Carbonatites are strange igneous rocks made up mostly of

carbonates – common minerals like calcite, calcium carbonate. Igneous rocks

that solidify from molten magma usually are high-temperature rocks containing

lots of silicon which results in lots of quartz, feldspars, micas, and

ferro-magnesian minerals in rocks like granite and basalt. Carbonatites

crystallize from essentially molten calcite, and that’s really unusual.

Most carbonatites are intrusive, meaning they solidified

within the earth, and it wasn’t until 1960 that the first carbonatite volcano

erupted in historic times, proving that they form from cooling magma. The

eruption at Ol Doinyo Lengai in Tanzania occurred on a branch of the East

African Rift System, and most carbonatites are associated with these breaks in

continental crust where eventually a new ocean may form.

Mt Lengai, Tanzania, photo by Clem23

(Creative Commons License - source)

Eruptions at Lengai, whose name means “mountain of god” in

the Maasai language, are the lowest-temperature magmas known because calcite

melts at a much lower temperature than silica-rich compounds, around 510

degrees C versus 1000 degrees or more for most magmas. It isn’t even red-hot

like most lava flows.

A simple and early interpretation of carbonatites was that

they represented melting of limestone, but geochemical data indicate that they

really do come from primary igneous material that probably originated in the

mantle. Exactly how they form is debated, in part because they are so rare, but

one idea is that they result from special cases of differentiation within more

common magmas, or maybe an example of certain chemicals – the carbonates – separating

out in an unusual way.

Another unusual aspect of carbonatites is the minerals

associated with the dominant calcite. It’s common to get rare-earth compounds,

tantalum, thorium, titanium, and many other minerals that are unusual in high

concentrations in other settings. The Mountain Pass rare-earth deposit in

California, once the largest producer of rare earths in the world, is in a

Precambrian carbonatite. Rare earths are used in lots of modern technologies,

including turbines for wind energy, batteries in electric car motors, cell

phones, solar cells, and eyeglasses.

Rare earths are also produced from the Mt. Weld carbonatite

in Western Australia, but it’s more famous for its tantalum, an element that’s

vital in capacitors for cell phones, video games, and computers. Australia has

by far the greatest reserves of tantalum, but mining didn’t begin until 2011

and production is just now ramping up. The United States, which is 100%

dependent on imports for tantalum, imports most of it from Brazil, Rwanda,

China, and Kazakhstan.

Magnetite is a common associated mineral in carbonatites,

and at Magnet Cove, Arkansas, there’s enough to give the name to the place. It’s

also rich in titanium, often in the form of the mineral rutile, titanium dioxide.

When I was there on a geology field trip in 1969, I remember walking into the

Kimzey Calcite Quarry. It was like walking into a giant calcite crystal, with

gigantic cleavage faces the size of a person or bigger. We collected lots of cool

rutile and pyrite crystals.

More common economic minerals can be associated with

carbonatites as well. At one in South Africa the main products are copper and

vermiculite.

While I said earlier that carbonatites are really rare,

there are still a few dozen known. It’s possible that their rarity is a

reflection of the fact that calcite is much more easily eroded and dissolved

than the typical basaltic rocks that derive from most volcanoes, so they may

simply be poorly preserved.

—Richard I. Gibson

As near as I can tell in the original daily series in 2014,

I never addressed the topic of turbidity currents and their sedimentary

product, turbidites. But they account for the distribution of vast quantities

of sediment on continental shelves and slopes and elsewhere.

You know what turbid water is: water with a lot of suspended

sediment, usually fine mud particles. In natural submarine environments,

unconsolidated sediment contains a lot of water, and when a slurry-like package

of sediment liquifies, it can flow down slopes under gravity, sometimes for

hundreds of kilometers.

It isn’t correct to think of these streams of water and

sediment as like rivers on the sea floor. Rivers transport sediment, whether

boulders or sand or silt or mud, through the traction, the friction of the

moving water. Turbidity flows are density flows, moving because the density of

the water-sediment package is greater than the surrounding water. That means

they can carry larger particles than usual.

Turbidite formation. Image by Oggmus, used under Creative Commons license - source

Sometimes a turbidity flow is triggered by something like an

earthquake, but they can also start simply because the material reaches a

threshold above which gravity takes over and the material flows down slope. The

amount and size of sediment the flow can carry depends on its speed, so as the

flow diminishes and wanes, first the coarse, heavier particles settle out,

followed by finer and finer sediments. This results in a sediment package

characterized by graded bedding – the grain size grades from coarse, with

grains measuring several centimeters or more, to sand, 2 millimeters and

smaller, to silt and finally to mud in the upper part of the package. Repeated

turbidity flows create repeated sequences of graded bedding, and they can add

up to many thousands of meters of total sedimentary rock, called turbidites.

