This eye-catching astronaut photo shows the point where an ancient Patagonian lake has been split by a peculiar land bridge, creating two contrastingly colored bodies of water.
Lake Pueyrredón (on the left in the photo) is the Argentine half of a roughly 40-mile-long (65 kilometers) glacial lake, which stretches across the country's border with Chile in Patagonia — a region in South America that is well known for its diverse range of geographic features, including mountains, fjords, deserts and rainforests. The Chilean half of the lake is known as Lake Cochrane (not shown in this image). Both halves hold crystal-clear water that is up to 1,600 feet (500 meters) deep, giving Pueyrredón a deep blue hue when viewed from above.
Thousands of years ago, a thick sediment barrier formed across the southern section of Lake Pueyrredón, creating a new body of water known as Lake Posadas. This smaller body, which is roughly 5 miles (8 km) long, has a lighter, teal color due to its shallow water and a large influx of sediment from a nearby river, according to NASA's Earth Observatory.
Other rivers from nearby hills have previously dumped large quantities of sediment along the western shore of Lake Pueyrredón (bottom of the photo), creating a trio of fan-shaped landforms, known as deltas, that increase in size from north to south (left to right in the photo).
Wind-driven currents and waves have pushed some of this sediment from the outer edges of the two smaller deltas, creating long, thin strips of land, known as sandspits, pointing down-current.
This image, snapped from the banks of Lake Posadas, shows a close-up view of the rocky barrier that formed across Lake Pueyrredón thousands of years ago. (Image credit: Prisma Bildagentur/Universal Images Group via Getty Images)The strip of land separating Pueyrredón and Posadas looks similar to the sandspits. However, it is most likely a moraine — a barrier of sediment and larger rocks that formed along the edge of a hefty iceberg or long-lost glacier, according to the Earth Observatory.
Eagle-eyed viewers may be able to spot a narrow airstrip on the smallest delta (running almost parallel with its sandspit). While the area is largely uninhabited, it is popular with tourists, who travel to the lakes to camp, hike, fish and kayak, according to a local travel site.
Lake Posadas is also home to a unique island with a massive rocky arch (see below) that is also popular with tourists.
This photo, captured in the side-view mirror of a tourist's car, shows the famous rocky arch in Lake Posadas. (Image credit: alextorrenegra via Wikimedia)The two lakes in the astronaut photo sit within a large valley, which was carved by a massive ice sheet that once covered the area. The last remnants of this ice sheet are located in northern Patagonia, around 20 miles (30 km) west of Lake Cochrane, and have also been snapped from space by astronauts.
Patagonia is home to dozens of similar valleys and fjords that were carved out by the same massive ice slab. Around 210 miles (340 km) southwest of Pueyrredón and Posadas, a trio of ravines converge to create a rare configuration where a lake, river and glacier "touch" each other at a single point.
Mini lake meets massive glacier
A 2010 satellite photo shows the point where a small lake bisects the snowy rim of an ancient glacier on Canada's Baffin Island. The rippling, snow-rimmed structure is the last remaining fragment of a colossal ice sheet that once covered large parts of North America.
Trio of 'battleground' glaciers merge
This 2023 astronaut photo shows three glaciers merging into a single massive ice mass in the Karakoram mountains. The stripy glaciers have gained ice in recent decades, despite the effects of human-caused climate change.
World's highest frozen lake shatters
A 2024 astronaut photo shows the icy surface of Pangong Lake breaking apart in the lofty Tibetan Plateau. The point where the ice meets the water almost perfectly matches a disputed border between China and India.
'> Peculiar land bridge separates a pair of colorful lakes in Patagonia — Earth from space
Volcano deposits, known as ignimbrite, that were incised by the Lluta River in northern Chile. (Image credit: Frances J. Cooper)The original slope of the volcanic flow from Lauca Caldera was about 1.5 degrees, Adams and his colleagues wrote in the new paper. The researchers also calculated the erosion of the landscape to figure out how fast the rocks in the area were rising as the oceanic Nazca Plate pushed under the continental crust of South America, which is how the Andes were built.
They found that prior to the eruption, the uplift of the crust was no more than 0.16 mile (0.26 kilometer) per million years — quite a sluggish process. This finding corresponds to earlier work that used the formation of certain minerals within rocks to determine when a particular rock rose through the crust and approached the surface.
