New Island Made of Tuff Stuff | Landsat

New Island Made of Tuff Stuff

In December 2014, a submarine volcano erupted violently in the South Pacific, sending superheated steam, ash, and rock 9 kilometers (30,000 feet) into the air. When the plume cleared and the ash settled in January 2015, a newborn island with a 120-meter (400-foot) summit was nestled between two older islands in the kingdom of Tonga.

Unofficially known as Hunga Tonga-Hunga Ha’apai, the newly formed island was expected to last for just a few months. It now appears to have a 6- to 30-year lease on life, according to a NASA-led study.

Though the volcano is quite remote, satellite imagery has given scientists an unprecedented opportunity to observe the formation, erosion, and evolution of “surtseyan” islands. Surtsey rose from the seafloor off of Iceland in 1963 during an explosive submarine eruption. Only a few such eruptions have occurred in the modern scientific era (the past 150 years), and the 2015 event in Tonga is the first to be extensively observed by satellites. Understanding the processes that build and erode such islands on Earth could provide insights on similar features on Mars.

Surtseyan events are distinguished by chemical reactions that alter fragile and easily eroded volcanic rock into a tougher material—literally called “tuff.” In these highly explosive eruptions, seawater becomes superheated as it mixes with magma. It then rapidly converts to steam, expanding and fragmenting the magma into fine grains of ash. The result is a mass of rock that is much more like concrete than typical volcanic rock.

Since the emergence of Hunga Tonga-Hunga Ha’apai above the water line in 2015, it has been tracked regularly through satellite observations by optical sensors and radar (which can penetrate cloud cover in the often-cloudy tropics). NASA scientists were first alerted to the eruption when it was observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA satellites. A team of researchers then requested regular measurements and high-resolution images by a combination of government and commercial satellites.

Researchers assembled that data into three-dimensional maps of the island’s topography, its changing coastlines and area, and the volume of rock and ash above sea level. The analysis was presented on December 11, 2017, at the fall meeting of American Geophysical Union.

“Volcanic islands are some of the simplest landforms to make,” said first author Jim Garvin, chief scientist of NASA’s Goddard Space Flight Center. “Our interest is to calculate how much the three-dimensional landscape changes over time, particularly its volume, which has only been measured a few times at other such islands. It is the first step to understanding erosion rates and processes and deciphering why the island has persisted longer than most people expected.”

The images above were acquired in April 2015 and September 2017 by the Operational Land Imager on the Landsat 8 satellite. The animation below is a composite of images from several satellites, and it shows the evolution of the island. Note how the shape of Hunga Tonga-Hunga Ha’apai flattens and becomes less round over the years. The isthmus, or land bridge, between the new island and Hunga Tonga (to the northeast) also grows wider.

https://www.youtube.com/watch?v=sIXyxvSEKFY

The team has calculated two scenarios for the future of the island. The first includes accelerated erosion by waves, which could destabilize the tuff cone in six to seven years, leaving only the land bridge between the two adjacent, older islands. The second scenario presumes a slower erosion rate and leaves the tuff cone intact for about 25 to 30 years.

The most dramatic changes to the island occurred in its first six months. “Those cliffs of volcanic ash are pretty unstable,” said remote sensing specialist and co-author Dan Slayback of NASA Goddard. In early May 2015, the Pacific Ocean washed over the southeastern rim of the interior crater wall, opening the crater lake to the ocean. At that point, both Garvin and Slayback thought the island might rapidly disappear. But by June 2015, a sandbar had formed and closed off the crater lake. While the island continued to evolve, it became more stable by late 2015. Wave action has slowly redistributed eroded sediment from receding cliffs on the southern side of the island, forming and shoring up the isthmus to Hunga Tonga.

The new island and its older neighbors are perched on the north rim of the caldera of a much larger underwater volcano. According to bathymetry measurements led by geologist and co-author Vicki Ferrini of the Lamont-Doherty Earth Observatory, the entire volcanic complex rises nearly 1,400 meters (4,593 feet) from the sea floor. Underwater, the base of the new volcanic dome extends about 1 kilometer (0.6 miles) from the shoreline into the floor of the larger caldera, which is about 5 kilometers (3 miles) across. In the shallows close to the southern side of island, the seafloor levels out into a nearly flat shelf, which may help explain the persistence of the new tuff cone and the redistribution for the eroded material.

Evidence of past eruptions from other, smaller domes are also apparent around the rim of the caldera, though few break the surface. “There’s a huge amount of material that came out from this eruption, possibly larger than at Surtsey,” said Ferrini. “The other interesting thing is that the two islands that surround this new land mass have some pretty tough substrate, so there’s something happening chemically to help make this solidify and stay in place.”

https://www.youtube.com/watch?v=Hds1OBxVg4s

Garvin and Ferrini and colleagues will continue to track the new island. They also hope to assemble a detailed chemical analysis of rock samples from the site.

The Tongan island could help researchers understand volcanic features on Mars that look similar. “Everything we learn about what we see on Mars is based on the experience of interpreting Earth phenomena,” Garvin said. “We think there were eruptions on Mars at a time when there were areas of persistent surface water. We may be able to use this new island and its evolution as a way of testing whether any of those represented an oceanic environment or ephemeral lake environment.”

NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey. Story by Ellen Gray, with Mike Carlowicz.