Other sedimentary structures in turbidites can include

ripple marks, the result of the flow over an earlier sediment surface, as well

as sole marks, which are essentially gouges in the older finer-grained top of a

turbidite package by the newest, coarser grains and pebbles moving across it.

There are variations, of course, but the standard package of

sediment sizes and structures, dominated by the graded bedding, is called a

Bauma Sequence for Arnold Bouma, the sedimentologist who described them in the

1960s.

Turbidity currents are pretty common on the edges of

continental shelves where the sea floor begins to steepen into the continental

slope, and repeated turbidity flows can carve steep canyons in the shelf and

slope. Where the flow bursts out onto the flatter abyssal sea floor, huge

volumes of sediment can accumulate, especially beyond the mouths of the great

rivers of the world which carry lots of sediment.

When the flow is no longer constrained by a canyon or even a

more gentle flow surface, the slurry tends to fan out – and the deposits are

called deep abyssal ocean fans. They are often even shaped like a wide fan,

with various branching channels distributing the sediment around the arms of

the fan. The largest on earth today is the Bengal Fan, offshore from the mouths

of the Ganges and Brahmaputra Rivers in India and Bangladesh. It’s about 3,000

km long, 1400 km wide, and more than 16 km, more than 10 miles, thick at its

thickest. It’s the consequence of the collision between India and Eurasia and

the uplift and erosion of the Himalaya.

The scientific value of turbidites includes a record of

tectonic uplift, and even seismicity given that often turbidity currents are

triggered by earthquakes. They also have economic value. Within the sequence of

fining-upward sediments, some portions are typically very well-sorted, clean

sandstones. That means they have grains of uniform size and shape and not much

other stuff to gum up the pores between the sand grains – so that makes them

potentially very good reservoirs for oil and natural gas. You need the proper

arrangements of source rocks, trapping mechanisms, and burial history too, but

deep-water turbidites are explored for specifically, and with success, in the

Gulf of Mexico, North Sea, offshore Brazil and West Africa, and elsewhere. The

Marlim fields offshore Brazil contained more than 4 billion barrels of

producible oil reserves when they were discovered in the 1980s.

Ancient

turbidites sometimes serve as the host rocks for major gold deposits, such as

those at Bendigo and Ballarat Australia, which are among the top ten gold

producers on earth.

—Richard I. Gibson

This episode is about some of the interesting

connections that arise in science.

We’ll start with me and my first professional job as a

mineralogist analyzing kidney stones. My mineralogy professor at Indiana

University, Carl Beck, died unexpectedly, and his wife asked me as his only

grad student to carry on his business performing analysis of kidney stones. Beck

had pioneered the idea of crystallographic examination to determine mineralogy

of these compounds because traditional chemical analysis was misleading. For example,

some common kidney stones are chemically calcium phosphates and calcium

carbonates – but they are hardly ever calcium carbonate minerals. That makes a

big difference in terms of treatment, because calcium carbonate minerals can be

dissolved with acids, while calcium phosphate cannot. The carbonate is actually

part of the phosphate mineral structure, partially substituting for some of the

phosphate. Other subtleties of mineral crystallography can distinguish between different

minerals and can point to specific kinds of treatments, more than just

chemistry can.

One of the most common minerals in kidney stones is called

whewellite – calcium oxalate, CaC2O4 with a water molecule as part of its structure.

In kidney stones it usually forms little rounded blobs, but sometimes the way

the mineral grows, it makes pointy little things called jackstones, for their

similarity to children’s’ jacks. And yes, those can be awfully painful, or so I’m

told.  Whewellite is really rare in the

natural world beyond the urinary system, but it does exist, especially in

organic deposits like coal beds. Whewellite was named for William Whewell,

spelled Whewell, a true polymath and philosopher at Cambridge University in

England during the first half of the 19th century. He won the Royal

Medal for his work on ocean tides and published studies on astronomy,

economics, physics, and geology, and was a professor of mineralogy as well.

Mary Somerville, 1834 painting by
Thomas Phillips - source

Whewell coined many new words, particularly the word “scientist.”

Previously such workers had been called “men of science” or “natural

philosophers” – but Whewell invented the new word scientist for a woman, Mary

Somerville. Somerville researched in diverse disciplines, especially astronomy,

and in 1835 she became one of the first two female members of the Royal

Astronomical Society, together with Caroline Herschel, discoverer of many

comets and nebulae.

