We have seen a frenzy of volcanic eruptions, and with these eruptions, we have seen the birth of new islands. A place that had once been sea is now land. Two volcanic islands recently born in the Red Sea have yielded stunning images, providing scientists with new insights about a little-known rift in Earth’s crust.
In the Red Sea between Africa and the Arabian Peninsula, there is a small chain of islands, owned by Yemen, called the Zubair Archipelago, with an interesting history. Just as Africa is slowly splitting apart along the volcanically active East African Rift, the Arabian Peninsula is breaking up with Africa along the Red Sea. In the 1700s and 1800s, the Zubair Archipelago hosted eruptions—the only recorded in the Red Sea—but they went quiet through the 20th century. In 2007, they woke up, with an eruption popping on one of the islands.
In 2011 and 2013, there were more eruptions, but this time they came from the seafloor and resulted in new islands. King Abdullah University of Science and Technology researchers Wenbin Xu, Joël Ruch, and Sigurjón Jónsson took advantage of satellite imagery and surface elevation measurements to observe their births.
The first eruption, at what is now called Sholan Island, was spotted by fishermen in mid-December 2011 and continued for nearly a month. It started as a long fissure, but soon narrowed to a single vent coughing up ash and chunks of rock as it broke through the surface of the water. When it was done, the island reached almost a hundred meters above the surface, with an area of a quarter square kilometer.
But the show didn’t end there. Some Yemeni scientists who visited the newborn island a few days later could see small landslides still moving rock around, and wind and wave reshaped the island over the next couple of months. The island’s shape even changed with the seasons after that, as seasonal cycles in the prevailing winds shifted a skirt of loose material to the northern or southern sides of the island. The crater in the center of the island even filled with seawater as it seeped through the permeable rock.
Video of the 2011 eruption forming Sholan Island. (Video by geologist Jamal Sholan.
The second island, called Jadid, surfaced in September 2013.
An ash cloud returned in late September 2013, just eight kilometers away from Sholan. This eruption lasted for almost two months and built a larger island called Jadid with a peak 186 meters above the surface and an area of about 0.7 square kilometers. The erosion of this island wasn’t as striking, but it also shrank very slightly over time.
The Red Sea is an enormous crack in the Earth’s crust called a rift, where the African and Arabian tectonic plates are tearing apart at about 0.4 inches (1 centimeter) per year. At a rift, the crust stretches apart slowly over centuries, like a piece of taffy candy, but it also sometimes suddenly splits when the strain becomes too great. For instance, in 2005, in nearby Afar, Ethiopia, giant fissures and fiery lava flows appeared in the rift zone after a series of earthquakes.
The new volcanic activity that formed these islands in the Red Sea could herald a rifting episode akin to that seen in Afar, said study co-author Sigurjón Jónsson, a geophysicist at the King Abdullah University of Science and Technology in Thuwal, Saudi Arabia.
“The segment of the plate boundary that goes on land in Afar has been looked at as the main boundary, but this new activity tells us the other branch in the Red Sea is still quite active,” Jónsson told Live Science. “We will have to follow it in the years to come and see how it continues.”
The chain of volcanic islands in the Zubair Archipelago marks another branch of the same rift zone, one that has been quiet for nearly 150 years. (Yemen’s Jabal al-Tair Island erupted in 2007, killing several people at a naval base.) [The 10 Biggest Volcanic Eruptions in History]
The two eruptions in the Red Sea were heralded by swarms of small earthquakes triggered by magma squeezing through long, narrow cracks in the Earth’s crust. The magma-filled cracks are called dykes, and are at least 6 miles (10 kilometers) long, the researchers reported Tuesday (May 26) in the journal Nature Communications. The islands are both less than 0.6 miles (1 km) wide.
Researchers Wenbin Xu and Joël Ruch, also of King Abdullah University, estimated the size of the dykes by measuring small changes in surface height as shown by satellite images snapped before and after the eruptions.
When the molten rock finally broke through to the seafloor, violent steam explosions tossed lava into the air. The tiny, sand-size lava fragments built up the islands. Over time, the fragments, called tuff, cemented into a hard rock similar to sandstone, Jónsson said. Waves have since eaten away about 30 percent of Sholan Island, the first to erupt.
Similar earthquake swarms have rattled the region for years, the researchers noted. The seismic shaking could mean that magma had been tunneling underground for up to a decade before the volcanic islands appeared, the researchers said.
“We may not be over this period of heightened activity,” Jónsson said. “If you look at all these swarms, we think the area was undergoing a rifting episode for a period of several years or more.”
The new islands are far from towns and villages, and are unlikely to disrupt air traffic with large ash explosions, Jónsson said. Ships traversing the Gulf of Suez could also easily divert around the islands, he said.
Using sensitive satellites that can detect subtle changes in surface elevations (a few centimeters or less) on the other islands, the researchers were also able to learn about things they couldn’t see in the photos. Faults, open fractures, and small motions on nearby islands showed what the magma had been doing below the surface of the eruptions. Long vertical sheets of magma called dikes, pointing roughly north-south and about ten kilometers long, had inflated and then escaped through the volcanoes.
It’s a little puzzling that these dikes weren’t quite parallel to the overall orientation of the Red Sea, but this is the kind of thing we see in rift zones. This rift zone may be pretty quiet, volcanically, but GPS measurements tell us the southern part of the Red Sea gets about six millimeters wider each year. And while there was a noticeable uptick in earthquakes preceding these eruptions, there has been consistent earthquake activity in that area for decades—an indication that magma has been busy moving around below the surface.
Because of all this, the researchers call the Zubair Archipelago “the surface expression of an active spreading segment that was previously under appreciated.” And that means we can expect that Sholan and Jadid islands are unlikely to be the last additions to the family.
Source: Live Science
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