BECKYHITCHIN
Wave of mutilation
SCUBA ’ s new science writer Becky Hitchin looks at the destructive force of tsunamis , and the role of the land ’ s natural defences
On 14 January 2022 , Hunga Tonga – Hunga Haʻapai , a submarine volcano in the Tongan archipelago , started erupting . It caused tsunamis not only in the Pacific islands of Tonga , Fiji , American Samoa , Vanuatu , but in many places along the Pacific rim , from New Zealand to Peru . In Tonga , the tsunami waves were up to 15m high .
In the case of Hunga Tonga-Hunga Ha ’ apai , an eruption caused the tsunami waves . But there are many volcanic processes that can cause tsunamis , and it ’ s not just eruptions . Both underwater and land-based explosions and shock waves can cause tsunamis , as can volcanic lava and debris flows hitting the ocean . In a large pyroclastic flow , up to a cubic kilometre or more of debris material can burn into the sea at high speed , displacing massive amounts of water away from the volcano . Earthquakes can also cause tsunamis , causing landslides and debris flows either above or below water , as can any type of above or below water collapse of a volcanic cone or caldera .
Impacts of tsunamis are wide ranging , and can affect whole ecosystems , whole coastlines , whole islands . While in deeper water , animals or plants may not even notice a tsunami wave passing , nearer the shore , the waves slow down , growing higher and forcing coastal water out to sea . Hence the eerie funnelling back of water away from the shoreline just before the tsunami waves hit .
When the tsunami wave actually crashes onto the shore , the force can be devastating for marine creatures as well as the habitats that sustain them . Fragile habitats such as reefs ( coral or otherwise ) can be completely levelled , and silt , sediment and waste deposited over the area . Mangroves and shallow-water seagrass beds , also critical
lead to inappropriate disposal methods , including air burning and open dumping , leading to secondary impacts on the environment .
There will also be longerterm contamination of the air , water and soil . Saltwater and waste may flow into inland water bodies , wells and aquifers , and cause local fields to salinize , potentially affecting agricultural yields for many years . In Sri Lanka , in the 2004 tsunami , an estimated 62,000 wells were contaminated by seawater , wastewater and sewage .
So how can we try and ameliorate this damage for future tsunamis ? There are many answers . Building
A massive volcanic eruption and tsunami hit Tonga in January new infrastructure with awareness of future events . habitat for many fish species and blue Better ocean observation systems to give carbon , can be destroyed . greater warning . But one thing that divers
On land , the initial problem is , of course , may want to think about is the role of healthy flooding and human health concerns coastal ecosystems like mangroves and caused by the impact of the tsunami waves . seagrasses . These work hard for us to lessen But the bigger problems lie ahead . Waves the impact , breaking the force of the waves , of that size and strength cause widespread trapping debris and preventing people from damage . Residential or industrial being washed out to sea . destruction will lead to vast quantities of Studies after the 2004 Sri Lanka tsunami wood , paper , concrete , cement , asbestos , showed that having just 30 trees per 100m2 bricks being distributed wherever the in a 100m wide belt may reduce tsunami waves touched . Domestic hazardous waste flow rate by as much as 90 %. This is , at may have also been compromised , and least , when these habitats still exist . In sewage , chemicals , fuel oils could spill . In many countries , mangrove habitat has the 2011 tsunami that hit Japan , we saw been extensively converted into shrimp what can happen , when 15-metre waves farms , tourist resorts and urban land , and hit the nuclear power plant at Fukushima . it is then that tsunami waves can force All three nuclear cores largely melted in the their way inland , destroying people , homes first three days after the tsunami hit . and livelihoods .
For small islands such as Tonga , there So next time you ’ re sitting on a tropical are further problems as their domestic beach , looking out to sea , a pina colada in services and disaster plans struggle to one hand and your dive log in the other , keep up with the realities of destruction . look around for mangrove habitats , ask the In particular , their waste processing dive resorts whether they are involved in systems are often overloaded trying to mangrove maintenance or restoration , look process the devastation the eruption for what remains to help protect you , and left behind . This rapid clean-up may also thank the mangroves . �
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