"There is debate over whether the Andes grew slowly and steadily over 40 or 50 million years or whether they rose extremely slowly and then popped up more recently, in the last six to 10 million years," Adams said. "Our findings, which cover a large part of the middle of that history, support the slow but steady hypothesis."
The same method could be applied to other mountain ranges worldwide, the researchers added.
'> South American 'Pompeii': Volcanic eruption 22 million years ago preserved a snapshot of the Andes forming
The 3D model of the Los Angeles basin shows that downtown LA is underpinned by up to 6.2 miles (10 kilometers) of sediment, which will likely amplify shaking from any earthquake that hits the region. That's not entirely new information, but the underground map is more precise than ever before, and it should help earthquake scientists better understand which areas of the city are most vulnerable.
"With this improved model of the basin, we now know the shape of the edges of the basin in a lot more detail," Elizabeth Cochran, a U.S. Geological Survey seismologist who was not involved in the study, told Live Science.
That's important, Cochran said, because irregular edges can focus or direct earthquake waves. In the magnitude 6.7 Northridge earthquake in 1994, Santa Monica experienced more shaking damage than expected because of the way the seismic waves traveled along the basin edge, she added.
Los Angeles sits in a sedimentary basin, a low spot where layers of sediment have accumulated for at least 15 million years. At first, the basin was underwater, so the lowest layers of these sediments were oceanic sediments. Later, when tectonic forces brought the basin onto dry land, additional sediment accumulated from the mountains nearby.
Researchers knew the general shape of the basin, but not in great detail. "Previous surveys were just linear arrays that went through just one cross section on the LA Basin, but this was the first full three-dimensional map," said Valeria Villa, a doctoral student at Caltech and co-author of the new paper describing the map, published Aug. 4 in the journal JGR Solid Earth.
A 3D-printed model of the LA sedimentary basin. (Image credit: Valeria Villa/Caltech)The data from the new map came from 273 temporary seismic stations deployed around LA. These stations detected faint earthquake waves from distant quakes that couldn't be felt by humans. The paths and timing of these waves as they traveled helped researchers build a 3D map of the rock layers below the surface.
The central part of the basin, under downtown LA, holds the deepest sediments, which could amplify shaking. The edges of the basin are thinner, with 0.6 to 2.5 miles (1 to 4 km) of sediment before the hard crystalline rock that serves as the basin's bottom.
On its own, the map doesn't tell geophysicists exactly where shaking might be the worst in the case of a big LA earthquake, but researchers can now update their models and simulations to test different scenarios, Villa told Live Science. The damage will ultimately depend on a lot of factors, such as which fault causes the quake. Los Angeles is surrounded by many faults, including the famous San Andreas, which could give off a magnitude 7.8 quake that would jolt Southern California.
One important factor in the amount of damage to buildings during such a quake is "resonance" — whether buildings shake in time with the sediments below them, Cochran said. When buildings and sediments are in resonance, the damage is worse. A better understanding of the sediment layers beneath downtown LA will help researchers ensure buildings are designed to avoid resonating with the shaking basin, she said.
"You can, for example, change the stiffness of your building and do other things to offset this effect," Cochran said. "What is important is that you know what the ground is like, and what the larger geologic structure is like, underneath the region where you are building the building to know that this could be an issue."
'> We now have an incredibly detailed map to help predict which areas of LA are the most at risk from 'The Big One' In the Kingdom of Benin, one of the oldest monarchies in West Africa, a traditional ruler known as an oba would commission a brass or bronze bust of their predecessor upon taking the throne. The bust of the past oba would then be set on an ancestral altar in the palace. But when the British Empire annexed the Kingdom of Benin into colonial Nigeria in 1897, the British looted thousands of African artifacts spanning the kingdom's seven-century history, and the country of Nigeria has asked that they be returned.
Many of the surviving ancestral commemorative heads were created in the 15th and 16th centuries by the Igun Eronmwon, a hereditary guild of brass and bronze artisans that made objects for royalty in the Kingdom of Benin. According to the CMA, Benin royalty prized brass because it does not corrode. Much of the African brass was imported from as far away as Germany.
