IN 1964 I came across a copy of the journal ‘Scientific American’ which contained an inspiring article by Canadian geophysicist Tuzo Wilson. Wilson transformed scientific knowledge and understanding of volcanoes, ocean trenches, fold-mountains, and earthquakes by viewing Earth as a series of moving plates.
He highlighted the fact that the vast majority of volcanoes are found at plate boundaries apart from a few places such as Hawaii in the North Pacific Ocean and a string of islands running north to south along the Mid Atlantic Ridge from Ascension Island to Tristan da Cunha. Hawaii is known as a volcanic hotspot, which is over 3,200km from its nearest plate boundaries along the so-called ‘Pacific Ring of Fire’.
The Earth consists of a series of layers: the centre or core is made of nickel- iron: the Nife layer radiating tremendous heat. Beyond this lies the Mantle, which is in a semi-liquid state. Floating on the surface of the Mantle is the Lithosphere or crust, composed of denser silica-magnesium (Sima) oceanic plates and less dense silica-aluminium (Sial) continental plates. As the mantle is warmed from the core below, so convection currents rise to the surface and spread out before cooling and descending.
These convection cells move the plates around and towards or away from each other. Such rising currents of molten magma are referred to as ‘plumes’ which, upon breaking through the crust and meeting the seabed, disgorge molten magma in the form of volcanic lava.
In the fullness of time, volcanic islands are built up and such an island is Big Island, Hawaii, which today has five active volcanoes. There, the movement of the Pacific Oceanic Plate carries the volcanoes that have breached the surface of the lithosphere with it. Thus it is possible, assuming that the position of the volcanic plume remains relatively stable, to measure the age of the volcanoes and undersea mountains according to the rate of plate movement together with the use of argon and potassium radioactive isotopes.
As the lava from the volcanic plume cools, so minute particles of iron (magnetite) align themselves in the current direction of the Earth’s magnetic field. Geophysicists such as Wilson have thus been able to determine the latitudes at which each volcanic island formed by simply measuring the orientation of the grains of magnetite.
It has been found that the Hawaiian hotspot has drifted southwards during its geological history as the seafloor has been stretched as the plate spreads. Today, these ‘drifting’ volcanoes to the northwest of the hotspot move at a rate of between five and 10 centimetres a year.
Goddess of Fire
Early Hawaiian cultures noted that the Hawaiian Islands to the northwest were older than those to the southeast. This was based on their observations in differences in erosion rates and the depth of their soils.
Local legend supports scientific evidence. Folklore recalls that Pele, the Goddess of Fire, was born to Hina, who descended from Mother Earth and Father Sky. Pele seduced her older sister’s husband and, upon being attacked by her sister, fled to an island in the southeast of the Hawaiian chain. Chased by her sister from island to island, Pele finally took refuge in the Halemaumau crater of the volcano Kilauea, standing today at 1,247 metres above sea level, on Big Island. Perhaps with Kilauea’s recent violent eruption her sister has caught up with Pele again.
Volcanic lava flows
For many a year volcanologists have used Hawaiian terms to describe two specific types of lava according to what they look like and behave in their outpourings. Slow moving lava, because of its low viscosity, is referred to as ;pahoehoe’ (meaning smooth, unbroken lava) and looks like rope coils. Sometimes it is called ropey lava. Rapidly moving lava is called ‘aa’ (meaning stony, rough lava) with a fast heat loss and its increase in viscosity causes it to appear as jagged angular blocks. Aa tends to flow when a volcano becomes more explosive and ejects large chunks of lava skywards.
During the 20th century, Kilauea experienced a huge eruption in 1923 to 1924, when lava covered vast areas but at that time Hawaii was not as populated as today. Subsequent eruptions occurred in 1955, 1960, and 1975. Since 1983, Kilauea has continuously erupted through a minor volcanic cone Puu Oo. The recent events, which began with tremors and in earnest on May 4, have literally been earthshattering.
Essentially there have been a series of rift or fissure eruptions on its slopes as well as emissions of boiling hot lava over the crater rim. The fissure eruptions and activity within the crater have been superbly documented from above and at ground level as the lava flows advance creating freeway-like paths of basalt. It was a magnitude 6.9 earthquake, which occurred at 12.32pm local time on that fateful Friday on the southern slopes of the volcano (at almost the same spot as in the 1975 magnitude 7.1 earthquake) that triggered the recent events. In the 1975 eruption, two people died from toxic gas inhalation and 28 were injured. In this present eruption, the crater floor of Puu Oo has collapsed.
Currently lava fountains of pahoehoe are spouting 70 metres into the air with hazardous levels of sulphur dioxide producing poor air quality. Changes in wind directions are affecting residents and 10 days after the initial eruption, Kilauea spewed volcanic ash 9km into the atmosphere, threatening jet aircrafts’ turbines with fine glass particles as the ash cooled. A day before ‘ballistic blocks’ of lava (or pyroclasts), the size of refrigerators, fell out of the sky crushing one person’s leg. Already mass evacuation of homes, school closures, the isolation of some residential areas, roads blocked, and power lines down are the direct result of the lava surges.
Water mains have been shattered, and a geothermal electricity power plant overcome. ‘Vog’ or volcanic smog and ‘laze’ – lava haze – fills the air as steam and sulphur dioxide belch forth as the lava flows into the sea and reacts with the saltwater.
Upon entering the sea, the lava cools and piles up in pillow-like form to create a third lava type, pillow lava, and thus slowly the land area of Hawaii is extending seawards. For the 200,000 inhabitants of Big Island, although used to living alongside Kilauea’s eruptions, life has become a nightmare since the beginning of May.
At the time of writing, the US Geological Survey researchers at their Hawaiian observatory predict that yet more is to come and fear a massive explosive eruption of Kilauea, which could well send ash even higher into the atmosphere disrupting world air flight paths for some time. As with all natural events, output ceases when input declines and in Kilauea’s case, when the plume has exhausted its present magma input, its lava outpourings will cease but in the meantime a lunar-like landscape is being created on huge sections of Big Island. I await the outcome with bated breath.