The Western Victorian Volcanic Plains
The Western Victorian Volcanic Plains are the third largest in the world and exceeded only by the Deccan in western India, and the Snake River Plateau in the United States ( Idaho-Nebraska ).
The Victorian Volcanic Plains are located in Western Victoria and covers over 2.3 million ha (10.36% of the State). It stretches from Portland in the west to Craigieburn in the east and from Clunes in the north to Colac in the south.
Climate and geology.
The Victorian Volcanic Plain bioregion is characterised by vast open areas of fertile plain covered with grasslands and grassy woodlands, and small patches of open woodland.
The bioregion is interspersed with stony rises and numerous extinct volcanic eruption points, denoting old lava flows and numerous scattered large shallow lakes and wetlands. Few major rivers cross the plain, the most significant of these include the Barwon, Hopkins, Leigh, Maribyrnong, Wannon and Werribee Rivers and Mount Emu Creek and their tributaries.
The basalt plain was formed by extensive volcanic activity mostly from the Upper Cainozoic era (Quaternary) from approximately 6 million years ago to as recently as 7,200 years ago at Mt. Napier. Several types of lava flows occurred including sheet flows and constricted flows along valleys.
Irregular and chaotic stony rises occupy large areas of the plains. Numerous volcanic cones dot the landscape with scoria cones being the most common (e.g. Mt Elephant, Mt Napier and Mt Noorat) although some basalt cones are present (e.g. Mt Cottrell).
Soils are generally shallow reddish-brown to black loams and clays (Conn 1993). They are fertile and high in available phosphorous.
Older flows in the Cressy and Hamilton areas have allowed a greater development of deep soils.
Dark saline soils occur around the margins of some lakes. Amongst the basalt are geological remnants that precede and survive the period of vulcanism that produced the “Plain”.
The majority of the elevation is below 250 m above sea level, however the maximum height does reach 720 m above sea level at two locations, Mount Doran and Mount Egerton, east of Ballarat.
Most of the region receives between 500 and 700 mm of rain per annum (Conn 1993) with rainfall distributed relatively evenly throughout the year except in the higher rainfall areas of the south west which receive a higher proportion of rainfall in winter.
The general pattern of climate is one of gradation rather than fluctuation. Average yearly rainfall generally decreases from southwest to northeast across the region.
Annual average rainfall figures are 840 mm for Portland, 720 for Colac, 680 for Hamilton, 630 at Skipton, 530 at Cressy and 450 at Eynesbury.
The warmest months are January and February with mean maximum temperatures ranging from about 20° to 27°C. In winter the mean maximum is as low as 10°C with a mean minimum of 3°C.
The above information was sourced from. View Link>
The information below was sourced from. View Link>
Lava Flows
Lava flows are the least hazardous of all processes in volcanic eruptions.
How far a lava flow travels depends on the flows temperature, silica content, extrusion rate, and slope of the land. A cold lava flow will not travel far and neither will one that has a high silica content. Such a flow would have a high viscosity (a high resistance to flow).
A basalt flow like those in Hawai'i have low silica contents and low viscosities so they can flow long distances. Such a flow can move as far away as 4 km from its source and have a thickness of 10 m (Bryant, 1991). These flows can move at rates of several kilometers per hour (Scott, 1989).
More silica-rich flows can move as far away as 1.3 km from their sources and have thicknesses of 100 m (Bryant, 1991). These flows can move at rates of a few to hundreds of meters per hour (Scott, 1989). If a lava flow is channelized or travels underground in a lava tube then the distance it travels is greatly extended.
The Rosette Rock
Lava flows as you can see don't move very fast so people rarely get killed by them. However, lava flows are very hot (between 550 degrees C and 1400 degrees C) and can therefore cause injuries. People have burnt their skin, charred their eyebrows, and melted the soles of their boots from being near or on a hot lava flow. Lava flows don't cool instantaneously. It can take days to years for a lava flow to completely cool.
7 Apr, 19:00, f = 50 mm from the mid lava field. An ephemeral vent on the top of its tumulus releases a double flow of pahoehoe lava during an exposure of 5 sec. Note the motion of the lava ropes.
Sourced picture from: View Link>
The biggest hazard of lava flows is that they destroy property. In the late 1980's, the town of Kalapana in Hawai'i was destroyed by lava flows. Lava flows buried cars and burnt homes, buildings, and vegetation. Electric power, water, and communications were cut off from the community.
Another hazard associated with lava flows (as well as other hot volcanic material) is they can melt snow and ice which can produce flooding. Melting of ice beneath a glacier may produce very large floods called jokulhlaups or glacier bursts (Bryant, 1991) Lava flows can also dam rivers which may in the future produce flooding if the dam were to break, though most lava flows are fairly porous (Scott, 1989).
The main concern with lava flows is how far they will ultimately extend. Equations have been used to estimate this distance (see Pinkerton and Wilson, 1994). But how do you stop a lava flow if you know it's heading toward your property? Different methods have been used including: breaching the sides of a lava tube or channel, diverting the flow, constructing barriers, and bombing the lava flow. Another way to stop a lava flow is to increase the lava flow's viscosity (Bryant, 1991 and Scott, 1989) by spraying it with water, increasing the rate at which gas escapes from the flow, stirring the flow, or seeding the flow with foreign nuclei (Bryant, 1991).
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