Tsunami threat subsides in Victoria
Tsunami threat subsides in Victoria
On Saturday 15 January at 3.10pm the Hunga Tonga-Hunga Ha’apai volcano, located off the coast of Tonga, erupted with tsunami waves observed as a result.
Following the blast, a tsunami marine threat warning was issued for eastern parts of mainland Australia on Saturday evening including in Victoria for Lakes Entrance to east of Gabo Island, including the East Gippsland Coast as well as Macquarie Island. The tsunami warning was cancelled on Sunday, 16 January once the threat had passed.
The blast was one of the most explosive volcanic eruptions recorded in the 21st century, projecting a 30km ash column into the atmosphere. Within 30 minutes of the explosion, the eruption column was 350kms wide, producing a pressure wave that travelled around the world.
The wave was detected as far away as the United Kingdom, with tsunami waves up to 80cm recorded across the region from Japan to Chile.
On Sunday, the Bureau of Meteorology advised the cancellation of the tsunami warning for Victoria, with the larger and more dangerous tsunami waves no longer a threat, however small and unusual waves may still be expected.
#NSW, #LordHoweIsland, #NorfolkIsland #Tsunami Warnings for the marine environment continue after volcanic eruption near the TONGA ISLANDS yesterday. #TAS, #VIC and #QLD #Tsunami Warnings have been cancelled. Latest info here: https://t.co/Tynv3ZQpEq. pic.twitter.com/0ezTMMKQqZ— Bureau of Meteorology, Australia (@BOM_au) January 16, 2022
A tsunami is different from a wind-generated surface wave on the ocean. While wind-generated waves in deep water only cause water movement near the surface, the passage of a tsunami involves the movement of water from the surface to the seafloor.
Tsunami speed changes with the depth of the sea. An underwater earthquake at a depth of 5,000m can generate tsunami speeds of up to 800km/h. In most cases, as a tsunami travels closer to the coast, its speed and wave length may decrease, but its height may increase.
Accordingly, a significant tsunami can cause:
- Dangerous waves.
- Strong ocean currents and rips.
- Flooding in low-lying coastal areas, including coastal streams.
- Damage to marine facilities and boats.
- Extreme danger to low-lying coastal areas.
- Overtopping of foreshore dunes and sea walls.
- Flooding beyond the immediate foreshore.
- Damage to ports, marina and small boats.
- Damage to buildings and infrastructure near the shore.
- Extremely dangerous ocean conditions for hours or days.
Saturday’s eruption could be the first of many for the Hunga Tonga-Hunga Ha’apai volcano, which may produce further tsunami risks in the weeks and months to come.
As the control agency for tsunami emergency incidents in Victoria, the Victoria State Emergency Service assists with preparedness and response to the risk of tsunami which, in the worst case, could include evacuation, assisting with damaged buildings and search and rescue operations.
If you’re in coastal parts, it’s a timely reminder to pay attention to warnings on VicEmergency, download the app and take these steps if you are affected by warnings to any emergency:
In a marine threat tsunami, we advise:
- Get out of the water and move away from the immediate water's edge of harbours, coastal estuaries, rock platforms, and beaches.
- Boats in harbours, estuaries and in shallow coastal water should return to shore.
- Vessels already at sea should stay offshore in deep water until further advised.
- Do not go to the coast to watch the tsunami, as there is the possibility of dangerous, localised land inundation of the immediate foreshore.
- Check that your neighbours are aware of the situation.
For further information about what to do in a marine threat versus a land threat tsunami is available on the VICSES website here.
VICSES sends its best wishes to Victoria’s Tongan community, as they wait to hear news from their friends and relatives in Tonga.