18. May 2020
'Making a mess' in the name of research

La­va-like mud flows on Mars

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Space
A mud volcano on Mars?
A mud vol­cano on Mars?
Image 1/4, Credit: NASA/JPL-Caltech/University of Arizona

A mud volcano on Mars?

Mud vol­can­ism is sus­pect­ed to have oc­curred in many places on Mars but its ex­is­tence can­not be iden­ti­fied be­yond doubt with cur­rent­ly avail­able da­ta. This im­age shows a crater cone built up of fine lay­ers. The frac­ture pat­terns around the crater may in­di­cate dried mud. Nev­er­the­less, it can­not be ruled out that this crater is the re­sult of ‘con­ven­tion­al’ vol­can­ism.
Active mud volcanoes on Earth
Ac­tive mud vol­ca­noes on Earth
Image 2/4, Credit: CAS/Peter Brosž CC BY-SA 4.0

Active mud volcanoes on Earth

Mud vol­ca­noes are not as well-known as ‘clas­sic’ vol­ca­noes, which bring la­va – that is, molten rock – from Earth's in­te­ri­or to the sur­face, but they are com­mon all over the world. Ge­ol­o­gists have dis­cov­ered ap­prox­i­mate­ly 1800 mud vol­ca­noes on Earth, some of them at the bot­tom of the sea. Al­most half of these mud vol­ca­noes are lo­cat­ed in Azer­bai­jan, near the Caspi­an Sea coast. There, the erup­tion pro­cess and the flow dy­nam­ics of the es­cap­ing mud flows can be stud­ied in-situ. The small mud vol­cano in the im­age is on­ly a few me­tres high, while oth­ers are sev­er­al kilo­me­tres in di­am­e­ter.
Mud volcanoes on Mars?
Mud vol­ca­noes on Mars?
Image 3/4, Credit: ESA/DLR/FU Berlin CC BY-SA 3.0 IGO

Mud volcanoes on Mars?

For years there have been dis­cus­sions about whether some vol­ca­noes on Mars are not mag­ma-fed, but mud vol­ca­noes. On Earth, there are ap­prox­i­mate­ly 1800 of these vol­ca­noes. Dozens of com­par­a­tive­ly small hills with cen­tral craters have been dis­cov­ered in the Mar­tian re­gion of Chryse Plani­tia, in­to which nu­mer­ous wide, now dry chan­nels ter­mi­nate. These are dis­tribut­ed in this low­land plain (left of cen­tre in this con­trast-en­hanced Mars Ex­press HRSC false-colour im­age). The flat, al­most pan­cake- or cow­pat-like, bright ar­eas on the right of the im­age may al­so have been formed by mud flows. Lab­o­ra­to­ry ex­per­i­ments, in which DLR Mars ge­ol­o­gist Ernst Hauber was in­volved, sup­port the the­o­ry that mud vol­can­ism is al­so pos­si­ble in the cold con­di­tions found on Mars, with its thin at­mo­sphere. How­ev­er, the flow be­haviour is com­plete­ly dif­fer­ent from that on Earth due to the much low­er at­mo­spher­ic pres­sure and tem­per­a­tures.
Conditions on Mars simulated in a low-pressure chamber
Con­di­tions on Mars sim­u­lat­ed in a low-pres­sure cham­ber
Image 4/4, Credit: CAS/Peter Brosž CC BY-SA 4.0

Conditions on Mars simulated in a low-pressure chamber

The at­mo­spher­ic pres­sure on Mars is ap­prox­i­mate­ly 150 times low­er that that found at sea lev­el on Earth, and tem­per­a­tures are much low­er most of the time and in most re­gions. In the sub­po­lar low­lands, they of­ten drop to mi­nus 100 de­grees Cel­sius at night. Un­der these pres­sure and tem­per­a­ture con­di­tions, how does wa­ter-sat­u­rat­ed mud flow over the sur­face of Mars? A group of Eu­ro­pean sci­en­tists has at­tempt­ed to close this knowl­edge gap and poured wa­ter-rich mud on­to a cold sand sur­face in a low-pres­sure cham­ber (in the im­age – one of the sci­en­tists in­volved in the study, Ondřej Krýza from the Czech Acade­my of Sci­ences) at the Open Uni­ver­si­ty in Mil­ton Keynes (UK) and ob­served the flow be­haviour (see video). In par­tic­u­lar, the low at­mo­spher­ic pres­sure on Mars changes the flow be­haviour dras­ti­cal­ly com­pared to what oc­curs on Earth – it re­sem­bles thin, low-vis­cous basaltic la­va.
  • Laboratory experiments show that at very low temperatures and under very low atmospheric pressure, mud behaves similar to flowing lava on Earth.
  • Results suggest that tens of thousands of conical hills on Mars, often with a small crater at their summit, could be the result of mud volcanism.
  • Focus: Space, exploration

Scientists have long suspected that the 'fire-breathing' volcanoes that spread large quantities of flowing lava over Mars were not the only kind. The numerous mountain cones in the northern hemisphere of the Red Planet may be the result of mud volcanoes. However, until now, researchers have lacked knowledge about the behaviour of water-rich mud on the surface of Mars. An unusual laboratory experiment involving the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has now been able to show how mud flows at very low temperatures and under reduced atmospheric pressure. It behaves in a similar way to very specific lava flows on Earth. The results, which have now been published in the journal Nature Geoscience, add important details to the existing knowledge of Mars and its history, which has been shaped by volcanic activity.

