They're call tabular icebergs, and they seem to be fairly common.
But in fact, there is little that is particularly unusual about the iceberg photographed floating near the Larsen C ice shelf in Antarctica, as sea ice specialist Alek Petty explains. He is a research scientist with NASA's Operation IceBridge, the group that took the stunning photo, and is based at the NASA Goddard Space Flight Center.
He says it's a kind of formation called a tabular iceberg, which forms in Antarctica, he says, "where we have these really wide floating ice shelves connected to land." The ice is "being kind of spread out in this very thin layer," Petty says, and "because it's ice and it's brittle, if that gets too weak or it comes into contact with something else, it can shatter and kind of break apart."
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Petty compares the process to a fingernail that grows and grows, "then it gets very weak because really that ice is being kind of extended out into the ocean," leaving less support for the floating ice. At that point, tides or strong winds could break icebergs off.
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But why such straight lines? Petty compares it to a glass plate that shatters — the lines are typically very straight. "You can just get these fracture lines that can form these interesting geometric structures," he says, and points out a different, triangle-shape iceberg spotted by NASA scientists recently.
- https://www.npr.org/2018/10/23/659799976...ar-iceberg