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https://landsat.visibleearth.nasa.gov/view.php?id=91412

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http://earthobservatory.nasa.gov/IOTD/view.php?id=91412&src=ve

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#satellite

Cape Horn: A Mariner’s Nightmare | Landsat

Cape Horn: A Mariner’s Nightmare

Before the opening of the Panama Canal in 1914, Cape Horn was a place that gave mariners nightmares. The waters off this rocky point, at the southern tip of Chile’s Tierra del Fuego peninsula, pose a perfect storm of hazards.

Southwest of Cape Horn, the ocean floor rises sharply from 4,020 meters (13,200 feet) to 100 meters (330 feet) within a few kilometers. This sharp difference, combined with the potent westerly winds that swirl around the Furious Fifties, pushes up massive waves with frightening regularity. Add in frigid water temperatures, rocky coastal shoals, and stray icebergs—which drift north from Antarctica across the Drake Passage—and it is easy to see why the area is known as a graveyard for ships.

On July 12, 2014, the Operational Land Imager (OLI) on Landsat 8 satellite captured this image of Cape Horn and the Wollaston and Hermite Islands.

Hundreds of ships have gone down near Cape Horn since Dutchman Willem Schouten, a navigator for the Dutch East India Company, first charted a course around the Horn in 1616. One vessel that narrowly escaped that fate was the HMS Beagle, with naturalist Charles Darwin aboard. In The Voyage of the Beagle, Darwin described the harrowing journey as the explorers tried to round the Horn just before Christmas 1832.

December 21st. — The Beagle got under way: and on the succeeding day, favored to an uncommon degree by a fine easterly breeze, we closed in with the Barnevelts, and running past Cape Deceit with its stony peaks, about three o'clock doubled the weather-beaten Cape Horn. The evening was calm and bright, and we enjoyed a fine view of the surrounding isles.

Cape Horn, however, demanded his tribute, and before night sent us a gale of wind directly in our teeth. We stood out to sea, and on the second day again made the land, when we saw on our weather-bow this notorious promontory in its proper form—veiled in a mist, and its dim outline surrounded by a storm of wind and water.

Great black clouds were rolling across the heavens, and squalls of rain, with hail, swept by us with such extreme violence, that the Captain determined to run into Wigwam Cove. This is a snug little harbor, not far from Cape Horn; and here, at Christmas-eve, we anchored in smooth water. The only thing which reminded us of the gale outside, was every now and then a puff from the mountains, which made the ship surge at her anchors.

NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.

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https://landsat.visibleearth.nasa.gov/view.php?id=91472

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http://earthobservatory.nasa.gov/IOTD/view.php?id=91472&src=ve

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Land Cover Map of France

From Landsat:

Land Cover Map of France

There are myriad ways to represent Earth’s surface: maps of roads, topography, or temperature all convey information about some aspect of the planet. Now, satellite-derived maps of land cover are becoming more detailed than ever and could help scientists gain insight into some key environmental questions.

“Earth’s surface changes very quickly, and having an accurate picture of it is essential,” said Jordi Inglada, a researcher at the Center for Space Studies of the Biosphere in Toulouse, France. “How many forests have been lost to urban settlements? Are lakes in a particular area drying out? Are coniferous forests disappearing in lower latitudes because of global warming?”

Visiting a remote research site is not always feasible. Even poring over dozens of satellite images on a computer screen can be tedious, Inglada noted. Maps of land cover have been updated infrequently because producing them traditionally required a person to manually find and select cloud-free satellite images. But Inglada and colleagues have found a way to fully automate the process, demonstrating that detailed maps can be generated quickly.

The map above is the result of the new, automated approach. This map combines data from all images of France acquired in 2014 by the Operational Land Imager (OLI) on the Landsat 8 satellite. A computer program first detects and removes artifacts such as clouds, and then a classification technique is applied to the remaining data to generate a map in less than 12 hours.

“The originality of our approach is that we use all available images during a year,” Inglada said. For Landsat, that means one image every 16 days, or 22 images per year for any place on Earth. Inglada’s method relies on this abundance of images to build up a time series for landscapes measuring 30 by 30 meters (the equivalent of one Landsat-8 pixel).

The evolution of the signal in each pixel—mainly information in the infrared, which is invisible to human eyes—allowed the researchers to distinguish types of surfaces that otherwise would be impossible to separate from one another. How the signal in each pixel changes over time carries an abundance of clues about which land surface type is contained in a pixel—much more information than can be learned by simply looking at the color of a pixel at a fixed point in time.

In this way, the scientists could differentiate between 17 different land cover types. Classifications include a range of artificial areas, including places where people have built up cities and transportation infrastructure. They could also distinguish between types of agricultural areas, and forested and semi-natural areas.

The second image shows a detailed view of the area around Nimes and Avignon. Artificial areas are shades of pink. Agricultural areas include annual summer crops (dark orange), which are mainly corn and sunflower; annual winter crops (yellow) are mainly wheat, barley, and rapeseed. The data can even differentiate between areas planted with fruit trees or shrubs (lavender) and vineyards (maroon).

“I can spend hours looking at the map,” Inglada said. “Seeing the Earth surface with this detail is impressive and shows the beauty of our planet.”

NASA Earth Observatory images by Joshua Stevens, using Landsat data courtesy of Inglada, Jordi, et al. (2017). Story by Kathryn Hansen.

Read More at:

https://landsat.visibleearth.nasa.gov/view.php?id=90751

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http://earthobservatory.nasa.gov/IOTD/view.php?id=90751&src=ve

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