Robin George Andrews

Lateiki was a tiny island in the archipelagic Kingdom of Tonga, formed in 1995 by an ebullient submarine volcano. Last month, that underwater fire starter decided it was time for some explosive redecorating.

An eruption in the southwest Pacific Ocean was first reported Oct. 14 by a Tongan ship. The Tonga Geological Service then scanned through satellite imagery and noticed the paroxysm, at Lateiki, began a day earlier. During the next week or so, various vessels, flights and satellites intermittently saw an ashy plume rising from the island.

By Nov. 1, it was all over; Lateiki was gone, its remnants swallowed by the volcano’s erupting maw. But this loss of Tongan territory was short-lived. As quickly as Lateiki self-destructed, it was reborn as a new island roughly 400 feet to the west. The new Lateiki, 1,310 feet long and 330 feet wide, is nearly four times the size of the old one.

Lateiki is highly practiced in the art of volcanic makeovers. Several of its eruptions reportedly built ephemeral shoal islands in the 18th and 19th centuries, and more definitively in 1967 and 1979. Until 1995, these islands lasted a few months before being chewed up by the waves.

Submarine volcanism can be difficult to study and observe. But Lateiki’s cycles of death and rebirth give scientists clues to the nature of the magmatic machinations below. And with improving satellite technology, they can be documented better than ever before.

“To see this process happening in our lifetime is pretty spectacular,” said Janine Krippner of the Smithsonian Institution’s Global Volcanism Program.

Sitting midway between the islands of Kao and Late, Lateiki — formerly known as Metis Shoal — is just one member of an extended family of volcanoes. It sits on the Tonga-Kermadec volcanic arc, a 1,740-mile-long trench that delineates where the Pacific plate dives beneath the Australian plate. This titanic tectonic battle fuels many volcanoes in the southeast Pacific, from New Zealand’s North Island to the northern tip of the Tongan archipelago.

In August, an unnamed volcano along that spine erupted, producing a San Francisco-sized raft of pumice. Lateiki is just the latest fiery fountain on the arc to put on a show.

The ability of Lateiki to migrate may seem strange. But new vents can pop up anywhere along the volcano’s 3-mile-long, flat-topped surface, creating islands in different locations.

“I was a little surprised that the old island completely disappeared,” said Ed Venzke, who oversees the database of volcanoes at the Global Volcanism Program.

The 1995 island had been partly eroded by waves over the past quarter-century, but nevertheless resisted complete annihilation because it was made of solid clumps of sticky, solidified lava. But the violence of October’s eruption finally seemed to cause it to collapse.

It is too early to forecast how long the new Lateiki will persist, said Brad Scott, a volcanologist at GNS Science in New Zealand. Until someone takes a closer look, it is impossible to say how easy it may be for the ocean, or another volcanic explosion, to take it out.

Its construction materials matter. Havre, another submarine volcano on that arc, erupted in 2012, producing a pumice raft 155 square miles across. But no island was created, because pumice, formed when lava quickly quenches in seawater and traps gas, is buoyant, not adhesive, and easily drifts away. Gloopy, degassed lava flows erupting at shallow depths are far better at building islands.

If the new Lateiki does stick around, it may end up like Japan’s Nishinoshima or Iceland’s Surtsey: other pop-up volcanic islands that, after the embers had cooled, became citadels of marine, microbial and avian life.

This article originally appeared in

This Volcano Destroyed an Island, Then Created a New One

(Trilobites)

There’s something new in Yellowstone National Park, and it’s hot and corrosive. It’s also “been sneaking up on the park for the last 20 years” and has grown to be the size of four soccer fields, said Greg Vaughan, a research scientist with the Yellowstone Volcano Observatory.

That’s not anything to worry about. Carved by ancient volcanic activity and peppered by ever-changing, kaleidoscopic natural beauty, Yellowstone, the world’s oldest national park, is monitored extremely closely by scientists. As it covers a whopping 3,472 square miles across three states, you can’t expect them to spot every single new natural feature the moment it appears.

But with some satellite sleuthing, the emerging warm spot has finally been discovered by Vaughan and his colleagues, who reported the discovery in a blog post on the Yellowstone Volcano Observatory’s website this month.

This thermal area is the newest addition to a family of many thousands of geothermal features at Yellowstone that are often mercurial and occasionally hyperactive.

