|Future of The World|
|This is a part of Future of The World: a collaborative project about our planet's future|
Today, Australia is a relatively un-volcanic place, with only 2, maybe 3 Holocene volcanic eruptions happening on the continent, all being relatively small scoria cone/shield volcano eruptions. But with the slow movement of the continent northwards, this hotspot is now centred just south of the modern island of Tasmania. Above this hotspot is a large volcanic island, composed of one very active volcano. The active volcano is a complex volcano, composed of a large shield volcano, with many cinder cones and small lava shields along its long summit rift zone. Most of its large eruptions are lava flows, many of which reach the sea.
The Barrenseed volcanic island, at the time it was 'discovered', was about half a million years old, with some old rocks up to one million years old. Although humans as a civilisation left Earth to colonise Mars, and eventually the rest of the solar system, before the year 3000, they continued to monitor the earth closely. Despite this, rather little was known about about Barrenseed Island before people first settled on it. The year that people first recolonised the earth was rather imaginatively named 'year one' A.H.R (A.H.R stands for 'After Humans Return'). Barrenseed Island was settled around 128 A.H.R, and it's first recorded eruption happened two years later.
Based on knowledge from other volcanoes, Barrenseed Island begun as a seamount on the outer continental shelf south of what is today the island of Tasmania. Within a relatively quick time of perhaps 100,000 years, it reached the surface, forming a smaller island, before going dormant. After several tens of millenia, it re-activated, and has remained that way ever since.
Barrenseed Island is a large shield volcano, roughly 40km by 30km in width, and largely covered by young lava flows. The volcano is primarily composed of low viscosity basaltic lava flows, though the formation of a shallow magma chamber has resulted in the evolution of the magma to form more silica rich lavas like andesite, which is abundant near the summit crater. Pyroclastic flow deposits are relatively rare, and on Barrenseed they usually occurs where a basaltic intrusion mixes with a pocket of evolved magma. One major pyroclastic flow has occurred since humans returned and started taking records.
Barrenseed island has an almost permanent snow cover above the 1100 meter elevation, though there are no true glaciers at presant. Prior two the heightened summit activity preceding the Vulcan Point Eruption, a small glacier existed in the summit crater, and had persisted through the previous eruptions, but the unusually hot lava of the volcano melted it prior to the massive flank eruption.
There have been four historical flank eruptions on Barrenseed Island, and many more summit eruptions. All the flank eruptions have followed after a period of sustained lava lake activity at the summit.
Fraser Peak Eruption, 132 A.H.REdit
Only two years after the first humans settled on Barrenseed Island, an eruption started at the summit. For a period of just under two years this lava lake rose steadily higher in the crater, before an earthquake swarm signaled an intrusion into the northwest rift zone. The summit lava lake rapidly sunk out of sight, and some several hours later an eruption started on the side of a large lava shield known as Fraser Peak, named after the first person to ascend the volcano. Lava erupted out of two parallell fissures on the northwest side of the mountain, and flowed as two lava flows into the ocean on the north coast of the volcano. Lava also erupted on the east flank of Fraser Peak, but the volume erupted was low and this lava never reached the ocean. The eruption lasted just under a month.
Barrenseed Point Eruption, 156-157 A.H.REdit
After the Fraser peak eruption ended, a vent at the bottom of the crater continued to glow, but by the next day all activity had ended. Then some 24 years later, lava erupted vigorously in the now deepened summit crater. Unlike the previous lava lake, this lava lake only lasted for 2 weeks, before a brief fissure eruption happened between the observatory and the summit crater. This vent didn't produce an extensive lava flow, but ponded in a depression. At the same time, another fissure erupted on the side of a steep slope next to the observatory, and fed a rapidly advancing lava flow for about four hours before shutting down when the lava flow had reached the 500 metre elevation. The next stage of the activity saw a massive outflow of lava on the outer flanks of the volcano near Barrenseed Point. This stage saw almost half a cubic kilometre of lava erupt over the course of two weeks, before the eruption slowed down to a trickle. Lava continued to erupt from the lowest vent of the fissure, and a lava tube formed, lava flowed into the sea in several places. The eruption lasted until well into the next year, a total of over 13 months.