When British forces invaded the Benin royal palace in 1897, they looted thousands of metal plaques, sculptures of humans and animal figures, and royal and personal ornaments that have come to be known as the Benin Bronzes, even though most of the objects are technically brass, an alloy of copper and zinc. The British Museum holds the world's largest collection of Benin brass artifacts — over 900 objects — which Nigeria formally requested be returned in 2021.
Some institutions have begun repatriating this historic royal art back to its homeland. A group of German museums that collectively held over 1,100 of these objects transferred ownership of them to Nigeria in 2022. That same year, the Smithsonian's National Museum of African Art transferred ownership of 29 Benin Bronzes to Nigeria. And, in 2025, the Netherlands returned 119 Benin Bronzes to Nigeria. To date, however, the British Museum has not officially returned any of the Benin Bronzes in its collection.
There is also controversy about who should have ownership of these artifacts. In 2025, the Museum of Fine Arts, Boston returned two Benin Bronzes to Oba Ewuare II, the great-great-grandson of the last oba before the 1897 British invasion. Oba Ewuare II is the Oba of Benin and custodian of Benin culture.
A full catalog of royal artifacts looted from Benin in the late 19th century can be found on the Digital Benin project website.
'> Ancestral commemorative head: A 500-year-old brass bust depicting an African king
"We think that the loss of those hormones at menopause renders those neurons more vulnerable to age-related cellular decline and pathologies like Alzheimer's," said Karyn Frick, a neuroscientist and professor of psychological and brain sciences at the University of Wisconsin-Milwaukee.
So, if falling hormone levels are a risk factor for dementia, could replacing those hormones help stave off the disease?
While the idea sounds logical on its face, studies that have looked at hormone replacement therapy (HRT) for dementia prevention have had mixed results. There are early hints that restoring estrogen during early menopause may protect brain health, but ultimately, more gold-standard clinical trials are needed to know for sure, experts told Live Science.
Support for estrogen protecting the brain
The idea that estrogen could help ward off dementia is plausible. Women are more likely to develop Alzheimer's disease than men are, and scientists think the loss of estrogen during menopause may be partly to blame, said Jennifer Bruno, an instructor of psychiatry and behavioral sciences at Stanford University.
Lab and animal studies buttress the idea that estrogen could protect brain health.
In the brain, estrogens act as neuromodulators, or chemical messengers that alter how neurons behave. Estrogen also helps neurons keep their shape. Estrogen loss in female mice triggers a drop in the number of dendritic spines — the small, bud-like bumps on neurons that receive chemical messages.
An estrogen molecule. The body's levels of estrogen fluctuate in perimenopause, and they then dramatically decline and level off during and after menopause. (Image credit: theasis via Getty Images)Researchers think that estrogen may help prevent the formation of the abnormal proteins — including one called amyloid beta — that accumulate, disrupt communication between neurons and ultimately kill cells in Alzheimer's disease. Amyloid beta is produced when a larger protein is cut the "wrong" way by an enzyme, Frick explained. Estrogen promotes the "normal" cutting of this protein, thus reducing amyloid beta, studies in lab mice show.
And estrogen may limit the buildup of a second Alzheimer's-related protein, called tau, by preventing the chemical processes that cause the tau proteins to clump together. This helps prevent the formation of tau tangles, a hallmark of Alzheimer's disease.
The hormone may also support brain health indirectly by improving sleep quality.
"It's well documented that menopausal women have difficulty sleeping, whether it's due to hot flashes or insomnia," Frick said. Estrogen can ease those nighttime hot flashes, thus helping menopausal women get more, less-fragmented sleep. Deep rest may help the brain clean out toxic proteins, while research shows sleep deficiency is linked to Alzheimer's disease.
Mixed results with estrogen-only HRT
HRT for menopause comes in two main forms: treatments that include only estrogen, and combined therapies with both estrogen and progesterone. The treatment has a complicated history.
HRT was popular in the 1990s but fell out of favor after results from the Women's Health Initiative study were published in 2002. That study identified various risks tied to both estrogen-only and combined HRT options, some of which have since been overturned by newer data.
That said, the Women's Health Initiative study found that estrogen-only HRT came with an increased risk of endometrial cancers, and later analyses have backed up this idea. That's why today, clinical guidelines recommend that women who have not gotten a hysterectomy take combined HRT, while estrogen-only options are reserved for those who have had their uterus removed. (The added progesterone counteracts estrogen's thickening effect on the uterine lining.)