Its discovery not only helps scientists better understand how the park is evolving but also cements the notion that there really is nowhere else like it on the planet. This type of activity might be unusual for other volcanoes, Vaughan explained, but for Yellowstone, this state of geological excitability is perfectly normal.

“It’s doing everything you expect an active volcano to do except erupt,” he said.

Vaughan’s job is to use satellite imagery to map out, measure and monitor thermal areas of the park. Looking through the Landsat 8 satellite’s thermal infrared imagery taken in April 2017 during a routine survey, he serendipitously spotted a strange and previously undetected bright feature just south of the Tern Lake Thermal Area within the park, indicating a relatively hot patch was present.

Ruling out the possibility of a warm lake, he turned to the National Agriculture Imagery Program, operated by the Department of Agriculture, to find further clues. Every few years, during agricultural growing seasons in the contiguous United States, the government flies over the country and takes high-resolution pictures of the vegetation below. Sometimes, these flight paths cover Yellowstone.

Vaughan perused the aerial shots taken of the suspicious region. In 1994, nothing seemed amiss and trees were growing healthily. However, from then through 2017, trees had perished and the soil had turned a sickly off-white color. The only reasonable explanation was that a new thermal area had been covertly growing in the region since the late 1990s, altering the ground’s chemistry with its superheated fluids.

Helen Robinson, a geothermal expert at Glasgow University in Scotland, speculated that the precipitation of minerals within cracks or fault lines in the nearby Tern Lake Thermal Area may have sealed off an old pathway for circulating superheated groundwater. Consequently, the groundwater has been forced to find an alternate route to the surface, leading to the creation of a new thermal area.

The U.S. Geological Survey defines a thermal area as a contiguous section of the ground that contains at least one thermal feature, such as a hot spring or a geyser, as well as hydrothermal mineral deposits, altered rocks and dead vegetation. As with plenty of thermal areas, this new one cropped up in a remote part of the park, which means experts have not yet visited to see what features it contains.

Many thermal areas come and go, says Michael Poland, the scientist-in-charge at Yellowstone Volcano Observatory, so the appearance of a new one isn’t anything to worry about.

Like all the park’s geothermal activity, this new warm spot is not directly connected to the underlying and mostly solid magma reservoir, so its emergence is not a sign that the volcano is about to blow its top. It’s simply Yellowstone safely letting off some steam.

This article originally appeared in <a href="https://www.nytimes.com/2019/04/12/science/yellowstone-volcano-warm-spot.html" id="68cad8f1-d92a-343a-a42b-ff95a82a755d">The New York Times</a>.

It's Warm and Stealthy, and Has Killed Yellowstone Trees and Turned Soil Pale

Faced with the prospect of a sizable asteroid heading toward Earth and causing doomsday, humanity has come up with various responses.

Hollywood may reckon that the best way to destroy an errant space rock is with nuclear weapons. This is rarely the preferred option of experts, but using some sort of spacecraft system to smash an asteroid into small, harmless pieces is seen as a real-world possibility. A new study, looking at a gigantic space rock-on-space rock clash, hints at how utterly ineffective this type of asteroid assassination attempt may be.

Using computer models, scientists simulated a 4,000-foot asteroid smashing into a 15.5-mile asteroid at 11,200 mph. Immediately after colliding, the large asteroid cracked considerably, with debris flowing outward like a cascade of Ping-Pong balls. Despite some deep fractures, the heart of the asteroid was not comprehensively damaged.

As time went on, the gravitational pull of the asteroid’s resilient core was able to pull back ejected shards. It seems that asteroids don’t just absorb mind-boggling amounts of damage, but, as previous work has hinted, they also are able to rebuild themselves.

Charles El Mir, who studies asteroid annihilation at Johns Hopkins University and is the paper’s lead author, said his findings “could be interpreted as an argument against ‘blowing up’ an asteroid as a defensive strategy.”

Asteroid collisions and demolitions have been simulated many times in recent decades. Earlier studies suggested that large asteroids are full of internal scars because of their violent history, and that a fast enough impact would completely shatter them.

The new study, published this month in the journal Icarus, tried a different simulation.

K.T. Ramesh, director of the Hopkins Extreme Materials Institute, said that Andy Tonge, a former graduate student, had developed a computational model that looked at how materials like bulletproof vests respond to impacts. Realizing that Tonge’s model could simulate asteroid impact events, the team merged it with another model that also replicated the effects of a large asteroid’s gravitational field.

