Unsuspectingly lurking next to the massive metropolis of Melbourne, Australia, is a region of young and active volcanoes! This volcanic province covers an area >23,000 km in the southern state of Victoria. The volcanoes here are dormant, but still active, with the last eruption ~5000 years ago at Mt. Gambier. The landscape is flat due to extensive plains of basalt, but it is riddled with features like volcanic scoria cones, maars, shield volcanoes, etc. I recently jumped on the opportunity to head across the water from Tassie to check out some of these stunning and ideal landforms on a trip lead by Dr. David Cooke and Dr. Rebecca Carey from our geology department at the University of Tasmania. Hopefully in this blog post I can share my travels to some of these young volcanic features and show what they look like and how they formed.
Violent volcanic products
The young, volcanically active region of Victoria is known as an intra-plate continental volcanic province. While it still is a bit of an enigma what causes this type of regional volcanic activity, volcanism is thought to be from intra-plate varying convection currents between the underlying lithosphere and asthenosphere (Davies and Rawlinson, 2014). There are over 100 eruption centres, and their products are from mafic-dominant (i.e. basaltic) effusive and explosive eruptions.
Effusive eruptions produce lava flows and domes from outpouring of low volatile (i.e. degassed) magma.
Explosive eruptions produce pyroclastic deposits and are volatile driven.
Southern Victoria has some uncommon example of effusive eruption products. Heading southwest along the Great Ocean Road we stopped at Airey’s Inlet on the coast to check some of these unusual features out. The basalt at Airey’s Inlet has interesting contact with an overlying limestone layer… When lava intrudes into wet, unconsolidated sediment it gets quenched rapidly, producing fluidal edges in a texture known as “peperite” (McPhie et al., 1993). This process is debatably what happened ~25 Ma at Airey’s Inlet (Cas et al., 1994).
The other eruption style mentioned above is explosive, and these usually generate buoyant plumes that result in pyroclastic fall, flow and surge deposits. They are three main types of explosive eruptions with vary due to the amount of water interaction:
1) magmatic (no external water, magmatic volatiles)
2) phreatomagmatic (magma and external water)
3) phreatic (water without direct magma contact)
Both Mt. Noorat and Mt. Eccles are volcanic complexes (i.e. tuff rings and scoria cones) with examples of combined magmatic and phreatomagmatic fall (± surge) deposits. Ash-rich phreatomagmatic layers are interbedded with scoria-rich magmatic layers that drape and mantle the topography (a signature of fall-deposits). While it is not as simple as this, or true in all areas, the scoria-rich layers may represented a drier magmatic explosive stage, whereas the intermittent ash and lapilli layers may represent a ‘wetter’ phreatomagmatic explosive stages. Within these fall deposits are scoriacious volcanic blocks and bombs (e.g. Mt. Noorat). Within some of these bombs are olivine-rich mantle xenoliths, so the eruptions may have been so violent that they entrained bits of the mantle!
Lastly, my favorite volcanic deposit (possibly because of their common association with magmatic-hydrothermal ore deposits) are maars-diatreme complexes. Maar-diatreme complexes form from extremely violent phreatomagmatic and phreatic explosions. This results in a maar (i.e. a circular volcanic crater surrounded by low aspect ratio, outward-dipping rims of phreatomagmatic base-surge and fallout deposits) and an underlying diatreme (i.e. a downward-tapering cone-shaped breccia body filled by volcaniclastic debris and collapsed wall rocks).
The characteristic circular maar craters are beautifully exposure from the air in southern Victoria, and examples include Lake Purumbete, Lake Bullen Merri, and Tower Hill. Both Lake Purumbete and Tower Hill are ideal location to check out what maar rims look like in outcrop. High-energy ash- and lapilli-sized surge deposits with cross-beds are present at both Tower Hill and Lake Purumbete, within the gently-dipping maar rim layers.
Tower Hill had a late volcanic phase of nested scoria cones grow in the centre, and thus the maar rim deposits here have intermixed ‘dry’ basaltic scoria and ‘wet’ ash deposits. Also… Tower Hill is a great spot to see Australian wildlife, like koalas and emus!
Final thoughts
Not only is it geologically interesting, southern Victoria is a lovely place to visit. A common way of traveling is along The Great Ocean Road, a famous stretch of road that takes you past some of the places we stayed, like Port Fairy, and to other stunning landmarks like the Twelve Apostles…
…though don’t have your hopes up if you want to see all dozen apostles, as though yes, they are very spectacular sea stacks of eroded layers of and hard limestone, due to extensive coastal exposure and erosion there isn’t exactly twelve anymore.