In 1834 Somerville published “On the Connexion of the

Physical Sciences,” a synthesis reporting the latest scientific advances in

astronomy, physics, chemistry, botany, and geology. William Whewell wrote a

review in which he coined the word scientist for Somerville, not simply to

invent a gender-neutral term analogous to “artist,” but specifically to recognize

the interdisciplinary nature of her work. And even more, according to Somerville’s

biographer Kathryn Neeley, Whewell wanted a word that actively celebrated “the

peculiar illumination of the female mind: the ability to synthesize separate

fields into a single discipline.” That was what he meant by a scientist.

Somerville was born in Scotland in 1780 and died in 1872 at

age 91. Her legacy ranges from a college, an island, and a lunar crater named

for her to her appearance on Scottish bank notes beginning in 2017. Besides the

mineral whewellite, William Whewell is also memorialized in a lunar crater and

buildings on the Cambridge campus, as well as in the word scientist, included

in the Oxford English Dictionary in 1834, the same year he coined it. He died

in 1866.

—Richard I. Gibson

LINK:

Article about Whewell and Somerville 

Today we’re going back about 280 million

years, to what is now Uruguay in South America.

280 million years ago puts us in the early part of the

Permian Period. Gondwana, the huge southern continent, was in the process of

colliding with North America and Eurasia to form the supercontinent of Pangaea.

South America, Africa, Antarctica, India, and Australia had all been attached

to each other in Gondwana for several hundred million years, and the extensive

glaciers that occupied parts of all those continents were probably still

present in at least in highlands in southern South America and South Africa, as

well as Antarctica.

But the area that is now in Uruguay was probably in cool,

temperate latitudes, something like New Zealand or Seattle today. The

connection between southern South America and South Africa was a lowland,

partially covered by a shallow arm of the sea or perhaps a broad, brackish

lagoon at the estuary of a major river system that was likely fed in part by

glacial meltwater from adjacent mountains. We know the water was shallow

because the rocks preserve ripple marks produced by wave action or currents.

The basin must have been near the shore because delicate

fossils such as insect wings and plants are among the remnants. It looks like

this shallow sea or lagoon became cut off from the ocean, allowing the waters

to become both more salty, even hypersaline, and anoxic, as the separation

restricted inflows of water, either fresh or marine, that could have continued

to oxygenate the basin. In the absence of oxygen, excellent preservation of

materials that fell to the basin floor began, and there were few or no

scavenging animals to disrupt the bodies.

The rocks of the Mangrullo Formation, as it’s called today,

include limestones and siltstones, but the most important for fossil

preservation are probably the extremely fine-grained claystones and oil shales.

These rocks contain some of the best preserved fossil mesosaurs known anywhere.

That’s mesosaurs, not the perhaps more well-known mosasaurs, which are large

whale-like marine reptiles that lived during Cretaceous time. Here, we’re in

the Permian, well before the first dinosaurs.

Mesosaur by Nobu Tamura (Creative Commons license & source) 

Mesosaurs were aquatic reptiles, and they are the earliest

known. They evolved from land reptiles and were among the first to return to

the water to adopt an aquatic or amphibious lifestyle. They were once thought

to be part of a sister group to reptiles, a separate branch of amniotes, which

are animals that lay their eggs on land or bear them inside the mother, like

most mammals do. In that scheme, mesosaurs and reptiles would have diverged

from a common, earlier ancestor. But more recent studies categorize them as

reptiles that split off from the main genetic stem early in the history of the

class, so they’re pretty distant cousins to dinosaurs and all modern reptiles,

but they’re still reptiles. There is ongoing debate among evolutionary

paleontologists as to exactly where mesosaurs fit.

The fossils in Uruguay are so well preserved that we can

identify the gut materials of mesosaurs, and we know they mostly ate

crustaceans, aquatic invertebrates related to crabs, shrimp, and lobsters. The

preservation is so exceptional that in some cases, soft body parts are

preserved including major nerves and blood vessels in mesosaurs and stomachs

and external appendages in the crustaceans. The earliest known amniote embryos

also come from these fossil beds.

Mesosaurs had a short run in terms of their geologic

history, only about 30 million years. They were extinct about 270 million years

ago, well before the great extinction event at the end of the Permian, 250

million years ago. But the presence of coastal-dwelling mesosaurs in both South

America and Africa was a contributing idea in the early development of the

theory of continental drift, since it was presumed that they could not have

crossed the Atlantic Ocean as it is today.