This hybrid model allowed them to more realistically see how an asteroid responds to being hit by a powerful projectile. It captured previously missing but vital small-scale details, including where fractures would appear and precisely how they would spread.

Michele Bannister, a planetary astronomer at Queen’s University Belfast, described the research as “a nice upgrade on modeling the complex physical realities” of the solar system’s enigmatic rocky monsters.

The study has limitations. Both asteroids are modeled as simple, nonrotating chunks of rock, whereas real asteroids are far more variable. In addition, the larger asteroid, despite featuring a starting collection of cracks, did not have a history of multiple impacts as true asteroids would. A large space rock smashing into a humongous space rock also differs from a missile onslaught, or an atomic bomb exploding on or beneath an asteroid’s surface while a popular rock band plays.

The study doesn’t rule out using projectiles to destroy an incoming asteroid, El Mir said. But, he added, shattering a large asteroid may end up causing more problems than it solves. Turning a cannonball into shotgun-shell fragments could still result in Armageddon if the shards strike Earth.

NASA’s Planetary Defense Coordination Office, which keeps an eye on asteroids and comets that will one day pass close to Earth, instead suggests changing a space rock’s trajectory by giving it a small nudge well in advance of reaching our world. NASA and others aim to test this strategy in 2022 with the Double Asteroid Redirection Test, in which a spacecraft will deliberately crash into the smaller member of a binary asteroid system in an attempt to change its orbit around the larger body.

Ultimately, the choice between deflection and destruction largely depends on how quickly an incoming asteroid is spotted.

“A successful deflection becomes more difficult to execute as warning time decreases,” said Megan Bruck Syal, a planetary defense researcher at the Lawrence Livermore National Laboratory. “For the shortest warning times, robust disruption and dispersal of the fragments may be the only viable option to prevent the impact.”

This article originally appeared in <a href="https://www.nytimes.com/2019/03/08/science/asteroids-nuclear-weapons.html" id="06294f1d-e4d2-3329-a9f7-d4781fcf24f7">The New York Times</a>.

If We Blow Up an Asteroid, It Might Put Itself Back Together

Anthony Cook, an astronomical observer at Los Angeles’ Griffith Observatory, which streamed the eclipse, thought it could have just been the camera’s random electronic noise. Then astronomers and citizen scientists started to share their detection of the flash on Reddit and Twitter.

The only explanation was that something slammed into the lunar surface and obliterated itself.

The moon is a multibillion-year-old library of impact events, with fresh collisions still taking place frequently. Capturing a lunar impact on video is rare enough, but capturing this event — a collision during a total lunar eclipse — may have been a first.

“I have not heard of anyone seeing an impact like this during a lunar eclipse before,” said Sara Russell, a professor of planetary sciences at the Natural History Museum in London.

Russell said that flashes can be seen from Earth only when the lunar surface is in shadow, which is normally just a few days before and after the new moon. A luminous full moon is anathema to such detections, but a total lunar eclipse, painting our pale celestial companion in darkness, changed that.

Justin Cowart, a graduate student in geosciences at Stony Brook University in New York who spotted the flash, managed to narrow down the impact location. Using images from an amateur astronomer, Christian Fröschlin, Cowart determined that the flash took place somewhere in the lunar highlands, south of Byrgius crater.

NASA’s Lunar Reconnaissance Orbiter, which studies the moon’s surface, may soon spot the fresh crater. But the impact flash itself can be used to roughly estimate the size of the object that crashed on the moon, and its momentum. Based on NASA and European Space Agency databases of impact flashes, Cowart guesses that “it was probably somewhere between the size of an acorn and tennis ball.”

Detection data from the Moon Impacts Detection and Analysis System, or MIDAS, found that the space rock was a pipsqueak of a meteoroid, only weighing something like 22 pounds, and measuring no more than 12 inches across.

The provenance of the meteoroid remains an open question. According to Jose Maria Madiedo, an astrophysicist at the University of Huelva in Spain who is a co-director of the MIDAS system, most objects that hit Earth come from comets and not asteroids, and the same applies to the moon.

With that in mind, he said, “the most likely situation is that the impactor was a rock from a comet.”

