again since that time, but layers of earth all around the Mediterranean still tell the story the Messinian salinity crisis, when the sea was walkable and apparently lined by unusually active volcanoes.

Sediment layers under the sea

In cliffs along the Mediterranean, you can see layers of salt and gypsum crystals that were deposited thanks to evaporating seawater. It’s not surprising to see those sediment patterns in cliffs now exposed to the Sun, giving evidence to higher water levels long ago. The plot thickened in 1961, when researchers drilling under the Mediterranean Sea found the same patterns under water. For evaporation to have laid down salt and gypsum there, the only explanation was that what’s now the bottom of the sea was temporarily exposed to the Sun, although more than sunshine would have been required to dry up 965,300 square miles of water.

The loss of water was thanks to some major earthquakes near the strait of Gibraltar. As the European and African tectonic plates ground into each other, land was pushed up, blocking up the flow of water between the Atlantic ocean and the Mediterranean Sea. Without a regular supply of new water, the Mediterranean Sea was more susceptible to evaporation, drying up up enough to loose a half-mile of depth in places where water remained. The Sea started to look more like lakes, and which a new study suggests is what started to make some local mountains look more like volcanoes.

Water goes down, magma comes up

As much as we associate magma with being hot water with being cool, the big issue here was actually weight. Water is heavy enough to simply weigh down the ground, demonstrated recently by the 0.8 inches Houston, Texas was measured to have dropped under the weight of Hurricane Harvey’s rainfall. The dried Mediterranean greatly reduced the pressure on the ground below it, which allowed magma to more easily rise to the Earth’s surface. As a result of the magma’s freed movement, the rate of volcanic eruptions in the area more than doubled, with at least 13 eruptions taking place around 5.9 to 5.4 million years ago. To put it in a nutshell, blocking up the water effectively unblocked the magma.

Since the Mediterranean doesn’t currently look like Mordor, it’s easy to surmise that these changes were all reversed at some point. Another series of earthquakes reopened the strait of Gibraltar bit by bit, allowing the Atlantic to come rushing back in. Sediment layers suggest that these floods occurred more than once, although it’s unknown if that would have made for another disaster movie, or just welcome relief from the salty land and extra eruptions.


My kids asked: What about animals that got stuck out there when the water was gone and came back?

These transitions were probably difficult for most organisms. Even as water slowly dried up, the increased salinity would have giving many marine species a run for their money in whatever water remained. At least a few animals probably wandered out when the water was low, only to be isolated on newly defined islands when sea levels returned to normal. Once trapped on an island, it’s likely that some species underwent island dwarfism or gigantism thanks to the environmental pressures of living in a very different space than their ancestors did.

Source: Disappearance of Mediterranean Sea Seven Million Years Ago Triggered Widespread Volcanic Activity by David Bressan, Forbes

On September 19th, 2017 we learned about

Speculation about why the ancient Greeks repeatedly rebuilt on earthquake fault lines

Despite what housing prices in the San Francisco Bay area may suggest, most people have an understanding of how dangerous living on an earthquake fault-line can be. It helps that since San Francisco’s historic quake in 1906, a lot of research has been done on what causes earthquakes, leading to more safely engineered buildings that can survive a tremblor. Of course, before people even considered the notion of plate tectonics, seismically active locations have been surprisingly active real estate markets. In fact, there’s a chance that the occasional shake-up actually attracted people, since they interpreted earthquakes as being divine in origin.

Guessing why the ground shakes

Geologist Iain Stewart from the University of Plymouth noticed an odd trend in building locations in ancient Greece, as many cities, temples and monuments were built directly on active fault lines. On it’s own that’s not that odd, but the fact that ancient people’s repeatedly rebuilt ruined structures at these locations indicates that there was a strong motivation to do so. Without scientific explanations and predictions to help shape people’s reactions, Stewart suspects that the ground’s spontaneous movement was likely understood to be an expression of the gods’ will. Even if a building was shaken to dust, knowing that a deity had taken an interest in a particular plot of land boosted its prestige as a sort of ‘holy’ site.