—Richard I. Gibson

Links:

Piñeiro et al. 2012 Environmental conditions 

Paleogeography from Ron Blakey 

Today we’re going to the Mountains of the

Moon – but not those on the moon itself. We’re going to central Africa.

There isn’t really a mountain range specifically named the

Mountains of the Moon. The ancients, from Egyptians to Greeks, imagined or

heard rumor of a mountain range in east-central Africa that was the source of

the river Nile. In the 18th and 19th centuries,

explorations of the upper Nile found the sources of the Blue Nile, White Nile,

and Victoria Nile and identified the Mountains of the Moon with peaks in

Ethiopia as well as 1500 kilometers away in what is now Uganda. Today, the

range most closely identified with the Mountains of the Moon is the Rwenzori

Mountains at the common corner of Uganda, the Democratic Republic of Congo, and

Rwanda.

This location is within the western branch of the East

African Rift system, an 8,000-kilometer-long break in the earth’s crust that’s

in the slow process of tearing a long strip of eastern Africa away from the

main continent. We talked about it in the episode for December 16, 2014.

The long linear rifts in east Africa are grabens, narrow

down-faulted troughs that result from the pulling apart and breaking of the

continental crust. The rifts are famously filled in places by long, linear rift

lakes including Tanganyika, Malawi, Turkana, and many smaller lakes.

Virunga Mountains (2007 false-color Landsat image, annotated by Per Andersson : Source)

When rifting breaks the continental crust, pressure can be

released at depth so that the hot material there can melt and rise to the

surface as volcanoes. In the Rwenzori, that’s exactly what has happened. The Virunga

volcanoes, a bit redundant since the name Virunga comes from a word meaning

volcanoes, dominate the Rwenzori, with at least eight peaks over 10,000 feet

high, and two that approach or exceed 4,500 meters, 15,000 feet above sea

level. They rise dramatically above the floors of the adjacent valleys and

lakes which lie about 1400 meters above sea level.

These are active volcanoes, although several would be

classified as dormant, since their last dated eruptions were on the order of 100,000

to a half-million years ago. But two, Nyiragongo and Nyamuragira, have erupted

as recently as 2002, when lava from Nyiragongo covered part of the airport

runway at the town of Goma, and in 2011 with continuing lava lake activity.

Nyiragongo has erupted at least 34 times since 1882. The volcanic rocks of

these and the older volcanoes fill the rift enough that the flow of rivers and

positions of lakes have changed over geologic time.

Lake Kivu, the rift lake just south of the volcanoes, once

drained north to Lake Edward and ultimately to the Nile River, but the

volcanism blocked the outlet and now Lake Kivu drains southward into Lake

Tanganyika. Local legends, recounted by Dorothy Vitaliano in her book on

Geomythology, Legends of the Earth (Indiana University Press, 1973), tell the

story of demigods who lived in the various Virunga volcanoes. As demigods do,

these guys had frequent arguments and battles, which are probably the folklore

equivalent of actual volcanic eruptions. The stories accurately reflect –

whether through observation or happenstance – the east to west migration of

volcanic activity in the range.

The gases associated with the volcanic activity seep into

the waters of Lake Kivu, which has high concentrations of dissolved carbon

dioxide and methane. Generally the gases are contained in the deeper water

under pressure – Lake Kivu is the world’s 18th deepest lake, at 475

meters, more than 1,500 feet. But sometimes lakes experience overturns, with

the deeper waters flipping to the surface. When gases are dissolved in the

water and the pressure reduces, they can abruptly come out of solution like

opening a carbonated beverage bottle. This happened catastrophically at Lake

Nyos in Cameroon in 1986, asphyxiating 1700 people and thousands of cattle and

other livestock. The possibility that Lake Kivu could do the same thing is a

real threat to about two million people.

The critically endangered mountain gorilla lives in the

Virunga Mountains, which also holds the research institute founded by Dian

Fossey.

—Richard I. Gibson

Today’s episode focuses on one of those

wonderful jargon words geologists love to use: Ophiolites.

It’s not a contrived term like cactolith nor some really

obscure mineral like pararammelsbergite. Ophiolites are actually really important

to our understanding of the concept of plate tectonics and how the earth works

dynamically.

The word goes back to 1813 in the Alps, where Alexandre

Brongniart coined the word for some scaly, greenish rocks. Ophiolite is a

combination of the Greek words for snake and stone, and Brongniart was also a

specialist in reptiles. So he named these rocks for their resemblance to snake

skins.