Considering its tiny dimensions, it must have been moving at an incredible speed to create a flash of light visible from Earth. Indeed, Madiedo said that the impact speed would be in the range of 38,000 mph. That is just over twice the speed that NASA’s old space shuttle had to move after launch to achieve orbit of Earth.

A total lunar eclipse is always something to marvel at, but one being gate-crashed by a hypersonic cometary shard is something else entirely.

This article originally appeared in <a href="https://www.nytimes.com/2019/01/23/science/lunar-eclipse-meteor-moon.html" id="680531e9-6d4f-3f1c-a9b3-c8f81e6b1893">The New York Times</a>.

During the Lunar Eclipse, Something Slammed Into the Moon

On Sunday and Monday, those in the Western Hemisphere with clear skies were fortunate enough to see the last total lunar eclipse of the decade. As the moon took on a distinctly redder shade just before midnight Eastern time, livestreams of the phenomenon showed a flash of light suddenly and briefly emanating from the lunar surface.

Now the U.S. Geological Survey’s Hawaiian Volcano Observatory and other scientists have published the first detailed summary of this paroxysm. The landmark study, published in the journal Science on Tuesday, unspools a timeline of this volcano’s most destructive eruption in recorded history and shows that it contained a combination of volcanic events that has seldom been observed.

Thanks to an unparalleled monitoring effort, volcanologists have gained a deeper understanding of America’s most hazardous volcano, which may help reveal the secrets of similar volcanoes around the world. What follows is a summary of key volcanic events in Kilauea’s 2018 outburst, in the order in which they occurred.

May

Kilauea is one of several active volcanoes on the island of Hawaii, the archipelago’s largest. Found in the island’s southeast corner, it has been erupting continuously since 1983. But by May of this year, a new eruption sequence had commenced, with two focal points: a flank area known as the lower east rift zone, a point where the volcano’s surface is gradually splitting apart, and the Halema’uma’u crater to the west at Kilauea’s summit.

Christina Neal, the scientist-in-charge at the Hawaiian Volcano Observatory and the study’s lead author, said this confluence of big volcanic events that went on for months meant that this eruption was “truly unprecedented in the modern record.” In fact, this was the largest such eruption from this rift zone in the last 200 years.

The collapse in April of the Pu’u O’o crater, located in the east rift zone, may have coincided with the breakdown of a subterranean barrier. That could have allowed magma at the site to flow through an established pathway toward the lower east rift zone.

On May 2, the Halema’uma’u summit crater’s lava lake — a persistent pool of bubbling lava inside the crater — began to drain and cracks appeared in the rift zone. The next day, the first fissure of many appeared in the Leilani Estates Subdivision and lava began to flow, prompting the evacuation of thousands of residents.

Increased seismic activity at the summit coincided with a magnitude 6.9 temblor beneath the volcano’s southern flank on May 4, the largest on the island in over four decades. The shaking likely resulted from a migration of magma pushing against the southern section of the volcano, which caused a fault to slip. Aftershocks continue to be felt more than seven months later.

By May 10, the lava lake within Halema’uma’u had dropped to around 1,070 feet below the crater floor as the magma below continuously migrated to the rift zone. As the underlying magmatic foundations of the summit disappeared, the entire crater floor began to subside in what would amount to 62 separate collapse events.

Major summit explosions were recorded May 15 and 17. The largest since 1924, they produced plumes 12,000 and 30,000 feet high. This activity was once thought to be driven by groundwater angrily reacting with draining magma. But Neal said that new data suggests that escaping magmatic gas drove the explosions.

June and July

By the beginning of June, 24 fissures had appeared in the rift zone, with rivers of lava flowing — some all the way to the ocean — as fast as 3,530 cubic feet per second. More than 55,000 tons of sulfur dioxide emissions were emerging each day.

With old, stagnant magma already erupted, deeper magma had emerged. Fluid, packed with dissolved gases and erupting at 2,200 degrees Fahrenheit, it led to spectacularly high fountains of lava emerging from some fissures, topping out at 262 feet.

On June 2, the largest freshwater lake on the island vaporized in only 90 minutes. A lava delta also formed at Kapoho Bay over the next two months. One fissure, No. 8, gradually became the dominant fissure of the eruption, building a spatter cone 180 feet high. Kilauea’s summit, featuring near-daily collapse events, continued to periodically deflate.

