A magnitude-7.9 earthquake off the western Aleutian Islands shortly before 1 p.m. Monday triggered a tsunami warning over a wide area but generated only a small wave in one community, according to the National Tsunami Warning Center.
No reports of damage or injury related to the quake had been received by the Alaska Department of Homeland Security by 5 p.m. Monday, said department spokesperson Jeremy Zidek.
An initial tsunami warning for coastal areas from Nikolski to Attu, plus the Pribilof Islands to the north, was downgraded to an advisory a couple of hours after the 12:53 p.m. quake, and the advisory was canceled by 4:45 p.m., according to the NTWC.
The agency had advised people in the warning area to move to higher ground inland and to avoid the coast until local emergency officials indicated it was safe to return.
At 1:43 p.m., a small tsunami of just over half a foot was recorded at Amchitka.
At 2 p.m., Adak reported water leaving the harbor, the National Weather Service's Anchorage office wrote on Twitter, with residents there moving to higher ground.
In Adak, population roughly 325, tsunami warning sirens went off for "probably two to five minutes straight," said resident Vince Tutiakoff Jr. Residents climbed to higher ground, he said, and he was waiting for official word that it was safe to return lower ground on Monday afternoon.
The earthquake "was a good several minutes steady shake and roll, shake and roll, shake and roll," Tutiakoff said.
Still, "I've felt worse," said Tutiakoff, who has lived in Adak for more than 17 years.
The Alaska Volcano Observatory was monitoring seismic activity in the Aleutians following the earthquake to see if the tremor triggered "earthquake swarms," said Jeff Freymueller, coordinating scientist with the AVO.
While aftershocks occur within a certain distance -- in this case, "several tens of kilometers" -- earthquakes that occur outside that range are considered triggered events, he said.
Such was the case in 2004, Freymueller said, when an earthquake off the Indonesian island of Sumatra triggered seismicity at Mount Wrangell in Alaska -- about 6,800 miles away.
While it's "certainly possible that you could have (volcanic) activity triggered" by earthquake swarms, the AVO is monitoring the area mostly to avoid being "taken by surprise that we may see a change," Freymueller said.
On Monday afternoon, the AVO hadn't seen any indications of volcanic activity possibly due to the earthquake, he said.
Monday's earthquake struck at a depth of 62 miles, 15 miles northwest of Amchitka and 29 miles southeast of Little Sitkin Pass, according to the Alaska Earthquake Information Center. The U.S. Geological Survey initially listed the earthquake at a magnitude of 7.1, which was later revised to 8.0, then revised again to 7.9.
"The depth of this earthquake will limit the extent of tsunami danger," the updated tsunami warning said.
Natasha Ruppert, seismologist at the Alaska Earthquake Information Center, confirmed Monday afternoon that the magnitude was revised after information was received from the National Earthquake Information Center.
Aftershocks were occurring in the area Monday afternoon, she said. "We expect there will be quite a few," Ruppert said.
An aftershock of magnitude 6.0 struck the same area around 1:11 p.m., while a magnitude-5.9 quake followed at 1:30, according to the USGS. By 3 p.m., seven earthquakes of magnitude 3.7 or higher had occurred in the area.