Fast forward about 150 years, to the 1960s. Geophysical data,

deep-sea sampling, and other work was leading to the understanding that the

earth’s crust is fundamentally different beneath the continents and beneath the

oceans—and we found that the rocks in the oceanic crust are remarkably similar

to the greenish, iron- and magnesium-rich rocks that had been labeled

ophiolites long ago and largely ignored except by specialists ever since.

Those rocks that form the oceanic crust include serpentine

minerals, which are soft, often fibrous iron-magnesium silicates whose name is yet

another reference to their snake-like appearance.  Pillow basalts, iron-rich lava flows that

solidify under water with bulbous, pillow-like shapes, are also typical of

oceanic crust. The term ophiolite was rejuvenated to apply to a specific

sequence of rocks that forms at mid-ocean ridges, resulting in sea-floor spreading

and the movement of plates around the earth.

The sequence usually but not always includes some of the

most mantle-like minerals, such as olivine, another iron-magnesium silicate,

that may settle out in a magma chamber beneath a mid-ocean ridge. Shallower, relatively

narrow feeders called dikes toward the top of the magma chamber fed lava flows

on the surface – but still underwater, usually – that’s where those pillow lavas

solidified.

There are certainly variations, and interactions with water

as well as sediment on top of the oceanic crust can complicate things, but on

the whole that’s the package. So why not just call it oceanic crust and forget

the jargon word ophiolite? Well, we’ve kind of done that, or at least

restricted the word to a special case.

Pillow Lava off Hawaii. Source: NOAA. 

The word ophiolite today is usually used to refer to slices

or layers of oceanic crust that are on land, on top of continental crust. But

wait, you say, you keep saying subduction is driven by oceanic crust, which is

denser, diving down beneath continental crust, which is less dense. Well, yes –

but I hope I didn’t say always.

Sometimes the circumstances allow for some of the oceanic

crust to be pushed up over bits of continental crust, despite their greater

density. One area where this seems to happen with some regularity is a setting

called back-arc basins, which are areas of extension, pulling-apart, behind the

collision zone where oceanic crust and continental crust come together with the

oceanic plate mostly subducting, going down under the continental plate. It

took some time in the evolution of our understanding of plate tectonics for the

idea to come out that you can have significant pulling apart in zones that are

fundamentally compression, collision, but they’re recognized in many places

today, as well as in the geologic past.

It seems to me that back-arc basins are more likely to

develop where the interaction is between plates or sub-plates that are

relatively weak, or small, and more susceptible to breaking. An example is

where two oceanic plates are interacting, with perhaps only an island arc

between them. The “battle” is a closer contest than between a big, strong continent

and weaker, warmer, softer, oceanic crust, so slices of one plate of oceanic

crust may be squeezed up and onto the rocks making up the island arc. This

happens in the southwest Pacific, where the oceanic Pacific Plate and the

oceanic part of the Australian Plate are interacting, creating back-arc basins

around Tonga and Fiji and elsewhere.

It also happens where continental material is narrower, or

thinner, or where the interaction is oblique or complex. One example of this today

is the back-arc basin in the Andaman Sea south of Burma, Myanmar, where the

Indian Ocean plate is in contact with a narrow prong of continent, Indochina

and Malaya.

We’ve now recognized quite a few ophiolites on land,

emplaced there long ago geologically. At Gros Morne National Park in

Newfoundland, the Bay of Islands ophiolite is of Cambrian to Ordovician age.

The area is a UNESCO World Heritage Site for the excellent exposures of oceanic

crust there, not to mention fine scenery.

On Cyprus, the Troodos Ophiolite represents breaking within

the Tethys Oceanic plate as it was squeezed between Gondwana, or Africa, and

the Anatolian block of Eurasia, which is today’s Turkey. The Troodos Ophiolite

is rich in copper sulfides that were probably deposited from vents on a

mid-ocean ridge. In fact, the name Cyprus is the origin of our word copper, by

way of Latin cuprum and earlier cyprium.  

On the island of New Caledonia, east of Australia and in the

midst of the messy interactions among tectonic plates large and small, the

ophiolite is rich in another metal typical of deep-crust or mantle sources:

nickel. There’s enough to make tiny New Caledonia tied with Canada for third

place as the world’s largest producer of nickel, after Indonesia and the

Philippines.

There’s a huge ophiolite in Oman, the Semail Ophiolite,

covering about a hundred thousand square kilometers. It’s one of the most

compete examples anywhere, and it was pushed up on to the corner of the Arabian

continental block during Cretaceous time, around 80 million years ago. Like the

one in Cyprus, this one is also rich in copper as well as chromite, another

deep-crustal or mantle-derived mineral.