Penguin Rocks Eruption, 197 A.H.REdit
The Penguin Rocks eruption started with the eruption of lava into the shallow summit crater formed after a prolonged summit eruption after the Barrenseed Point Eruption. Lava quickly overflowed the crater and flowed over the surface of the caldera, before lava drained out through a vent on the southern flank of the volcano. Lava streamed down into the sea near a large seabird colony, which included a penguin colony. For four days the lava gushed out of the flank vent directly into the ocean through an open channel. When the lava had cooled down enough, many of the penguins started to nest on the new lava.
Vulcan Point Eruption, 201 A.H.REdit
The Vulcan Point eruption started just four years after the Penguin Rocks eruption, and was the first eruption of the volcano in the second century A.H.R. The Penguin Rocks eruption didn't completely drain the lava lake at the summit, and within days of the flank vent becoming inactive the lava lake had returned. For some two years a lava lake existed in the filled summit crater, before it solidified over and activity became restricted to several small spatter cones in the crater. Then, after a further two years, a large earthquake swarm happened on the south flank of the volcano, and barely an hour later a fissure opened on the south flank. This initial eruption was very different to the previous quiet lava flows. The intrusion of basaltic magma mixed with a pocket of old evolved silicic magma within the volcano itself, which erupted first, and erupted violently. This first eruption sent a plume of ash to over 20 km high, and a large pyroclastic flow sped down the mountain into the sea. After this initial eruption, more traditional lava flows erupted from progressively lower elevation vents.
Within an hour of the eruption starting, the plinian eruptive cloud had spread out over the whole island and up to 100 km downwind, before the eruption changed character. Fluid basaltic lava began to erupt out of the original fissure, and out of a new second fissure about two km away. Lava reached the sea within hours of the eruption starting, as the initial blast had destroyed all the trees downslope of the vent. Later that night, a third fissure opened at a lower altitude, and the lava flows from the second and third vents combined on the coastal flat near the ocean. For the rest of the night this continued, but at around midday of the second day of the eruption, a very large earthquake occured as the intrusion broke into a large fault line near the coast. Shortly after, two more fissures erupted along this fault line, at the base of a steep slope, with the end of the fifth fissure less than 200 metres from the ocean. The initial fissures that opened the previous day continued to erupt, but at around evening of the second day activity at the 5th fissure rapidly increased, and the original vents stopped erupting lava and became inactive. Lava fountains along the fissure ranged from 20 to over 800 metres high, and lava quickly built the coastline out from the vent so that by the end of the week the coastline was over a km away from the vents, and for the first day of this surge an entire area up to 500 metres from the vent was incandescent at night anf flowing downslope. Fallout from the fountain often landed directly in the ocean. Activity declined from this first week, but continued at low levels for 17 months, or just less than 1.5 years. At the summit, the previously filled summit crater underwent a major collapse, and a new smaller caldera formed there.
Due to its characteristically un-Australian volcanic nature, the ecology of the Barrenseed massif is rather unique. Most trees are strongly resistant to burning, including the Barrenseed Gum, so called because its seeds are often found in areas swept clear of lava started fire, and because it is typically the first tree to start growing on a recently emplaced lava flow. This tree is found nowhere else in the world.
Active lava tubes are often filled to the brim with lava, but when the eruption stops or the lava is diverted to another course, the lava tube becomes inactive. Over timespans of up to several hundred years, they can become inhabited by cave dwelling animals. Lava tube fauna is relatively similar to that of other caves, but the volcanic and relatively ephemeral nature of the tubes makes them somewhat unique among caves.
Due to its location in the notoriously stormy southern ocean, Barrenseed Island is almost unreachable to animals that are unable to fly, and there are very few terrestrial mammals and reptiles. There is a large seabird colony, composed of familiar species such as gulls and petrels, with the enormous Aldrak, or Tasmanian Giant Albatross being a formidable sight. The strait below harbours seals, including kronoseals, dolphins and penguins, much like todays similar habitats. The apex terrestrial predator of the island is a 'giant' species of tiger beetle, known as Cincidela hephaestea, which, in the absense of competition, has grown to become the apex predator, and is able to hunt anything (save for human and and agressive adult seabirds.) on the island. Modern tiger beetles are often found in sandy areas, and the ashy soil of the island is an ideal habitat, allowing these beatles to grow to a whopping 11 cm long.