By July, several secondary phenomena linked to the lava had been observed. Hot updrafts produced by the lava contributed to pyrocumulus clouds and fire whirls. Buried vegetation also began to thermally decompose near flowing lava, releasing methane that burst into eerie blue flames.

Sulfur dioxide emissions regularly mixed with water vapor to produce a suffocating vog. The violent quenching of lava as it met the Pacific Ocean produced laze, a mixture of hydrochloric acid, glass particles and steam.

August and September

On Aug. 4, all volcanic activity abruptly declined. Seismic activity at the summit quieted and the rift zone experienced a dramatically reduced flow of lava until the last embers were extinguished. Sulfur dioxide emissions had nose-dived.

By the time the Hawaii Volcanoes National Park reopened Sept. 22, Kilauea’s lava covered 13.7 square miles of the island and there had been 1,640 feet of vertical collapse at the summit.

Scientists calculated that the collapsed volume lost from the summit roughly matched that of the amount of lava produced. Kyle Anderson, a geophysicist at the U.S. Geological Survey’s Volcano Science Center and co-author of the study, explained that with each collapse event came a surge of lava production at the rift zone.

Anderson said at a news conference Tuesday that this meant the summit and lower east rift zone were clearly interlinked in a devilish dance.

Eruption’s End

The Smithsonian Institution’s Global Volcanism Program defines an eruption as being over if the volcano has not experienced any volcanic activity across three consecutive months. Kilauea’s epilogue arrived Dec. 6, when the USGS declared that it was “very unlikely” the 2018 eruption at the rift zone would resume.

Magma still exists beneath the summit and rift zone. This means that a future eruption of some kind somewhere on Kilauea is a certainty. Whenever that occurs, scientists and disaster managers will rely on the insights gained from their close study of how the 2018 eruption unfolded to guide their response.

This article originally appeared in <a href="https://www.nytimes.com/2018/12/12/science/kilauea-hawaii-volcano-eruption.html" id="6d4d8890-7895-30ca-a16c-856edb68a6d3">The New York Times</a>.

America's Most Hazardous Volcano Erupted This Year. Then It Erupted and Erupted.

On April 30, the Pu’u O’o crater on Hawaii’s Kilauea volcano suddenly collapsed. It was the starting point for the volcano’s monthslong eruption, which went on to produce 320,000 Olympic-sized swimming pools’ worth of lava that transformed the landscape and ultimately destroyed 700 homes.

A study published Monday in Nature Geoscience suggests the moon was forged from the fires of an ocean of magma sloshing over baby Earth’s surface. If correct, this model may solve a long-standing paradox.

Lunar meteorites and samples collected during the Apollo missions show that the moon and Earth have remarkably similar geochemical fingerprints. Scientists suspect that this was likely the result of a giant impactor the size of Mars, known as Theia, that slammed into a young Earth and sent into orbit a spiral of material that coalesced into the moon.

Countless computer simulations show that this is possible, but there’s a problem. Such an impact on a relatively solid Earth would have created a moon made mostly out of Theia, not Earth (at least in simulations resulting in the Earth-moon system we observe today, complete with our 24-hour days).

Attempting to solve this paradox, some models have opted for more high-energy impacts, according to Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who was not involved with the current study. These models excavate more of Earth’s material for building the moon, but the moon’s orbit or Earth’s spin aren’t accurately reproduced without using convoluted workarounds.

The new research, led by Natsuki Hosono of the Japan Agency for Marine-Earth Science and Technology, adds what may be the recipe’s missing ingredient. During Earth’s earliest days, it was covered by a sheet of molten silicate rock. Hosono’s team wondered what would have happened if Theia had crashed into Earth at that time, rather than during a later, cooler, more solid phase.

The team used a standard moon-forming simulation but adjusted it to better replicate density changes throughout the objects. With these tweaks, they found that the magma ocean made all the difference.

Immediately after Theia’s impact, Earth’s hot, squishy layer would have violently cascaded into space in huge volumes. This material orbited and coalesced around the young Earth, forming a moon made of about 70 percent terrestrial material, far more than in older, largely solid Earth models, which came out at around 40 percent.

Robin Canup, an astrophysicist at Southwest Research Institute, said this magma-ocean model moves us some way toward explaining the geochemical mirroring of both objects, while also reproducing the way in which Earth and the moon dance around each other. “It’s a very exciting result,” she said. However, it is very different from earlier work, so the key to this model’s validity is to see if future models can replicate it.