The Coast Range Ophiolite in California is Jurassic, about

170 million years old, and formed at roughly the same time as the Sierra Nevada

Batholith developed as a more standard response to subduction. It’s likely that

western North America at that time was somewhat like the southwestern Pacific

today, with strings of island arcs, small irregular continental blocks, and

diverse styles of interaction – the perfect setting for a long band of oceanic

crust to be pushed up and over other material. The whole thing ultimately got

amalgamated with the main North American continent. I talked a bit more about these

events in the episode on the Franciscan, November 7, 2014.

—Richard I. Gibson

LINKS: 

Nice images from Oregon State 

Oman Virtual Field Trip 

In today's episode we’re going to space.

Specifically, Mars. You didn’t really think that earth science is really

limited to the earth, did you? Our topic today will be the Valles Marineris.

The Valles Marineris is a long

series of canyons east of Olympus Mons, the largest mountain in the solar

system. These canyons are about 4,000 km long, 200 km wide and up to 7 km

(23,000 ft) deep. On terrestrial scales, the Valles Marineris is as long as the

distance from New York to Los Angeles. That’s about the same as Beijing to Hong

Kong or Madrid to Copenhagen for our international listeners. They are as wide

as central Florida, central Italy, or the middle of the Korean peninsula. Two

and a half times deeper than Death Valley, though only about 60 percent of the

depth of the Marianas Trench, the lowest point on earth.

Valles Marineris Image Courtesy NASA/JPL-Caltech

Not to be outdone, our planet, Earth,

has even bigger valleys. These occur at the oceanic ridges, where plate

spreading takes place. The longest rift valley on earth lies in the middle of

the Mid-Atlantic Ridge, and it is more than double the length of the Valles

Marineris. But let’s not belittle Mars. After all, while we have a pretty good

idea for how oceanic rifts form on earth, there is quite a bit of debate about

how Mars’ great valley formed.

The most popular theory suggests

that the Valles Marineris are an analog to our oceanic rifts, and formed by the

same process. As the volcanoes of the nearby Tharsis region developed, the

Martian crust bowed down toward the center of the planet due to the weight of

the new volcanic rocks. In time, the crust began to crack. This crack is what we

see in the Valles Marineris. Unlike on Earth, this rift valley did not continue

expanding, but shut down as the Tharsis Region, and Mars as a whole, cooled.

Remember that unlike Earth, Mars does not have plate tectonics. It doesn’t have

a continual process of hot material (like lava) rising to the surface, while relatively cold material (like the oceanic crust) is brought down towards the planet’s center.

More recent work has used

satellite images, and high resolution elevation data to develop new insight

into how the Valles Marineris formed. While images from the 1970’s Mariner 9

orbiter were quite blurry by today’s standards, new missions in the late 90’s

to early 2000’s have given us a better view of the Martian surface than we have

available for the earth. The Mars Reconnaissance Orbiter can take images where

each pixel is about 0.5 m or 20 inches. That is, the color on each image is an

average of an area of 0.25 square meters, or 2.5 square feet. It can then use

image pairs to estimate the elevation of any point on the Martian surface with

a pixel size of 0.25 m, or about 10 inches.

These new satellite images

include multispectral data, or images that look at different wavelengths of

light. The camera on your phone works in the same way: There are sensors that

pick up, red light, green light, and blue light. Your phone records the

intensity of each color in each part of the image, and then plays it back on

your phone’s screen to create a picture.

Some of the satellites orbiting Mars

take this to the next level. They don’t just take different slices of colored

light, but also longer wavelength, infrared light. If you’ve ever seen an image

from a thermal imaging camera, you know what this is. Parts of you show up as

hotter or colder on the screen. It’s the same with the surface of the earth, or

Mars. Scientists can compare the intensity of different wavelengths of light

from each point on the surface. They can then compare these values, with what

would be expected for different rock types. In other words, we’re able to

roughly determine the types of rocks on the Martian surface without ever

setting a boot, or rover tread, on the red planet.

Data from these images has shown

that the Valles Marineris have layered rock formations both on the sides of the

canyons, and within them. The great valley has seen many landslides over the

last 3.5 Billion years of its existence, as well as new and smaller canyons

carved into it. Scientists now speculate that rather than just forming as a big

crack in the Martian surface, the Valles Marineris have been sculpted by

flowing water, either in its liquid form as rivers, or in its solid form as

glaciers.

