29 | August | 2018 | Kevin's Walk on the Wild Side

File 20180827 149487 1nrw8d2.png?ixlib=rb 1.1 — Detail of a fish (likely black bream) on Enderby Island.
Photo Vic Anderson

Jo McDonald, University of Western Australia

The West Australian government has committed to pursuing a World Heritage listing for the rock art of Murujuga. Murujuga is the Aboriginal name for the Dampier Archipelago and the Burrup Peninsula in north west WA and is home to at least a million individual works of art.

Australia has some of the world’s richest and most diverse rock art. While rock art is found all around the globe, Australia is relatively unique because here there are still cultural connections between rock art and the people who created it.

At present, Australia has only three cultural World Heritage sites (of which only one – Kakadu – is listed for rock art). In contrast, France has over 30 World Heritage-listed rock art sites.

I and my colleague Peter Veth have argued that Murujuga rock art meets three criteria for outstanding universal value: because of the creative genius and skill of the artwork; the extraordinarily old and continuous engraving tradition; and the combined cultural landscapes of the area, including quarries, living sites, and shell middens.

These illustrate significant transitions in human history in the face of major changes in sea level and surrounding environment.

The boulders of Murujuga are home to more than a million works of rock art.
Shutterstock.com

Animals no longer found

When people first started using this landscape 50,000 years ago, it was located around 100 km from the coast. It was wetter and warmer than it is now – and the archaeological record of the coastal plain at this time demonstrates an entire group of animals no longer found in this part of Australia. Murujuga’s artists painted some of these animals, such as crocodiles.

Then, during the last ice age (between 30,000 and 18,000 years ago), the coastline was even further away (160 km). People were were living in the Murujuga Ranges at this time. There are a number of paintings of animals that are now extinct, such as thylacines and a fat-tailed species of kangaroo, which testify to the changing environment.

Speared fat-tailed kangaroo positioned on irregular boulder; Dolphin Island.
Photo J. McDonald.

Then, as the ice caps melted and the sea level rose, people became more concentrated on the new coastal landscape. Recent studies across the archipelago have demonstrated the scientific significance of the outer and inner islands of this cultural land and seascape.

Dugong, turtles and fish

Around 8,000 years ago, people began to construct houses. Art production at this time was in full swing. The most recent rock art includes dugong, turtles, fish as well as the small rock wallabies and quolls that now live on the islands.

Fish depiction (likely black bream), Enderby Island.
Photo Sarah de Koning.

As well as houses there are myriad stone arrangements, standing stones and terraces. This is a monumental hunter-gatherer-fisherperson landscape, which rivals the period in Europe when people were constructing stone monuments such as Stonehenge (except in Europe this occurred thousands of years later).

The artworks in Murujuga were made on the rocks using stone tools. Together they show how people have been living in the region for thousands of years, first as hunter-gatherers, and later with a focus on fishing.

Contemporary traditons

This rock art is still associated with contemporary traditions, ideas, and belief systems of traditional custodians. It is the widely-held belief that many Murujuga engravings represent and embody ancestral beings (Marga), while some of the standing stones are thalu sites, critical for the regeneration of key species such as a range of fish, birds and kangaroo, and even sandflies.

Five local Aboriginal groups hold native title in lands next to the archipelago – the Ngarluma, Yindjibarndi, Yaburara, Mardudhunera and Wong-gg-tt-too. Together, they are represented by Murujuga Aboriginal Corporation, which jointly manages Murujuga National Park with the WA state government. The peninsula and the islands are also listed as having National Heritage values. This listing excludes parts of the peninsula that have been previously damaged by industry.

Pelican, Murujuga.
Photo Sarah de Koning.

National Heritage listing paves the way for Murujuga to become a World Heritage site. Recently, traditional custodians and others came together for a summit in Karratha and concluded resoundingly that World Heritage listing would be appropriate for Murujuga, and that it would help protect this extraordinary place.

Author Tim Winton also joined the push for World Heritage status.

Yesterday’s announcement is a significant moment for WA – which doesn’t have any Aboriginal cultural sites listed as World Heritage. And for the traditional custodians, it is the next step in their quest for recognition and greater protection of this place’s special significance.

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Placing Murujuga on the Tentative List is the beginning of the formal process to achieve World Heritage status. This will still take several years, but as the CEO of the Murujuga Aboriginal Corporation, Peter Jeffries, said yesterday, the traditional owners are now driving the process.

Jo McDonald, Director, Centre for Rock Art Research + Management, University of Western Australia

This article was originally published on The Conversation. Read the original article.

Heather Handley, Macquarie University; Jozua van Otterloo, Monash University, and Ray Cas, Monash University

Spectacular images of recent volcanic eruptions in Hawaii are a little disheartening – especially given news reports suggesting there is a sleeping volcano under Melbourne that could awaken and erupt at any moment.

Understanding the geological differences between Melbourne and Hawaii is really helpful in working out how we can keep an eye on future risks in Australia.

The Newer Volcanics Province

Victoria and South Australia do host an active volcanic field, called the Newer Volcanics Province (NVP). This is not a single volcano with a large single chamber of molten rock (magma) — the common image of a volcano — but a widespread field of multiple small volcanoes, each with a small volume of magma.

Melbourne lies at the eastern end of the NVP, and the most recent eruptions in this area occurred over a million years ago.

Mt Gambier in southeastern South Australia represents the western margin of the volcanic field and the most recent eruption — only 5,000 years ago.