For the subset of women who take estrogen-only HRT, observational data published in August showed that this form of the treatment was linked to a reduced risk of dementia. The study, published in the journal Neurology, found that women who took estrogen-only HRT were less likely to show Alzheimer's-related changes in the brain than women who didn't take any HRT.
Laboratory data suggest that estrogen may help prevent the formation and accumulation of abnormal proteins that are related to Alzheimer's. (Image credit: KATERYNA KON/SCIENCE PHOTO LIBRARY via Getty Images)Estrogen-only HRT was also tied to better clinical outcomes: Treated women were less likely to be diagnosed with dementia, were less likely to show clinical and functional cognitive decline, and had better scores on memory tests, on average, compared with untreated women. These findings drew on two large, separate groups of older women, reporting data from 21,400 people in total, but they didn't include data on when each woman started HRT.
Whereas earlier studies of HRT and dementia risk relied on doctors' ratings of patients' symptoms, the Neurology study measured levels of Alzheimer's-related proteins in the brain after death. That's a more "definitive" marker of disease, said Bruno, a co-author of the study. However, the research was observational, so it can't say whether estrogen-only HRT directly causes the better brain outcomes the team observed, she stressed.
Although the Neurology study's findings are promising, they don't necessarily match the results of other studies of estrogen-only HRT and dementia. For example, a slightly larger observational study, published in 2023, found that estrogen-only HRT was associated with an increased dementia rate.
In that research, most of the women took a type of estrogen called estradiol, while Bruno's study included a greater variety of estrogens. That may have been the difference in the two studies' results, but teasing that out would require further study. Meanwhile, the conflicting findings muddy the waters of what estrogen-only HRT can do for brain health.
Does timing matter?
One big finding from the Women's Health Initiative study was that starting HRT — either estrogen-only or combined — after age 65 was associated with worse cognitive function and increased dementia risk, said Yuko Hara, director of aging and Alzheimer's prevention at the Alzheimer's Drug Discovery Foundation.
The same may not be true for people who start HRT earlier. For context, menopause starts around age 51 to 52, on average, and it's preceded by perimenopause, a transitional period when hormone levels begin to drop, typically around the mid-40s.
An observational study published in August in the journal Alzheimer's & Dementia found that starting HRT between ages 46 and 56 was linked to a reduced risk of dementia. That study did not differentiate between estrogen-only and combined treatment; it lumped all of the data together.
Patches (pictured) are one form of systemic HRT. They deliver hormones through the skin and into the bloodstream. (Image credit: SVPhilon via Getty Images)The protective link was especially strong in three groups: women with "surgical menopause," triggered by the removal of one or both ovaries; carriers of a certain variant of a gene called APOE that raises Alzheimer's risk; and women who had a relatively short time between their first period and menopause.
A 2024 meta-analysis of randomized controlled trials also found that HRT had a cognitive benefit for women with surgical menopause; that finding was tied mostly to estrogen-only therapies.
However, outside of that specific group, the idea of early HRT protecting brain health is far from settled.
Who might benefit, if anyone?
When it comes to using hormone replacement to protect brain health, the evidence isn't yet strong enough to recommend any kind of HRT as a way to protect the brain in all women, Hara said. Women who had one or both of their ovaries surgically removed are the exception to this rule.
"This is a distinct clinical population because the procedure can cause an abrupt, early loss of estrogen, rather than the gradual hormonal decline that occurs with natural menopause," Hara said.
For most women who have gone through natural menopause, "there is not enough evidence to recommend [HRT] specifically for preventing cognitive decline or dementia," she said.
HRT is not currently prescribed to prevent dementia — it is prescribed to ease menopause symptoms, such as hot flashes, night sweats and sleep disturbances. To settle the science on HRT and the brain, what's really needed is a well-designed clinical trial that follows women from perimenopause to postmenopause, Bruno said. That would reveal the effects of HRT on brain health and dementia risk more reliably than the studies done so far.
This article is for informational purposes only and is not meant to offer medical advice.
Help us improve Live Science Pro: We're always trying to make our content better. Leave us feedback about Pro here.
'> Does estrogen protect against dementia? And if so, who should take it?