Sara Russell, a professor of planetary sciences at the Natural History Museum in London, called this origin story compelling, but said scientists still have work to do to explain why the compositions of the moon and Earth are so similar. After all, this model still suggests that a significant percentage of lunar material is not derived from Earth.

Part of the problem is that scientists don’t have sufficient samples from which to obtain model data. Although the Apollo rocks are an important scientific resource, they came only from a small patch near the moon’s equator. “Imagine if we tried to reconstruct the entire history of the Earth using a tiny handful of samples,” she said. “We couldn’t do it.”

The next step, said Russell, is clear: We need to return to the moon, dig deep and bring home as many lunar fragments as possible.

This article originally appeared in <a id="a0a4200f-3bd7-4c78-aa7c-339da868f1af" href="https://www.nytimes.com/2019/05/01/science/moon-earth-collision.html">The New York Times</a>.

A violent splash of magma that may have made the moon

(Trilobites): The moon is far more than a largely dead orb. Our planet’s pale satellite is the creator of tides, the catcher of meteors and the only other world in the starry ocean where humanity has set foot. But scientists are still not entirely clear how it was made. Solving this mystery would not only reveal the moon’s origins, it would also help explain our own planet’s evolution.

<h1>Waterfalls are furious cascades of water, sometimes scoring the landscapes in which they flow as they obey gravity’s demands. From Iceland’s shimmering Skógafoss to the family of falls in New Zealand’s Milford Sound, they are zealous, aquatic showstoppers of the natural world.</h1>

Powerful though waterfalls may appear, there is a long-standing assumption that they can only form when permitted by other natural forces. Tectonic movement shifting rock around, alterations in sea level, a change from a resilient rock to a more easily erodible one are all ways in which external forces are believed to influence where waterfalls form.

But this paradigm may be about to change. By building a scaled-down river in their laboratory, a team of researchers demonstrated that waterfalls can sometimes bring themselves into existence without any outside help.

Scientists “often use the presence of waterfalls to try and reconstruct the history of a landscape,” said Edwin Baynes, a quantitative geomorphologist at the University of Auckland in New Zealand who was not involved in the study. By better understanding how waterfalls can form, the new study may prompt scientists to reconsider how our planet shaped itself, and help them peer back through deep geological time with greater precision.

Although there had been suggestions in the scientific literature that waterfalls could self-form, it wasn’t clear how that could occur. This new experimental evidence, said Baynes, provides a “very convincing” explanation.

To investigate how waterfalls form, researchers built a 26-foot long, 12-inch wide, 3.3-foot deep channel. They filled it with a foamy bedrock, tilted it at a 20 percent slope and let sediment-rich water flow down its surface. By using a riverbed made of foam rather than real rock, the team was able to watch millenniums of erosion play out under very short time scales.

The turbulent flow of the “river” down a steep slope started digging out parts of the riverbed. It did so unevenly, with some pockets eroding faster than others, and the uneven erosion was amplified as the river continued to quickly flow. Eventually, with no externally triggered changes to the sediment load, the flow rate, the underlying channel shape or anything else, a deep pocket of erosion formed, one that made the river jet off from the higher section of the riverbed and splash down some distance away.

A waterfall appeared, all by itself.

Scientists had assumed that waterfalls always arose from geological or climate-driven changes. “Now, I think we’re starting to call that idea into question,” said Joel Scheingross, an assistant professor of geosciences at the University of Nevada, Reno, and the lead author of the study, published Wednesday in Nature.

The research could contribute to our understanding of Earth’s landscapes. By incorrectly attributing the formation of waterfalls to external forces, scientists may be “picking out erroneous climatic or tectonic signals,” said Kate Leary, a fluvial geomorphologist at the University of California, Santa Barbara who was not part of the study. “Developing a way to discern self-formed from externally forced waterfalls would be very beneficial for teasing out these signals in tectonically active landscapes.”

The results of these experiments suggest that the steep, upstream sections of rivers in mountain ranges around the world may be particularly likely to feature self-forming waterfalls. If so, the geological histories of some of these elevated realms need to be re-examined.

Scheingross said that more research needs to be done to shore up his team’s model. But if their hypothesis is supported by additional evidence, then the genesis of waterfalls “is a more complicated picture than we originally thought,” he said.