"We have long been aware that in the early history of Mars, several billion years ago, large amounts of water were released over a short period of time, eroding very large valleys in the landscape, which have long since dried up," explains Ernst Hauber of the DLR Institute of Planetary Research in Berlin-Adlershof, who was involved in the study. "Extensively eroded masses of fragmented rock were transported through these outflow channels and into the northern lowlands of the planet, where they were quickly deposited. Later, these rocky masses were covered by younger sediments and volcanic rocks." Some Mars researchers had previously suspected that these underground, water-rich sediments could have become liquefied under certain circumstances and been pushed back up to the surface under pressure. In reference to the similar rise of magma, this process, which is well documented in many sedimentary basins on Earth, is referred to as sedimentary volcanism or mud volcanism.

Are small volcanic cones the result of mud extrusions?

Tens of thousands of conical hills populate the northern highlands of Mars, often with a small crater at their summit. These may be the result of mud volcanism. However, the evidence for this is not easy to acquire. This is due to the fact that little is known about the behaviour of low-viscosity mud under the environmental conditions on the Martian surface. To fill this knowledge gap, a group of European scientists carried out a series of experiments in a cylindrical low-pressure vessel 90 centimetres in diameter and 1.8 metres long, in which water-rich mud was poured over a cold sandy surface. Apart from the gravity on Mars, which could not be simulated, this experimental setup was somewhat reminiscent of building a large sandcastle under Mars-like conditions.

How does wa­tery-mud move on Mars? Like pa­hoe­hoe la­va!
Ex­plo­ration of Mars has re­vealed the pres­ence of large out­flow chan­nels which have been in­ter­pret­ed as the prod­ucts of catas­troph­ic flood events dur­ing which a large quan­ti­ty of wa­ter was re­leased from the sub­sur­face. The rapid buri­al of wa­ter-rich sed­i­ments fol­low­ing such flood­ing may have pro­mot­ed an ide­al set­ting to trig­ger sed­i­men­ta­ry vol­can­ism, in which mix­tures of rock frag­ments and wa­ter erupt to the sur­face in the form of mud.
Credit: Geofyzikální ústav AV ČR v. v. i.

The aim of these unusual experiments was to find out how the changed physical parameters influence the water component of the mud and thus alter its flow behaviour. The results came as a surprise. "Under the low atmospheric pressure of Mars, the mud flows behave in much the same way as 'pāhoehoe', or 'ropy', lava, which is familiar from large volcanoes on Hawaii and Iceland," says the lead author of the study, Petr Brož of the Czech Academy of Sciences. These findings were somewhat unexpected, as comparable geological processes on other bodies in the Solar System are thought to occur in a similar way to conventional volcanic processes on Earth. "Our experiments show that even a process as apparently simple as the flow of mud – something that many of us have experienced for ourselves since we were children – would be very different on Mars."

Did water-rich sediments also reach the Martian surface?
Did water-rich sediments also reach the Martian surface?
Water that flowed over the surface of Mars billions of years ago transported large quantities of sediments to the northern lowlands, where they were later covered by younger sediments and volcanic rocks. Some Mars researchers suspect that these water-rich sediments became liquefied underground and rose back to the surface under pressure – similar to this hot ‘mud spring’ at Bakhar in Azerbaijan (diameter approximately 1.5 metres). Experiments in a low-pressure chamber, in which DLR scientist Ernst Hauber was involved, have now shown that the flow behaviour is similar to that of what is referred to as ‘ropy lava’ (or, according to the Hawaiian term for smooth, unbroken lava, also known as ‘ pāhoehoe’ lava), which is at a temperature of several hundred degrees Celsius. This implies that mud flows on Mars take a completely different course than those on Earth. This observation could support the assumption that many of the conical hills with central craters discovered in the north of Mars are also mud volcanoes.
Credit: CAS/Peter Brosž CC BY-SA 4.0

Major impact of low atmospheric pressure

The key reason for the flow behaviour of the mud is the very thin atmosphere of Mars. The pressure is 150 times lower than the pressure at sea level on Earth. This difference has a major impact. Under such conditions, liquid water on the Martian surface is not stable and begins to boil and evaporate. This process absorbs latent heat in the vapor and cools the remaining mud, which then freezes at its surface, forming a crust. In a phase transition, such as during a freezing or thawing process, latent heat is released or absorbed by a material without changing its temperature. “Of course, we already know that liquid water begins to boil sooner under low pressure – that is why, for example, it takes longer to cook pasta on a camping stove on high mountains on Earth," explains Hauber. "However, the impact of this familiar effect on mud has never been investigated in an experiment before. Once again, it turns out that different physical conditions must always be taken into account when looking at apparently simple surface features on other planets. We now know that we need to consider both mud and lava when analysing certain flow phenomena," adds Hauber.

The team of researchers were able to show in detail that the mud flows in the experiment behaved like pāhoehoe lava, with liquid mud spilling from ruptures in the frozen crust, and then refreezing to form a new flow lobe. When mud escapes onto the Martian surface, it is able to flow for some time before it solidifies due to the low temperatures. However, the morphology – the shape of the mud flows – is different from those found on Earth. The research work that is currently being carried out is important for investigations of other planetary bodies, because similar processes may also play a role in cryovolcanic eruptions, in which liquid water comes to the surface, instead of magma or mud, such as on icy moons in the outer Solar System.

Contact
  • Falk Dambowsky
    Ed­i­tor
    Ger­man Aerospace Cen­ter (DLR)
    Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
    Contact
  • Ernst Hauber
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-325
    Fax: +49 30 67055-402
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • Mgr. Petr Brož
    Czech Acade­my of Sci­ences
    In­sti­tute of Geo­physics
    Telephone: +420 267 103-063
    Boční II 1401
    141 31 Prag
    Contact
  • Ulrich Köhler
    Pub­lic re­la­tions co­or­di­na­tor
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-215
    Fax: +49 30 67055-402
    Rutherfordstraße 2
    12489 Berlin
    Contact

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