Although it’s a lot more complicated than what I describe in this blog post, there is still heaps to learn and see in southern Victoria on young volcanic deposits.
-Stephanie
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Wow! Thank you for so much interesting information! I have lived in Victoria most of my life but only just realized how many volcanoes are here and that there are so many different types! Thanks for introducing me to yet another amazing and stunning side of Mother Nature!
[…] Cross section of cinder cone of Mount Eccles. Note the bedded layers. Image courtesy Stephanie Sykora Exploring the Earth blog, 2015. http://exploringtheearth.com/2015/01/06/volcanovictoria/ […]
Steph, you may find this may answer a few of your questions about WHY some volcanic sediments are formed,
and…
You may also like this about ROMAN CONCRETE and that is uses Volcanic ASH + Sea water http://www.google.com.au/search?q=ROMAN+CONCRETE+FORMULA+DISCOVERED+-wiki
Hey I heard that the newer volcanic province near Melbourne include explosive tuff deposits despite being a basaltic province. I wonder why?
Hi Tania,
Well I think “tuff” is just a name for volcanic ash, it doesn’t mean it can’t be from basaltic volcanism. There is quite a bit of evidence in the Newer Volcanic Province for violent eruptions, such as phreatomagmatic and phreatic explosions, which can result in tuff deposits (e.g., Tower Hill, Lake Purrumbete).
Cheers,
Stephanie
YOU REFER TO A( KOALA BEAR )IN YOUR PICTURES THERE IS NO SUCH ANIMAL WE DO NOT HAVE BEARS IN AUSTRALIA THE ANIMAL IS A KOALA
Hi John,
Yes, you are right! This first thing the comes up in Google when I looked up “koala bear” is “…Koalas aren’t bears as many people are led to believe…” haha! I will fix this mistake asap. Please forgiven me, I am not Australia after all, but should know better by now having lived here for almost 2 years!
Stephanie
sorry I did not realize you were not of aussie stock I thought you were from he state of tas my apologies for being so stern
John Mangan
No worries 😉
Hi Stephanie,
You mentioned a reference ‘Airey’s Inlet (Cas et al., 1994)’.
I was wondering if you could provide the full reference for this.
Cheers,
Joel
Hi Joel
I have a couple of papers on the volcanics at Aireys Inlet (Reeckmann 1994 and McLaren et al. 2009). If you drop me an email at Julie.Boyce@monash.edu I’ll pass them on.
Julie
Hey Joel, the full reference is:
Cas, R., Simpson, C., and Sato, H., 1993, Newer Volcanics Province – Processes and products of phreatomagmatic activity, IAVCEI Canberra 1993 General Assembly, Post-conference field trip C-5, Excursion guide, 95 p.
Your question actually highlighted a mistake I made in the post, it should be 1993 not 1994. I will fix this right away. If you send me your email I can give you the pdf copy of this field trip manual. Sounds like Julie Boyce has some more papers as well she can pass along to you (thanks Julie)!
Cheers,
Stephanie
hi stephanie–i’d love a pdf copy of the field trip manual if you still have it–i’m going on a road-trip through southern victoria in a couple of months.
Hey Fionnuala,
Awesome, hope you have a great trip! I will just make sure it is ok to distribute the field trip manual, and if so I will send it to you via email (fionnuala.sheehan@gmail.com – correct?).
Cheers,
Stephanie
Hi Stephanie,
Great website. I live in Melbourne and am planning a trip to Western Victoria and would also appreciate a copy of your field trip manual if ok.
Many thanks, Alan
Hi Stephanie, I found your post very interesting. Is it possible for a maar-diatreme to erupt again? If so, will the large volume of water turn into water vapour?
Hey Kris,
The last eruption (and only known eruption in modern times) was in the Ukinrek Maars in 1977 in the Aleutian Range, Alaska. It is very possible for a maar-diatreme to erupt again and there are is lots of evidence for these type of events in the geological record (e.g. diatreme breccia pipes within large copper deposits). I am not an expert on the subject, but it is very tough to predict when and where the next one will erupt. Yes there will be a large volume of water vapour associated with a maar-diatreme volcanic eruption, but it will also be mixed with ash and other volcanic ballistics. I can send you some papers on maar-diatreme volcanoes if you are interested. Cheers!
