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
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'