This article originally appeared in <a id="fbd09616-387d-47fd-a295-b3b7bea3a016" href="https://www.nytimes.com/2019/03/13/science/waterfalls-self-forming.html">The New York Times</a>.

What makes a waterfall? Maybe it forms itself

Powerful though waterfalls may appear, there is a long-standing assumption that they can only form when permitted by other natural forces.

<h1>Earth’s auroras, popularly known as the Northern and Southern Lights, are indisputably beautiful. They are also, perhaps surprisingly, not mirror images.</h1>

You can imagine the two like mismatched dancers: Viewed from space, the Northern Lights may contort and groove in one direction, while the Southern Lights could perform a routine that doesn’t quite sync up with its partner’s.

Research published in December in the Journal of Geophysical Research: Space Physics, reveals that the cause of this north-south auroral asymmetry is the angle at which the sun’s solar wind and magnetic field approaches Earth.

Earth has two magnetic poles, a north and a south, much in the same way a bar magnet does. From these two poles, bunched up magnetic field lines — invisible tendrils that represent the direction and strength of this planetary bar magnet — reach out into space as the planet travels on its orbit. Like fishing lines, they catch energetically excitable particles heading our way in the solar wind. These particles slam into our atmosphere, and energy is released in the form of the colorful auroras.

As these two geographically opposed magnetic poles are reflections of each other, it was once assumed that the auroras would be the same, too. However, scientists can now see more clearly that they not only have large-scale differences in shapes, but they crop up at slightly different locations around the magnetic poles, too.

Earth’s entire magnetic field is a bit like a bubble, one that is constantly being squashed by the sun’s magnetic field and solar wind. This causes the bubble to stretch out on Earth’s nightside in the shape of a magnetic tail. Space physicists have now found that when the sun’s magnetic field is heading toward Earth in a more east-west orientation relative to Earth’s magnetic poles, it compresses our magnetic tail in a peculiar way. This makes it tilt, which triggers distortions that ultimately produce differently shaped Northern and Southern Lights.

Auroral asymmetry has been studied for decades. However, it wasn’t until the early-to-mid-2000s that scientists could use satellites to observe both auroras at the same time, which allowed space physicists to clearly see that they weren’t mirror images.

Nikolai Ostgaard,head of the Birkeland Centre for Space Scienceat Norway’s University of Bergen, and Karl Laundal helped to underscore how different the two auroras could be in 2009. But a conclusive explanation of these differences remained elusive.

This new paper, led by Anders Ohma, a doctoral candidate at Bergen, examined old images of both auroras taken at the same time by two separate satellites. By assessing the most up-to-date information about the two entities’ magnetic fields, they uncovered clear evidence that the asymmetry occurs because of the angle of the sun’s magnetic field compared to Earth’s field.

Ostgaard said that this study, for which he is a co-author, disproves a long-standing hypothesis suggesting that the collision, fracturing and eventual chaotic reassembly of Earth’s and the sun’s magnetic field lines may have caused the auroral asymmetry. But their data found that this process, known as magnetic reconnection, actually reduces the asymmetry somewhat.

Elizabeth MacDonald, founder of the first citizen science network for the auroras and a space physicist at NASA’s Goddard Research Center, said the research was useful, but she added that auroras come in a wide range of flavors. It “doesn’t explain all of the asymmetry possible in different flavors of the constantly evolving aurora,” she said.

Ohma agreed that smaller phenomena remained enigmatic, but said their work did explain large-scale auroral asymmetries.

Jonathan Eastwood, a senior lecturer of space physics at Imperial College London who wasn’t involved in the study, said the research provides interesting clues as to how planetary magnetic fields work, while also inviting us to more deeply appreciate the auroras’ aesthetic charms.

“It starts to give you a sense of how majestic and big these processes are, and how small we are,” he said.

This article originally appeared in <a id="97936b3a-e58f-4fa4-b385-0fa7890d0580" href="https://www.nytimes.com/2019/02/06/science/northern-lights-southern-lights.html">The New York Times</a>.

The Northern and Southern Lights are asymmetric dancers in the dark

Research published in December in the Journal of Geophysical Research: Space Physics, reveals that the cause of this north-south auroral asymmetry is the angle at which the sun’s solar wind and magnetic field approaches Earth.

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