An alternative hypothesis

proposes that the Valles Marineris formed as a crack during a massive, planetary

scale landslide. This landslide was about half the size of the US or China. How

do you form a landslide that big? Well, you need a large pile of relatively

weak rock, and high elevations for the landslide to flow from.

A key player here is salt. Salt

is relatively weak as compared to rock, and can deform easier when squeezed. It

can also hold water, which can be driven off by heating. On Earth, weak salt

layers are partly responsible for undersea landslides in the Gulf of Mexico.

The Opportunity rover had found some salt layers during its mission on Mars, so

we know salt is present on the red planet.

Some scientists interpret the

layers on the sides of the Valles Merinaris to be made of salt, and possibly

include pockets of ice. This would imply that those layers are weak, and could

potentially move downhill under the right circumstances.

Heating in the Tharsis region

helped de-water salts under the future landslide, melted ice pockets, and

created high elevations on one side of it. Think of it like putting a can on a

wet metal sheet. If you raise one side of the sheet, the can will slide to the

lower side. Just like that, the salty Martian crust broke, and slid downhill.

A crack in the side of this

landslide allowed massive amounts of underground water to escape. As the water

flowed downhill, it eroded the crack to form a massive canyon. This canyon is

the Valles Marineris. The flood that helped form the Valles Marineris was

probably bigger than any seen on earth. Bigger than the massive glacial outburst

floods that formed the channeled scablands of the northwestern United States.

Dick Gibson discussed outburst flooding in the December 27, 2014 episode. Unlike the Earth, the Martian surface has been relatively quiet since

the Valles Marineris formed 3.5 billion years ago.

—Petr Yakovlev

studios of KBMF-LP 102.5 in beautiful and historic Butte, Montana. KBMF is a

local low-power radio station with twin missions of social justice and

education. Listen live at butteamericaradio.org.

As the name implies, mud volcanoes are eruptions of mud –

not molten rock as in igneous volcanoes.  They’re found all around the world,

amounting to about a thousand in total number known. The one thing they have in

common is hot or at least warm water, so they occur in geothermal areas

especially, but they also are found in the Arctic.

They range in size from tiny, just a few meters across and

high, to big things that can cover several square miles. In Azerbaijan some mud

volcanoes reach 200 meters, 650 feet, in height, and around the world many of

them do have conical, volcano-like shapes. But there are others that are just

low mounds, more like a shield volcano.

A little (15-cm) mud volcano in New Zealand.
Photo by Richard Gibson.

The mud is often enough just a slurry of suspended fine-grained

sediment that mixes with the hot water. And by hot water, we don’t necessarily

mean incredibly hot – mud volcano temperatures as cold as a couple degrees Centigrade

are known, but most are associated with temperatures approaching the boiling

point of water.  In some places, like Yellowstone,

the water is acidic which helps it dissolve rocks down to the tiny fragments in

mud, and in other places it may just be the weathered soil and debris picked up

by the water that makes the mud.

Mud volcanoes can erupt violently, or seep slowly, and

emissions can last from minutes to years. I think it’s fair to think of some of

them as geysers in which the water contains a lot of sediment, while others are

more like thick, viscous muddy warm springs.

Besides water and fine sediment, mud volcanoes often contain

natural gas – most commonly methane, but sometimes carbon dioxide, nitrogen, or

other gases. The pressure of these gases is often the driving force behind

eruptions, and with a hydrocarbon gas like methane present you might think mud

volcanoes would be associated with oil and gas fields, and you’d be right. The

hundreds of mud volcanoes in Azerbaijan and in the adjacent Caspian Sea are in

the midst of the first great oil province to be exploited, and some of the petroleum

deposits there are related to structures in the rocks and sediments caused by

the upward force of the mud, which can bend its confining rocks as it rises,

just as a salt dome can do. And since methane is flammable, often enough there

are flames associated with mud volcanoes. In 2001, near Baku, Azerbaijan,

flames shot 15 meters, near 50 feet, into the air. Gobustan in Azerbaijan is a

World Heritage Site for its abundant rock carvings dating to 5000 to 20,000

years ago or more. The flaming methane eruptions of mud volcanoes in Azerbaijan

have been linked to the development of the Zoroastrian religion, and in fact

the name Azerbaijan derives from words meaning Land of the Eternal or Sacred

Fire.

The most destructive mud volcano eruption in recent years

was on the island of Java, in Indonesia, in May 2006. It erupted in the middle

of a rice paddy, and ultimately killed 20 people, caused nearly 3 billion

dollars in damage, and displaced 60,000 people. The mud it erupted covers about

seven square kilometers, nearly three square miles, and in 2018 it continues to

erupt something like 80,000 cubic meters of mud every day – that’s almost 3

million cubic feet, 32 Olympic swimming pools each day.