Between Melbourne and Mt Gambier there are more than 400 small volcanoes that erupted over a period of 6 million years.

The NVP was most active between 4.5 million to 5,000 years ago and volcanologists consider the field to still be “active” with the potential for future eruptions.

We do not know when the next eruption will take place.

Volcanoes of the Newer Volcanics Province (a) Mt Napier, SE of Hamilton (b) The Noorat complex (c) The Mt Gambier Volcanic Complex, near Mt Gambier (d) The Mt Schank Volcanic Complex, near Mt Gambier (e) Purrumbete volcano, near Camperdown (f ) Tower Hill volcano, near Warrnambool (g) The Red Rock Volcanic Complex, near Colac.
Ray Cas and co authors

The NVP is located within a tectonic plate – and not along a plate edge like the Ring of Fire volcanoes (for example, Mt Agung on Bali).

Tectonic plates are large slabs of rock made up of the Earth’s crust and uppermost part of the mantle (the lithosphere) which form the outer shell of the Earth, and move around slowly relative to each other.

Volcanoes act in different ways

While Kilauea volcano in Hawaii is also located within a tectonic plate, it has several key differences with the NVP in Southeastern Australia.

Magma source and volume

While Hawaii sources large volumes of magma from deep within the Earth, the NVP only receives small amounts of magma from just below the Earth’s crust.

It’s worth noting here that the makeup of the magma is similar in both locations, with both erupting runny basalt – a type of rock low in silica, and high in iron and magnesium.

We suspect that in Australia’s NVP, magma can move very fast from its source to the surface (on a time scale of days). This can bring rock fragments of the mantle (xenoliths) to the surface as the magma moves too fast for them to melt.

Fragments of the mantle (xenoliths) in a volcanic bomb erupted at Mt Noorat, brought to the surface by ascending magma.
Ray Cas

Eruption frequency

Hawaiian volcanoes can erupt numerous times, but NVP volcanoes are largely monogenetic — that is, each only erupt once or over a restricted period of time.

Crust thickness

Hawaii is located on the oceanic crust of the Pacific Tectonic Plate, which is a thin (around 7 km) layer of material that is dense and rich in iron. The magma can rise through this crust quite easily.

In contrast, the NVP is located on continental crust which is much thicker (about 30km), richer in silica and much less dense. Magma finds it much harder to travel through this kind of material.

Water adds danger

The explosivity of a volcanic eruption can depend on availability of water.

“Dry” eruptions – where magma has little-to-no interaction with ground water or water on the Earth’s surface – typically produces mildly explosive eruptions such as lava fire fountains, showers of lava fragments and lava flows.

The most explosive, hazardous eruptions form where rising magma interacts with ground water, surface water or sea water. These “wet”, (phreatomagmatic) eruptions can produce deadly, fast moving, ground-hugging currents of gas and volcanic material – called pyroclastic surges, and send abundant fine volcanic ash into the atmosphere.

The Australian Mt Gambier eruption 5,000 years ago was a “wet” eruption, and had a volcanic explosivity index of 4 on a scale of 0-8 (where 0 represents a lava eruption, 1 a spectacular lava “fire” fountain as recently witnessed in Hawaii, and 8 represents a catastrophic explosive super-eruption).

The accompanying ash column is estimated to have reached 5km to 10km into the atmosphere.

On Hawaii explosive eruptions are rarer because the magma has a low gas content and groundwater aquifers are not as large as in the NVP. However, when lava flows into the sea there are often phreatic or steam explosions which can be hazardous to nearby spectators.

Mt Gambier’s Blue Lake was created by a huge volcanic eruption.
from www.shutterstock.com

There’s a lot we don’t know

Another important factor relates to how we keep an eye on volcano risk at the two sites. Kilauea on Hawaii is extremely well monitored, and tracking magma moving underground has helped predict eruptions.

In contrast, the NVP is less well monitored, likely because there is no present volcanic activity, and it’s a huge region.

However, warning signs of an eruption are likely to be similar in the NVP to those on Hawaii – small earthquakes, minor uplift and/or subsidence of the ground, changes in ground temperature and gas or steam rising out of the ground.

Also, based on present knowledge of the NVP, there is no clear eruption pattern we can use to try to predict when or where the next eruption will be.

If the NVP were to erupt, significant impacts on our lives would likely occur. These may include:

the closure of surrounding roads by lava flows and ash fallout
volcanic ash and rocks loading roofs of local buildings
contamination of water reservoirs by ash
damage to machinery and electricity infrastructure by infiltrating ash
respiratory problems for people prone to asthma, and
disruption to air traffic across southeastern Australia due to drifting ash clouds driven by prevailing south-westerly winds.

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Further scientific research is required on active volcanic fields such as the NVP to know how fast magma travels from its source to the surface, how much warning we might have before an eruption, and how long an eruption and its impacts might last.

Heather Handley, Associate Professor in Volcanology and Geochemistry, Macquarie University; Jozua van Otterloo, Assistant Lecturer in Volcanology, Monash University, and Ray Cas, Professor emeritus, Monash University

This article was originally published on The Conversation. Read the original article.

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Kevin's Walk on the Wild Side

Environment, Wildlife and Wilderness – Articles and News

Daily Archives for August 29, 2018

Explainer: why the rock art of Murujuga deserves World Heritage status

Animals no longer found

Dugong, turtles and fish

Contemporary traditons

Would an eruption in Melbourne really match Hawaii’s volcanoes? Here’s the evidence

The Newer Volcanics Province