Could We Hear a Tsunami Coming?

Naomi Brown

Research published by Usami Kadri, a postdoctoral researcher at Cardiff University, has shown that a type of sound wave called an ‘acoustic gravity wave’ could be used to detect and possibly mitigate tsunamis. These waves are formed naturally with underwater earthquakes and landslides, as well as tsunamis.

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Image Credit: Flickr

What is an acoustic gravity wave?

A gravity wave is a wave generated in a liquid that is controlled by gravity, for example an ocean wave at the surface.  An acoustic wave, on the other hand, travels by longitudinal (lengthwise) compression.

One type of acoustic wave is a sound wave, which passes through a liquid by vibration, pushing against the particles in the fluid. Therefore, an acoustic gravity wave (AGW) is a combination of the two: a sound wave that spreads in the water layer and is governed by gravity.

Unlike surface waves, AGWs can span the entire water layer from the seafloor to the surface.  They can stretch tens to hundreds of kilometres and travel long distances in a very short time.

How could tsunami detection be improved?

Acoustic gravity waves travel at speeds close to the speed of sound in water – much faster than tsunamis. These waves also cause pressure disturbances on the seafloor, which makes them ideal for a tsunami detection system.

If two pressure sensors were placed on the seafloor in the deep ocean they could detect the acoustic gravity waves produced with an earthquake.  From this the epicentre, where the earthquake originated, could be located. Current systems detect the arrival of the tsunami so this idea could enable earlier detection.

In fact, the researcher, Usami Kadri, suggests that the Indian Earthquake in 2004 could have been detected over 3 minutes faster with AGWS. Even this could have saved many lives. He also demonstrated that by installing just 18 detection stations worldwide, all shorelines at high risk of tsunamis could be given an early alarm.

Could tsunamis be alleviated altogether?

When acoustic gravity waves interact with surface ocean waves they produce an exchange of energy. This can cause the surface ocean wave to decrease in height, also known as the amplitude, of the wave.

Kadri’s theory is that if two acoustic energy waves with carefully chosen amplitudes are emitted towards a long surface wave – a tsunami wave – there will be a distribution of energy between the three waves. This would cause the energy of the tsunami wave to dissipate.

If used against the Indian tsunami of 2004, it is predicted the height of the tsunami wave could have been decreased by 5 metres, which would have greatly reduced its impact.

Unfortunately, the technology to produce these huge, high-energy acoustic waves with good control over amplitude does not yet exist.  Therefore, the mitigation of tsunamis remains a theory at present. However, we can entertain the possibility that at some point in the future we may no longer have to face the devastation caused by tsunamis.

Bird Flu Is Back

Naomi Brown

Recently there have been numerous reports of the rapid spread of avian flu across Europe. With the memories of previous outbreaks that caused widespread devastation across poultry farms and fatalities in humans, there are concerns that this time it could be worse.

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Image Credit: Flickr

What is avian flu?

Avian flu is a type of influenza virus adapted to live in birds.  A virus is made up of genetic material, such as DNA or RNA, covered by a protective protein coat. Flu viruses are constantly changing, which means they have the ability adapt to become the best at infecting hosts. This is why they have the potential to cause pandemics (the spread of an infectious disease that has spread through human populations across a large region).   

Upon the discovery of the influenza virus the first parts to be identified were two proteins on the virus surface called hemagglutinin and neuraminidase. This lead the naming system still used today: ‘H’ for hemagglutinin and ‘N’ for neuraminidase. The types of virus were numbered as they were discovered, for example: the first virus identified was H1. However, there are six other genes present in flu viruses. This means that although strains have the same name, they have six genes that could be different. Therefore, it is possible that two viruses with the same name could either cause mild symptoms or be highly contagious.

It is worth noting that most types of avian flu do not infect humans. However, a number of the ones that do, cause serious infection. The strains of the virus that can cause fatalities in poultry are the H5 and H8.

The Last Outbreak

The current strain, H5N8, has evolved from H5N1, which was first recorded in a goose on a Chinese farm in 1996.  H5N1 is highly pathogenic, meaning it is contagious and so spreads quickly. This led to the rapid spread of the disease across Asia, Europe and Africa; hundreds of birds died, significantly impacting the poultry markets. The disease spread to humans from contact with these birds causing 452 deaths.

This Time

The H5N1 virus has had the opportunity to hybridise with other types of flu because the migrating birds congregate in North-Central Asia during the warm summer months before dispersing all over Africa, Europe and Asia.  This the first time that wild birds have died because this H5N8 strain has picked up new genes from flu in wild birds. There is a high likelihood of more H5N8 outbreaks in both wild bird populations – such as geese, ducks and gulls – and farmed animals, due to the migration of wild birds.

The first case of infection report in Europe was on a farm in Germany where there was swift response; a 3 km2 quarantine was set up and 30,000 chickens were culled. There have been further reports of infected birds from Austria, Lake Geneva in Switzerland and Romania.  

So far, no humans have been affected. A report from the World Health Organisation has concluded that the risk of human infection is low but cannot be excluded. H5 flu viruses rarely infect humans however one similar strain, H5N6, has caused 6 fatalities out of the 14 reported cases of infection in humans.  The disease has only been transmitted to humans when a person has come into contact with infected poultry, and there is no evidence that eating infected meat that has been cooked correctly can cause transfer of the disease.

If you’re worried about Avian flu, their advice is to avoid contact with dead or sick birds, wash your hands thoroughly after any contact with livestock and make sure to cook poultry thoroughly.