Stephanie
Great post Stephanie. That red oxidised scoria layer you took a photo of at Mt Rouse is actually a surge, and it’s loaded with Pele’s tears and hairs =)
Hey Julie!
Ah, I should have looked harder to find the tears and hairs! Thanks for letting me know, and I’m glad you liked the post. I read your paper before going to the NVP and really liked the job you did with compiling all the volcanic centres (and having it available on Google Earth). I look forward to reading more from you in the future!
-Stephanie
Hello Stephanie, I really enjoyed your post, and I discovered it by this site: http://all-geo.org/metageologist/2015/02/hot-spot-volcanoes-without-mantle-plumes/
I’m a brazilian geology student, and I would like to know if you have posts about mantle processes, mainly involving alkaline rocks and alkaline volcanics!
Hi Eduardo, thanks I’m glad you enjoyed the post! I don’t have any posts about mantle processes involving alkaline rocks at the moment, but possible in the future I will write about it. If you give me your email I can send you some papers on alkalic rocks. Cheers!
Sure! eduardovalentindossantos@gmail.com
[…] in Victoria, Australia. To get a great overview of its many great volcanic features, check out this post (from which the photos here come). The lava is basaltic in composition – just what […]
Before I present your images of rocks on my blog, 🙂 would you mind say few words on the cute blue “pebbles” seen on the fourth image from top of the post? Another image on the right side, also about peperite, shows small, spots nearly, granules of the same milk-blue color? Sort of a bonanza? 🙂
And thanks for another part of Geo Science in a Nutshell!
Hello! The little blue pebbles-like things are small organisms, little barnacles if I recall correctly. Hope that helps, cheers!
I’m afraid I was misunderstood. I pointed to the picture of yours:
https://exploringthearth.files.wordpress.com/2015/01/aireys-inlet-peperite-21.jpg
Caption – “Possible peperite at Airey’s Inlet. Rounded basalt clasts are within overlying limestone – Victoria, Australia”
Peperite can be scenic but the blue rocks are unique. I haven’t found them in such quantity, if at all, in mountainous rivers.
Look at the stones around your feet.
The barnacles you said found in Wikipedia look different:
https://en.wikipedia.org/wiki/Barnacle
The milk-blue pebbles resemble those found on other pictures from Wikipedia:
1. https://en.wikipedia.org/wiki/Pebble
1.a. https://en.wikipedia.org/wiki/File:Pebbleswithquarzite.jpg
https://upload.wikimedia.org/wikipedia/commons/7/77/Pebbleswithquarzite.jpg
1.b. https://en.wikipedia.org/wiki/File:Beach_pebble.jpg
https://upload.wikimedia.org/wikipedia/en/5/5b/Beach_pebble.jpg
1.c. https://en.wikipedia.org/wiki/File:Pebbles_on_beach_at_Broulee_-NSW_-Australia-2Jan2009.jpg
https://upload.wikimedia.org/wikipedia/commons/9/9e/Pebbles_on_beach_at_Broulee_-NSW_-Australia-2Jan2009.jpg
1.d. https://en.wikipedia.org/wiki/File:Valuga_Beach.png
https://upload.wikimedia.org/wikipedia/commons/f/f5/Valuga_Beach.png
1.e. https://pl.wikipedia.org/wiki/Plik:Pebbles-oliv-e.jpg
https://upload.wikimedia.org/wikipedia/commons/b/b1/Pebbles-oliv-e.jpg
Regards, 🙂
Hi Phoenix,
Sorry for the misunderstanding! I thought you were referring to the other close-up photo of the peperite. Yes in this photo the large blue pebble are quite nice, but I think the blue colour is a bit skewed as I enhanced the photo slightly to bring out the peperite texture. I am also on a beach, not a mountainous river, so round beach rocks are fairly common. While they look nice and blue, in reality they are mostly a dark grey-green basalt. Thanks for your interest though and all the pictures, I hope I helped you clarify the pebbles. Cheers!
Stephanie
I really enjoy your blog posts Stephanie. The World Geothermal Congress is being held in Melbourne, April 19-24. http://wgc2015.com.au/ I’m sure your research will be useful for geothermalists looking for resources in Victoria.
Hi Ian,
Thanks I’m glad you liked it! My current research isn’t actually focused on geothermal activity in Victoria so I thus won’t have much to present. But I do work within an active geothermal system elsewhere for my university studies so perhaps one day I will present some of my work at a geothermal conference. Cheers!
Stephanie