What caused the violent and extensive eruption of the Lusi

Mud Volcano, also called the Sidoarjo mud flow, on Java is not clear. It may be

simply part of the ongoing natural tectonic and magmatic processes in the

region, which is dotted with many real volcanoes, the kind that carry molten

rock to the surface as lava, and there’s a fault system that may provide a conduit

for hot water from a volcano about 50 kilometers away. Lusi may be an entirely

natural phenomenon. But there are also interesting possible trigger mechanisms.

One suggests that a large earthquake two days before the mud volcano erupted

changed the plumbing system enough to spur the eruption. That’s reasonable,

since we know that earthquakes can have significant effects on geyser systems.

Old Faithful in Yellowstone changed its eruption period following the strong Hebgen

Lake earthquake in 1959. The other possible trigger is nearby drilling by a gas

exploration company, which may have encountered an open pocket of gas or some

other feature that ultimately may have allowed enough pressure to build up to

make the mud volcano erupt. Good science on all sides of this issue have not

resolved its origin with certainty, but on the whole I think the consensus is

that the mud eruption was indeed triggered by the drilling. Studies continue,

and there are legal cases in progress too, of course.

Sidoarjo Mud Flow, Indonesia, 2008

NASA image created by Jesse Allen, using data from NASA/GSFC/METI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team. Caption by Michon Scott, based on interpretation by Geoffrey S. Plumlee, U.S. Geological Survey Crustal Imaging and Characterization Team. Source 

Another mud volcano that was recently in the news is in

Taiwan. Taiwan has at least 17 mud volcanoes which have been known for

centuries, and the flammable natural gas associated with them was used in

brick-making in southern Taiwan. The gas is probably methane, and it sometimes

ignites naturally. The Wandan mud volcano in this area has a sporadic history,

dormant for 9 years in the 1980s but erupting with damage in 2011 and 2016.

Taiwan is on the subduction zone between the Philippine plate and Eurasia,

complicated by a change in orientation of the subduction zone where Taiwan

sits. This complex tectonic setting, together with the heat liberated by

subduction, is probably the ultimate cause of the earthquakes, geologically

recent volcanism, and the mud volcanoes on Taiwan.

Mud volcano eruptions are probably no more predictable than

real volcanoes or earthquakes, but their similarity to geysers might give at

least an element of predictability to them. A mud volcano that erupted in

Trinidad in February 2018 seems to have a period of about 25 to 30 years, but

that’s obviously a pretty wide range. The most recent event at Trinidad’s

Devils Woodyard mud volcano covered an area about 100 meters across and tossed

mud six meters into the air. Like the features in Azerbaijan, the mud volcanoes

in Trinidad are closely associated with hydrocarbon deposits, including

Trinidad’s famous pitch lake – thick tarry oil at the surface of the land.

Most of the hot mud activity in Yellowstone isn’t really

what you’d call mud volcanoes. It’s more boiling mud-rich hot springs like the

Fountain Paint Pots, but every now and then they can make small cones, less

than a meter high, and in the past there have been mud-rich geyser eruptions at

Yellowstone.

By some estimates there are many more mud volcanoes on the

sea floor than there are on land. The known offshore mud volcanoes are often

associated with methane hydrates – methane gas frozen into ice in the sediment

beneath the sea floor. So it would be no surprise that as those ice-methane

complexes melt they might drive the development of mud volcanoes underwater.

—Richard I. Gibson

Links:

Smilodon and dire wolves (drawing by Robert Horsfall, 1913)

Running time, 1 hour. File size, 69 megabytes.

This is an assembly of the episodes in the original series

from 2014 that are about Cretaceous and Cenozoic vertebrates.

I’ve left the references to specific dates in the podcast so

that you can, if you want, go to the specific blog post that has links and

illustrations for that episode. They are all indexed on the right-hand side of

the blog.

Thanks for your interest and support!

Morganucodon, a possible early mammal from the Late Triassic. Length about four inches.Drawing by FunkMonk (Michael B. H.) used under Creative Commons license. 

This is an assembly of the episodes in the original series

from 2014 that are about Triassic and Jurassic vertebrates.

As usual, I’ve left the references to specific dates in the podcast so

that you can, if you want, go to the specific blog post that has links and

illustrations for that episode. They are all indexed on the right-hand side of

the blog.

Thanks for your interest and support!