In some cases, the intersection of geology and faith is fairly clear. The famed Oracle of Delphi described visions that foretold the future and explained the actions of the gods. While the accuracy of those interpretations may be up for debate, a biochemical component has been found for the seer’s visions, as ethylene gas was likely produced underground, and released with each bit of seismic activity. The priestess was then probably subject to hallucinations, and would share the her descriptions of these sights as guidance for her visitors. Similarly, an oracle at Perachora Heraion may have lost their divine gift after a quake blocked off a water supply to vision-inducing hot springs in 300 BC.

Picking fault lines on purpose?

Even ignoring these more mind-altering interactions with fissures in the rock, Stewart believes that the ancient Greeks weren’t rebuilding on fault lines at random. It’s hard to move a city to avoid seismic activity, but it should have been possible to a least move a broken temple off a fault. Instead, Stewart things the Greeks rebuilt at the same locations on purpose, possibly to harness the inexplicable energy of that spot. While Stewart has a list of at least four more cities that seem conspicuously located along active fault lines, he admits that he’s looking at this from a geologist’s perspective. He’s hoping that archaeologists will look for evidence of people’s intent to build where the ground shook, helping answer how they rationalized living in such a risk-prone place.

As for the Bay Area… the weather really is lovely most of the year, and the local produce is hard to beat, plate tectonics be damned.

Source: Ancient Greeks May Have Deliberately Built Sacred Sites on Earthquake Faults by John Dyer, Seeker

On July 24th, 2017 we learned about

Meteorites may have delivered the metals we find on Earth and Mars

Even if you’ve visited a mine, you still might not appreciate where metals come from. Humans have been digging metals out of the ground for thousands of years, but we’ve only been digging that metal out of the planet’s crust. This is weird, because when the Earth was forming billions of years ago, most of the precious metals like gold and platinum sank to the planet’s core with the iron that now dominates that space. That should have made those metals inaccessible to anyone on the surface, and yet we happily make use of these metals on a daily basis. It’s quite possible that the metal we find in the Earth’s crust actually came from space.

Assuming that our “native” gold, platinum, copper and more are all buried in the center of the planet, the shiny stuff we do dig up would have started on a meteorite. Billions of years ago, its hypothesized that a barrage of meteorites covered the Earth with a fresh supply of metals. Some of those metals were simply buried in the planet’s crust, while others may have been absorbed as deep as the mantle where they could have been churned and moved to new locations. Over time, some of these metals could have been pushed closer to the surface thanks to seismic activity, leaving us with situations like ancient Cyprus, where copper was found in such abundance we named the metal after the island.

Massive impacts on Mars

A twist on this model has also been proposed for other planets. Mars currently lacks the tectonic activity that could have moved and brought metals to its surface, and yet the Red Planet’s southern hemisphere seems to have plenty of metals that shouldn’t be there. That region also has a lot of scars from ancient impact craters, which helps support the idea that the metals on the surface of Mars were also delivered via meteorite billions of years ago.

In the proposed model, a huge meteor hit the planet, not only loading it with a new supply of metals, but also kicking up debris that would eventually coalesce into at least one of Mars’ two moons. It’s a tidy hypothesis, and it fits well with everything from concepts surrounding how planets are formed to why the surface of Mars’ northern hemisphere appears to be a different age than the southern hemisphere.

Source: Where does all Earth's gold come from? Precious metals the result of meteorite bombardment, rock analysis finds, Science Daily

On July 11th, 2017 we learned about

Study links subtle, subterranean vibrations to future volcanic activity

Volcanoes would be a lot easier to deal with if they were a bit more predictable. People live in the shadow of volcanoes around the world, often hoping that the richness of the soil created by the magma-spewing structures will outweigh the potential risk of fiery, toxic annihilation. Fortunately, volcanoes like Kīlauea in Hawaii are actually pretty consistent and thus relatively easy to work with. Kīlauea has been erupting since January 3, 1983, and that constant activity has made a great place to test technologies that might help us predict the eruptions of more volatile volcanoes elsewhere.

