July 22, 2020 Tsunami: Shumagin Islands, AK, United States
A tsunami caused by a magnitude 7.8 earthquake began at Shumagin Islands, AK, United States on July 22, 2020 at 06:12:44 UTC. The water rose as high as 0.24 meters. Its effects were recorded at 13 places in at least 2 countries.
Where the waves reached
The source (white) and every runup with a place, colored by the water height recorded there. A ring is a runup NCEI marks doubtful.
- Under 1 m
- 1 to 3 m
- 3 to 10 m
- 10 to 30 m
- 30 m and more
- Height not recorded
Travel times
How long the first wave took to reach each part of the ocean, one line for each hour up to 24, estimated from the source and the depth of the sea.
The travel times are computed in your browser, which needs JavaScript.
- 1 to 4 hours
- 5 to 6 hours
- 7 to 14 hours
- 15 hours and more
Computed in your browser the way NOAA’s own travel time maps are: the wave travels at the square root of gravity times the depth, over NOAA’s ETOPO1 depths averaged to a 10 arc-minute grid. Checked against NOAA NCEI’s maps for 21 tsunamis over the first 24 hours, these lines fall within 10 minutes of NCEI’s at half the points compared and within 52 minutes at 9 in 10. They give when the first wave could arrive, not how high it is; bays, harbors and island chains finer than the grid can see it later. Not for use in a warning: see tsunami.gov.
The tsunami
- Date
- July 22, 2020, 06:12:44 UTC
- Source
- Shumagin Islands, AK, United States
- Cause
- Earthquake
- Earthquake
- Magnitude 7.8, 28 km deep
- Maximum water height
- 0.24 m (0.8 ft)
- Runups recorded
- 13
- Warning
- Local Tsunami Warning issued by a regional or national warning center
- Waters
- Ocean
- How certain
- Definite tsunami
- Source location
- 55.072° N, 158.596° W
The toll
- Damage
- Limited (under about $1 million) with the earthquake or eruption that caused it
Where the literature gives no number, NCEI records a description on a scale of 1 to 4, printed here in its words. Damage is in millions of US dollars of the year of the event, not adjusted for inflation.
What the record says
NCEI’s account, from the sources it cites.
The Shumagin gap is characterized by a broad continental shelf extending ∼150 km from shoreline, which is considerably wider than other world's major subduction systems. Based on our source modeling, we find that this unique feature was responsible for the extremely long-period tsunamis ranging between 40 and 90 min excited by the July 2020 Mw 7.8 Shumagin earthquake, which is unusual for an event of such a magnitude. The geometry of the continental shelf in this region translated a confined slip occurred at depths between 20 and 40 km on the plate interface into a significant portion of approximately 160 km coseismic displacements on the shallow submarine terrace with a mean water depth of ∼200 m. Consequently, such a setting and long-wave feature produced long-period tsunami waves. (reference #13148)
Our analysis of the July 2020 tsunami revealed that it involves very long period waves (51–64 min) which is unusual for an Mw7.8 earthquake. The tsunami coastal amplitude was small (~0.5 m) which is much smaller than that usually expected from a tsunamigenic earthquake of this size. (reference #13212)
Every runup
Nearest the source first. Heights are above sea level at the time; a tide gauge reads half the wave’s full height.
| Where | Country | Km from source | Water height, m | Inland, m | Measured by | First wave, UTC | Deaths |
|---|---|---|---|---|---|---|---|
| Sand Point, AK, AK | United States | 125 | 0.24 | Tide gauge (half the maximum wave height) | |||
| D46414 Bpr, SE of Chirikof Is, AK, AK | United States | 424 | 0.01 | Deep ocean gauge (half the maximum wave height) | |||
| Unalaska, Dutch Harbor, AK, AK | United States | 531 | 0.05 | Tide gauge (half the maximum wave height) | |||
| D46402 Bpr, S of Dutch Harbor, AK, AK | United States | 575 | 0.01 | Deep ocean gauge (half the maximum wave height) | |||
| D46409 Bpr, SE of Kodiak, AK, AK | United States | 643 | 0 | Deep ocean gauge (half the maximum wave height) | |||
| D46408 Bpr, Northwest Pacific Ocean, AK | United States | 977 | 0 | Deep ocean gauge (half the maximum wave height) | |||
| D46415 Bpr, SW of Juneau, AK, AK | United States | 1,240 | 0 | Deep ocean gauge (half the maximum wave height) | |||
| D46413 Bpr, East of Adak, AK, AK | United States | 1,353 | 0 | Deep ocean gauge (half the maximum wave height) | |||
| Henslung Cove, British Columbia, BC | Canada | 1,646 | 0.02 | Tide gauge (half the maximum wave height) | |||
| D21414 Bpr, Northwest Pacific Ocean, AK | United States | 1,718 | 0 | Deep ocean gauge (half the maximum wave height) | |||
| Tofino (Clayoquot),british Columbia, BC | Canada | 2,310 | 0.03 | Tide gauge (half the maximum wave height) | |||
| Ucluelet, British Columbia, BC | Canada | 2,344 | 0.03 | Tide gauge (half the maximum wave height) | |||
| Bamfield, British Columbia, BC | Canada | 2,377 | 0.02 | Tide gauge (half the maximum wave height) |
More
Every tsunami in 2020The 2000sTsunamis of United StatesThe earthquakeThis day in weather historyAlerts in force
Sources
Tsunami events and runups from NOAA’s National Centers for Environmental Information, Global Historical Hazard Database, cited as NCEI/WDS, doi:10.7289/V5PN93H7. Public domain. Read 2026-09-24. NCEI tsunami event 5753.