The world’s largest iceberg, which had been grounded on the seafloor since the mid-1980s, is moving away from Antarctica and picking up speed. Now, scientists say the massive chunk of ice is drifting at a rate of three miles each day.

The movement appears to be a natural occurrence, and researchers haven’t found a specific inciting event that started the drifting.

“Over time, it’s probably just thinned slightly and got that little bit of extra buoyancy that’s allowed it to lift off the ocean floor and get pushed by ocean currents”.

Called A23a, the iceberg measures around 1,500 square miles—more than 20 times the size of Washington, D.C.—and it’s roughly 1,300 feet thick, making it two and one-third times the height of the Washington Monument. It weighs nearly one trillion metric tons.

“Icebergs this big can hang around for decades in one place, then one day decide to go for a ride. That’s when things get interesting.”

The iceberg has been moving faster in recent months and is now reaching the top of the Antarctic Peninsula. Scientists say it will probably head east, likely ending up on a path—called “iceberg alley”—that carries many icebergs from this region toward the South Atlantic.

Since it’s unusual for such a large iceberg to be on the move, scientists will follow it closely.

People are not at risk from A23a, though it may cause issues for wildlife if it runs aground in breeding areas. But melting icebergs can also benefit the ecosystem: They release mineral dust accumulated from Antarctica’s rock bed that serves as a source of nutrients for oceanic organisms.

While A23a’s breakaway from Antarctica in 1986 was likely a natural occurrence, climate change is causing the continent to lose ice, Marsh and Ella Gilbert, a climate modeler at the British Antarctic Survey, say to CNN. The National Snow and Ice Data Center announced in September that Antarctic sea ice reached its lowest annual maximum in recorded history this year.

“Climate change is causing the Antarctic Ice Sheet to lose mass at a significant rate,” says New Scientist.