Two ways to monitor magma

Researchers from the University of Cambridge have been looking at two potential signals that, when taken together, may act as an early warning for eruptions. The first line of data concerned vibrations in the ground around the volcano. There’s often a fair amount of energy pulsing through rock and dirt from a variety of sources, many of which have nothing to do with moving lava. But over the course of four years, patterns could be detected in the speed of the vibrations shifting through the ground. To help make better sense of this low-intensity activity, two sensors were compared, looking for vibrations that started close to one and then moved to the other. This would help filter out seismic activity that originated elsewhere, and thus wasn’t directly tied to Kīlauea.

The second line of data concerned larger changes in the shape of Kīlauea itself. As magma moves through different layers of earth, heat and pressure changes create deformities in the volcano itself, particularly in the main magma chamber below that feeds the volcano. These can sometimes lead to bigger movement, such as when Kīlauea opened up a new ‘waterfall’ of lava into the ocean after a large hunk of mountain fell away.

Anticipating eruptions

Putting these data together, researchers are looking at the intersection of all this activity. As the magma chamber fills up, the overall mountain bulges and shrinks. This helps speed up local vibrations in the ground that sensors can detect. Once the magma chamber fill more, pressure underground increases, which we now know further boosts the speed of the seismic vibrations in the ground. This suggests that future detectors will be able to look for these more subtle changes in vibration speeds, rather than waiting for more obvious earthquakes. This should help catch more eruptions before it’s too late for people nearby to react.

Source: 'Bulges' in volcanoes could be used to predict eruptions by University of Cambridge, EurekAlert!

On July 5th, 2017 we learned about

Crystals laced with lithium suggest that most of a volcano’s magma isn’t liquefied

As we’ve all been taught, when a volcano erupts it spews ash, noxious fumes, and molten lava— lava of course being a term to describe the melted rocks that were forced to the Earth’s surface. However, zircon crystals, which also get pushed to the surface in a good eruptions, are rewriting this a bit. Formed deep underground, variations in these crystals indicate that there’s more of a distinction between lava and magma than its location. Most of the world’s magma isn’t really a liquid at all, a fact that may help us make sense of how, and more importantly, when, volcanoes erupt in the first place.

Digging miles into the Earth to sample magma “in the wild” isn’t terribly practical, which is part of why understanding the exact state of magma under the Earth’s crust has eluded us for so long. Fortunately, zircon crystals essentially record the condition of the magma they sit in allowing us to get an idea of how hot things were before they were brought to the surface. When a crystal is heated over 1,382° Fahrenheit, it softens and absorbs lithium from it’s local environment. Scientists can then look at how much lithium has been absorbed into a crystal to determine how hot, or cool, the surrounding magma was. Based on samples from New Zealand, most magma isn’t as squishy as we’re often led to believe.

Few signs of flowing stone

This batch of crystals was brought to the Earth’s surface in an eruption 700 years ago. Before that, they’d been buried underground for over 50,000 years, giving them plenty of opportunities to be exposed to hotter or cooler magma in the region. As it turns out, very as few as 40 of those years were spent in truly liquefied rock—  most of the crystals’ time seems to have been in magma as soft as a sort of rocky slurry at best. If anything, it seems that most of the time in truly molten magma was just before the actual eruption that carried the crystals to the surface.

Researchers know that there were more eruptions before that time though, which tells them more about the composition of the buried magma. If some parts of the Taupo Volcanic Zone were hot and pressurized enough to erupt without cooking these particular crystals, it seems that the larger supply of magma is fairly compartmentalized. Hot, liquid rock can apparently form before an eruption, but doesn’t mean that the entire region is floating over a sea of molten magma. Alternatively, eruptions may occur when molten material arrives from even deeper underground, melting a path to the surface. In either case, it seems that the lava we see is very likely very freshly made, at least on geologic timescale.

Source: Magma stored under volcanoes is mostly solid by Maria Temming, Science News