Mud Volcanoes
Mud volcanoes aren’t like typical volcanoes that spew molten lava from the
mantle.
For one thing they are generally cold.
If classic volcanoes vomit the earth’s churning guts, then mud volcanoes
are more like a burp.
There are about 1,100 mud volcanoes that have been identified around the
world, and nearly 400 of them can be found in and around the hydrocarbon
bearing strata of Azerbaijan.
They form when fluids and gases that have built up under pressure inside
the Earth find an escape route to the surface via a network of fractures.
The fluids move up these cracks, carrying mud with them, creating the mud
volcanoe as they escape.
Gryphons are small mud cones up to a few meters high, can be numerous, and
often are aligned with tectonic structures.
The erupted materials are three-phase: solids, water, and gases, the
latter being dominantly methane CH
4 and carbon dioxide CO
2.
Elements likely needed to create a mud volcanoe...
- rapid accumulation of great thicknesses of unconsolidated sediments
- a fairly uniform fine particle size, often shale size
- high water content
- pressurised high methane CH4 carbon dioxide CO2
content
- often an impermeable cap rock or unconsolidated material (like shale
or clay)
- a souce of increasing pressure either by overlying strata, tectonic
movement or heat via volcanism
- a restricted escape route to the surface
Cold Mud Volcanoes
Mud volcanoes are often associated with petroleum deposits and tectonic
subduction zones and orogenic belts; hydrocabon methane gas is erupted.
Reduced pressure causes to be entrapped gases to expand. Lower density
causes the saturated unconsolidated muddy/silty sediment to liquify.
When an escape route for the wet pressurised mud activates, the reduced
pressure on the entrapped methane or carbon dioxide CO
2 causes
it to change from liquid to gaseous state.
To do this heat is extracted from the surrounding mud. This makes the mud
cooler.
Hot Mud Volcanoes
They are also associated with lava volcanoes; in the case tectonic heat
causes the water and entrapped gas usually H
2 or CO
2
to expand. The result is a mud slurry exudate. This material is then
forced upwards by the pressure of its own expansion. through a local
geological fault or fissure.
Overpressure within the Earth builds up when underground fluids are unable
to escape from beneath the weight of overlying sediments. Some of this
fluid was trapped within the sediment when it was deposited. Other fluids
may migrate in from deeper sediments, while still others may be generated
in place by chemical reactions in the sediments. One important type of
chemical reaction generates oil and natural gas. Finally, fluids may
become overpressured if they are squeezed by tectonic forces during
mountain building. Mud volcanoes are also useful to scientists as windows
into conditions deep inside the Earth.
Some current theories on mud volcanoes include...
- bodies of remobilised shale are called shale diapirs and are thought
to be formed by growing upwards from depth due to buoyancy or
- by high sediment accumulation rates and inefficient expulsion of
water or
- because of insuffiant accommodational pore spaces that are
principally due to tectonic compressions or shale diapirsm can also
occur due to differential loading or
- sedimentary basins, pore water can locally become supercritical
which drives the expulsion of gas, liquid, mud and clasts to the
surface where each expulsion of mud to the earth surface is
interpreted as an act of pressure equilibratation between the mud
chamber and surface
The exact mechanisms for the formation of mobile shale mud is still not
well known.
Mud volcanism on other planets (e.g. Mars and Titan), and microbial
activity associated with gas seepage represent emerging issues and
opportunities for future research.
Mud Volcanoes in Australia -Apsley Mud Mounds
The mud springs are a unique geological feature, being possibly one of
only two such formations in Australia.
Location: 2 Hawbridge Street, Carseldine, Queensland 4034.
From 1865, the mud springs were part of a farm. In 1970, Brisbane City
Council works disturbed the site resulting in an eruption of hot mud and
stinking hydrogen sulphide gas H
2S. A concrete cap was placed
over the mud springs to stop the flow and the site fenced for public
safety. In 1979, the site became a park.
This property contains a rare geological formation, hot mud springs, of
which there is possibly only one other similar site in Australia. The mud
springs have a subterranean depth of 30 metres and comprise a dome of
methane gas under a clay cap.
They are connected by an underground stream to a sub artesian basin that
runs as far as Bald Hills. Originally the mud springs had two outlets,
with one at the present location of this park and the other being further
east near what is the section of Gympie Road that is north of Cabbage Tree
Creek.
The area containing these two mud springs would have been known to the
Undanbi people and may have had some spiritual significance for them.
Because of its unique geological activity, the mud mounds site was
selected in 1970 for a test bore to be drilled in the search for natural
gas.
The bore was sunk to a depth of 360 metres and testing gave indications
that there were substantial reserves of methane gas underground to a depth
of 1,300 metres.
Also in 1970, the Brisbane City Council began laying a large water main
across Graham Road, to service the planned residential redevelopment of
farmland in the area.
In the process, the Council demolished the mud mounds and this led to a
large amount of hot mud pouring out of the resultant hole in the ground.
It moved in two streams “like a giant toothpaste tube” across Hawbridge
Street thereby blocking access.
As well, hydrogen sulphide gas began to escape into the atmosphere causing
a terrible stench to permeate the surrounding area. Hawbridge Street had
to be closed for eight weeks, as Council trucks removed the mud from the
site, causing the ground to sink.
In the end, the Council resorted to dumping sheet pilings onto the mud to
form a caisson for its water pipes plus twelve truckloads of cement were
poured over the pipes to secure them in place.
At the completion of this work, the earth crust covering the mud springs
was only 15 centimetres thick. So, as a safety precaution, the mud springs
site was enclosed by a high fence, with warning signs erected, advising
the public to keep off the area
Sources
https://www.sciencedirect.com/science/article/abs/pii/S0012825216302197
https://theconversation.com/what-are-mud-volcanoes-173198
https://www.smithsonianmag.com/smart-news/azerbaijan-mud-volcano-erupts-fiery-fashion-180978120/
https://www.accuweather.com/en/weather-news/mud-volcano-produces-explosion-near-azerbaijan-in-caspian-sea/975009
https://stopandstay-7wonders.blogspot.com/2011/04/mud-volcano.html
https://www.fluid-venting-system.org/mud-volcano-taiwan-island.html
https://link.springer.com/chapter/10.1007/978-3-030-64308-9_12
https://www.searchanddiscovery.com/pdfz/documents/2017/70261gulmammadov/ndx_gulmammadov.pdf.html
Mud Volcano cross-section image from... Mazzini A, Etiope G (2017) Mud
volcanism: an updated review. Earth Sci Rev 168:81–112
https://www.researchgate.net/profile/Sverre-Planke/publication/226567150/figure/fig1/AS:302241463455745@1449071388253/The-distributions-of-active-mud-volcanoes-in-Azerbaijan-Az-The-numbered-mud.png
brisbane-mud-springs-park_480.pdf