A tsunami is a large ocean wave caused by a sudden movement of the seabed. Tremors reach the surface from the focus of an earthquake or the eruption of a volcano. Usually they are no more than a few tens of centimetres in height, however, they have long wavelengths of up to 100 km, and as they reach shallow water, they grow in height. Tsunamis may grow to between 15 and 30 metres high as they approach the coast, where they are sometimes known as tidal waves. Between 80-90% of all damaging tsunamis occur in the Pacific Ocean and the majority result from earthquakes. The eruptions in 1883 on the island of Krakatoa, which lies In the Sunda Straits between Sumatra and Java in Indonesia, caused one of the most devastating of all tsunamis. Waves were recorded as far away as the English Channel and San Francisco. The coasts in Java and Sumatra were struck by waves up to 42m high. 5-600 boats were sunk in the Straits and 36 000 perished in towns and villages on the coasts of the two islands. A more recent example is in 1993 a 30 metre high tsunami hit the south-west coast of Hokkaido following a nearby earthquake under the sea. The focus of the earthquake, measuring 7.8 on the Richter Scale, was only 34 km below the seabed. As a result the tsunami gathered speed rapidly and was travelling at an estimated 500 km per hour when it hit the small island of Okushiri. Damage to the island was extensive and resulted in the death of 158 people and destroyed over half the houses on the island. Its unlucky that the earthquake or volcano occurred in the first place, it is total coincidence that where a plate happens to meet underwater and cause tremors is enough to then go on and cause a tsunami which has the strength to cause a hazard to civilisation. If however there was no earthquake or volcano causing a tsunami to form then we wouldn’t need to even consider them occurring in the first place, without plate movement causing an earthquake we wouldn’t have tsunamis and then we wouldn’t have this type of hazard, a tsunami is a interdependent on either a volcano or earthquake. Also there is the factor of human life, if there was no people or property to consider how would we class it as a hazard, we wouldn’t be able to, if it had caused no harm it would have just stayed as an event, it is the whole just people being involved and present in an area which causes it to be a hazard.
Los Angeles with 13 million inhabitants has become known as ‘hazard city’. Not only does the San Andreas fault which crosses southern California create a conservative margin, but LA was built across numerous transform faults causing great earthquakes. The 1994 earthquake registered 6.4 on the Richter Scale killed 60 people and over 500 000 houses were left without power. Pacific ocean coastlines are particularly prone to tsunamis generated by submarine earthquakes or volcanic eruptions. The coastal fringes of Malibu to Redondo Beach are under the greatest threat. A sizeable tsunami generated by the sudden release of locked undersea faults could strike Los Angeles beaches with virtually no warning. Considerable residential development and most transport infrastructure would be damaged by such an event. Natural landslides occur within Los Angeles virtually every year and are most prevalent in the long winter months when there is lots of rain. Slumping and sliding of the hill slopes are largely the result of soft rocks such as unconsolidated gravel, sand and silt giving way, but also because of the steepness of the coastal cliffs. Floods have damaged LA on many occasions, flash flooding occur when intense winter rainstorms wash out debris from the canyons above the city which sweep away everything in front of them including homes, factories and roads. Due to having a Mediterranean climate is also suffers yearly droughts which is also associated with the bush fire problem that occurs. In 1970, 72 000ha of land was burnt, 295 houses destroyed and three people killed as the bush fires rages hill top properties in the Santa Monica Mountains. As just shown LA suffers lots of hazards, why is this you may ask yourself mainly due to the climate, being near the ocean and more so due to the huge plate boundaries generating the hazards. Many of the different events or hazards lead to other hazards i.e they are interlinked with one another for example 2 plates meet and cause an earthquake this then causes a landslide to occur. It is also bad luck and coincidental that LA is a warm region and so is more prone to drought, which then causes bush fires, but without the initial Mediterranean climate and temperatures this would never had occurred. LA is a big city with lots of inhabitants this is why when a hazard does occur it causes such devastation as it isn’t affecting a large area with few people but a large area with lots of people so they consequences will be more obvious.
New Zealand is classed as a high-risk country in terms of natural hazards. New Zealand is part of the Pacific Ring of Fire and is located on the Pacific and Australian crustal plates which is why it is subject to frequent earthquakes and occasional volcanic eruptions. Its eastern coasts look across to Chile and Peru, from whose vicinity tectonic activity may at any time trigger fast-traveling tsunamis. Landslips are also common in the steep geologically youthful New Zealand landscape, Mount Cook, New Zealand’s highest peak, lost 15m from its summit in the 1991 rock avalanche. Flooding is a risk to a maximum of 2.4 million people, volcanoes expose over 2 million and earthquakes expose 1.8 million people to risk. However return periods for volcanic eruptions are much longer than for earthquakes of comparable threat and while floods are very frequent they are rarely fatal.
Flooding, arising from high rainfalls, is often a major component of hurricane deaths and damage. Typhoon Thelma (November 1991) claimed 3000 lives in the Philippines, most drowned in flash floods triggered by the torrential rain. Landslides are equally dangerous in areas of high relief, tropical storm Bret (1993) had a death toll of 150, many of whom were buried in their hillside shanties by mudflows triggered by the torrential rain. On the other hand, low relief will make a region more vulnerable to storm surges, hurricane Audrey (1957) sent a 3.7m storm surge up to 40km inland through low-lying Louisiana in the USA. Tide timings may prevent or create catastrophes by reducing or increasing storm surges, hurricane Hugo hit South Carolina at high tide, increasing flood levels by 6m. These surges are worsened by wind-whipped waves up to 10m high. Coastal flooding can be the main killer in a hurricane, in 1970 a 6m storm tide killed 300 000 people in the Ganges delta region of Bangladesh.
People are increasingly living in areas where hazards can occur. Currently, 500 million people live on or near volcanoes. They live in these areas as the volcanic ash makes very fertile soil, which is good for growing crops which in turn brings in an income which supports their livelihood. Volcanoes are also very beautiful places and people enjoy living in view of them and they erupt pretty infrequently so feel there the benefits are greater than the risks. Some people are however are driven nearer to volcanoes as land is more sparse. The lower slopes of Mayon, Philippines are covered with rice fields and coconut plantations; tomatoes and other vegetables grow further uphill. Farming the soil of an active volcano is inherently risky. For poorer residents, however, it is often the only livelihood available. Mayon’s eruption in 1993 killed 75 people – all of them tomato farmers in the Bonga Valley, one of the ravines declared off-limits by the government. Today nearly 20,000 locals live and farm within Mayon’s Permanent Danger Zone. Humans put themselves at risk by living to close to it. If no civilisation was present near them, so when they do erupt nothing was damaged or hurt it couldn’t really be classed as a hazard but as an event. Only the presence of people living there and getting injured and loosing their houses and crops etc make it the hazard.
I feel that the majority of hazards are caused due to the presence of two plates meeting and causing formation of such things like earthquakes, volcanoes, hurricanes etc. Without regions and countries being present in these areas the hazards wouldn’t occur. Hazards tend to lead on from one thing to another as in an earthquake can cause tsunamis and warm hot weather may cause drought and fires. I have found that it is generally bad luck, coincidence and physical interdependence that mainly cause regions to have multiple hazards but also human factors play apart as without them it couldn’t be classed as a hazard.
