Volcanoes form where molten rock (magma), typically produced in the Earth’s mantle, rises to the surface. Volcanoes come in all different shapes and sizes which reflects their tectonic setting, the chemistry of the molten rock and how much dissolved gas is trapped within it.
“Where the magma is runny (low in silica) and there is relatively little gas dissolved in the magma, we see a lot of far-reaching lava flows that build up broad, gentle-sloped, shield volcanoes like in Hawaii. There are also a number of shield volcanoes in Australia,” says Honorary Associate Professor Heather Handley, one of the experts who assisted Australia Post’s philatelic researcher with the Australia’s Volcanic Past stamp issue, which will be released on 13 July 2021. Emeritus Professor Ray Cas from Monash University also assisted, as well as consultant Glenn Marshall.
“Where the magma is more viscous (higher in silica) and there is more gas dissolved within the magma we tend to get more explosive eruptions and the formation of steep-sided conical volcanoes, called stratovolcanoes, typically found in subduction zone settings, such as the ‘Ring of Fire’,” notes Heather.
“Maar volcanoes and scoria cone volcanoes are smaller volcanic features that occur where plates collide but also in the middle of tectonic plates. Maar volcanoes, such as the Blue Lake at Mount Gambier in South Australia and Lake Eacham in Queensland, form where magma interacts explosively with water such as groundwater aquifers. These explosions blast a deep hole in the ground that often fills with water afterwards. Scoria cones such as Mount Elephant form where the magma fragments into small pieces of rock that fall close to the vent and build up a loose cone of rubbly volcanic rock,” says Heather.
The last volcanic activity in Australia occurred around 5,000 years ago, with eruptions at Mount Gambier and Mount Schank, in South Australia. These produced a range of eruptions styles of varying explosiveness. The most explosive eruptions occurred when rising magma invaded aquifers or interacted with surface water with explosive consequences.
“Just think of hot cooking oil and cold water meeting and you’ll get the idea!” says Heather.
As a result, Australia has a wide diversity in volcanic landforms and features. The four volcanoes featured in the Australia’s Volcanic Past stamp issue capture this diversity and have some spectacular volcanic features.
Table Cape, in north-western Tasmania, is the large core of a substantially eroded volcano and what is seen today was likely once a lake of lava that filled the crater and then solidified. This process has created the striking flat land surface. Rising dramatically 170 metres from the sea, Table Cape last erupted around 12 million years ago.
Wollumbin Mount Warning, in the Tweed River Valley of New South Wales, is the central remaining “plug” of a vast eroded shield volcano, Tweed Volcano, which was active around 23 million years ago. Tweed Volcano is Australia’s largest central volcano, extending over 100 kilometres in diameter and likely reached over 2,000 metres above present-day sea level in its prime. Its heavily eroded present-day form gives us an extraordinary view into the inner structures and workings of this type of volcano.
Mount Elephant is a stunning volcanic scoria cone in the Newer Volcanics Province, in Victoria, rising around 200 metres above the surrounding lava plain. The crater rim of the volcano is lower on the north-eastern side of the volcano, resulting in a fantastic example of a breached crater. The breach in the rim was likely caused by the collapse or removal of a part of the rim by lava flowing in that direction.
Lord Howe Island, which lies in the Tasman Sea east of Port Macquarie in New South Wales, is the remnant of an extinct shield volcano that last erupted about seven million years ago. Ball’s Pyramid is a dramatic, jagged spire of eroded lava sticking out of the ocean, called a volcanic stack. It formed through the erosion of a shield volcano, and is part of the Lord Howe Seamount Chain, a long trail of volcanoes rising from the ocean floor along the eastern margin of Australia. At 562 metres above sea level, it’s labelled as the tallest volcanic stack in the world.
Heather Handley is a volcano scientist (volcanologist) who has been studying volcanoes for more than 20 years. Before coming to Australia in 2007, Heather completed a Geology degree (Bachelor of Science with Honours) at the University of Edinburgh, followed by a PhD on Indonesian volcanoes at Durham University, in the UK. Heather was awarded an Australian Research Council Future Fellowship from 2012 to 2018 to study the timescales of volcanic process and landscape evolution.
“I visited my first volcano when I was nine years old on a family holiday to Tenerife, a volcanic island off the west coast of Africa. I was awestruck at how this huge mountain capable of so much destruction looked so peaceful and quiet and wondered, ‘how do volcanoes work?’ This question has taken me all over the world to study volcanoes at some of the most active volcanoes on the planet,” says Heather.
Heather’s current roles include Honorary Associate Professor at Macquarie University; Science and Technology of Australia Superstar of STEM; and Governing Councillor of the Geological Society of Australia. Heather is also the Co-Founder and President of the Women in Earth and Environmental Science Australasia (WOMESSA). WOMEESA aims to create a unified network of women working in geoscience within academic, government and industry, to raise the visibility of women and provide role models.
“More than one billion people in the world are estimated to live within the range of direct impact of volcanic eruptions. Understanding more about how volcanoes work, for example, what triggers volcanic eruptions, how fast magma moves from its source to the surface, helps to reduce risk from volcanic hazards,” notes Heather.
An exciting research project Heather is currently working on is taking a microscopic look at Australia’s volcanoes.
“In the same way that tree rings can tell you about what the rainfall and temperature was like when a tree grew, the crystals within volcanic rocks hold clues to their journey through the Earth. I use x-rays and electron beams to uncover the secret histories of volcanic crystals, many of which are smaller than the thickness of a human hair,” says Heather.
“Through studying the spectacular shapes of volcanic crystals and their chemical patterns I will estimate the time it took for molten rock (magma) to travel from deep in the Earth’s mantle, from at least 30 to 40 kilometres beneath our feet, to the surface at some of Australia’s most recently active volcanoes. This will provide an estimate of the minimum eruption warning time of past eruptions. Preliminary results indicate that in at least at some volcanoes in southeast Australia it only took around two to three days for magma to reach the surface all the way from the upper mantle… that’s fast!” adds Heather.
There are ways for the general public to get more involved in the world of volcanoes too. As part of her research, Heather is surveying the general public on their opinion of volcanic hazards. In addition, the New South Wales government has recently launched a new “geotrail” around Warrumbungle volcano in New South Wales.
“There are self-drive and walking trail options and it’s a great way to get outdoors and learn more about Australia’s fiery past,” says Heather.
Heather is also very pleased to see volcanoes reach the public as a theme on Australian stamps:
“When you think of Australia, images of koalas and kangaroos, sun-drenched beaches and vast red landscapes probably come to your mind, but probably not volcanoes. Yet, there’s a vast tract, more than 4,000 kilometres in length, down the east coast of Australia that has been forged by volcanic fire more than tens of millions of years ago to just 5,000 years ago. I think it’s absolutely wonderful that Australia Post is raising awareness of Australia’s rich volcanic heritage and I hope that it will encourage people to find out more and hopefully visit a volcano.”
The Australia’s Volcanic Past stamp issue is available from 13 July 2021, online, at participating Post Offices and via mail order on 1800 331 794, while stocks last.
This content was produced at the time of the stamp issue release date and will not be updated.