The Earth Story

The Driest Place on Earth.

It's not where you expect. You're thinking of majestic sand dunes along the western edge of the Sahara, or the barren rocky outcrop's of Chile's Atacama desert. The driest place on Earth is in Antarctica: the McMurdo Dry Valleys. Antarctica has been covered in ice for the last 15 million years, and has built up an average ice thickness of 1.9km. The entire continent is cold (as low as -90ºC) and as dry as most deserts on Earth (South Pole average precipitation is 10cm/year). The McMurdo Dry Valleys are even drier. The fact that they have remained ice free, while the rest of the continent has built up thousands of meters of ice over millions of years, tells you just how parched these valleys are.

Their annual average precipitation is zero cm. They are found in the rain shadow of the 1.6km high Transantarctic Mountains. These mountains also act as a barrier to prevent glaciers from flowing into the valleys. Any ice that does form in the valleys rapidly 'sublimates', evaporating directly from solid ice to water vapour without melting. This processes is helped along by bone-dry 'katabatic winds', which form as cold dense air literally falls off the surrounding ice sheets, and rips through the valleys at over 300 km per hour.

Animals that stray too far into the valleys quickly die of dehydration. Rather than rotting, the dry air desiccates and mummifies their bodies, which can be preserved on the valley floor for hundreds or thousands of years (like the seal in the photo). When the explorer Robert Scott discovered these valleys in 1903, he called them the 'valleys of death'.

Since 1903 scientists have had a closer look at the dry valleys, and they are far from dead. All kinds of 'extremophiles' (life that thrives in extreme environments) call the McMurdo valleys home - lichens, mosses, nematodes (microscopic worms) and other microbes are most common.

These frozen deserts are one of the best analogues we have for Martian environments. Studying how life survives there is one of our best ways of understanding how life might exist on other planets.

Image Source: - Bull Pass: http://goo.gl/E15f19 - Mumified Seal: http://goo.gl/TtIoqe

Where are these dry valleys?: http://goo.gl/CCnTSd A bit more about them: http://goo.gl/Mj1ZvU The wettest place on Earth: http://goo.gl/7Ge5lE We've talked about these valleys before: http://goo.gl/pAHkY9

A geologist's breakfast? Fry ups are an essential part of field cooking, where getting plenty calories in with minimum time and effort is a way of life. These amazing speleothems called fried egg form in caves when slightly acidic water is forced to precipitate some of its mineral content (in this case calcium carbonate deposited as calcite) when it encounters a change in conditions. This particular example is from Luray Caverns in Virginia and could be a wonderful way to start one's day spelunking. Loz Image credit: Abraham S

Let it snow, let it snow, let it snow!

There are few things more beautiful than the intricacy of a snowflake, but how exactly are they formed? Why are they symmetrical? Why are no two the same?

Let’s find out!

The birth of a snowflake:

Snowflakes form in cold weather when water droplets in the atmosphere freeze onto a particulate; perhaps pollen or some dust. As the particle has now gained a bit of weight (don’t we all over the holidays?), it begins to fall towards the ground. As the ice crystal is falling, water vapour freezes onto it, building new crystals and laying the foundation for a snow flake to form. The temperature at which a crystal forms and the humidity of the air determines the basic shape of the ice crystal. For example, we tend to see long needle-like crystals at -2 degrees C and very flat plate-like crystals at -15 degrees C.

Symmetry!

Many snowflakes are symmetrical; this is due to the crystallisation of water molecules. When water molecules are in a solid state, such as in ice and snow, they form weak bonds (called hydrogen bonds) with one another. This process means that they arrange themselves in predetermined spaces which results in the symmetrical, hexagonal shape of the snowflake.

No two the same?

If you take into account the number of water molecules and isotopes of oxygen and hydrogen, then it is safe to say that no two snowflakes are identical. However, it is possible to find two that look pretty similar, but even this is a huge improbability- I definitely wouldn't recommend spending your life trying to find snowflake twins!

When you think about it, each snowflake will follow a slightly different path through the atmosphere and will encounter different conditions along its journey; so they all tend to look unique- more diversity to awe at!

-Jean

Images courtesy of Alexey Kljatov

This clip explores the growth of solid substances by precipitation in timelapse view. Many of these occur in nature and thus these are also the ways actual minerals grow. Iron hydroxides are the material that coats rivers in Acid Mine Drainage. Barium sulfate is the mineral barite. Watch how these things grow in all sorts of directions - growth controlled by which direction of the substance grows the fastest in these media.

Rain in the sky and topography

Sahara Snow

Snow is probably not the first thing that comes to mind when you hear someone mention the Sahara Desert. The Sahara is known for its sweltering heat, but on Monday it snowed near the town of Ain Sefra, Algeria; the first recorded snowfall there since February 1979.

The Sahara is the second-largest desert (Antarctica is first) on Earth at about 8,600,000 square kilometers (3,320,000 square miles); large enough to fill nearly all of northern Africa. The topography varies quite a bit over that expanse. Ain Sefra is at an elevation of 1,081 meters (3,547 feet), high enough to experience nighttime winter temperatures near, but usually above, freezing. Monday the temperature was well below average, enough to drop it below the freezing point even during the day.

Since it’s a desert there isn’t a lot of precipitation, but some moisture does fall on average each month, and the conditions happened to be right on Monday for it to fall as snow. A strong low pressure system passed over the area and forced the air to rise and cool rapidly, resulting in snowfall. The snow on the ground only lasted about a day, just long enough to get some amazing photos.

Photo Credit: Karim Bouchetata https://www.facebook.com/kbouchetata

References: http://wapo.st/2igh2rd https://www.britannica.com/place/Sahara-desert-Africa

Wormy

This is a microscopic image of a myrmekitic feldspar. This wormy texture is a single, 2 millimeter grain of plagioclase that has had strings of the mineral quartz grow throughout it. There are a number of different proposed mechanisms by which myrmekite can form, all of which probably do happen.

This crystal of plagioclase probably represents a mechanism involving strain, perhaps even fracturing or bending of the crystal during strain and metamorphism. Once a crack has formed in a crystal, metamorphic fluids can get into the structure. Fluids flowing along a crack will find a protected, lower-pressure environment where dissolved elements such as silica can precipitate. These now-filled cracks appear as worms filled with newly-grown, metamorphic quartz.

-JBB

Image credit: http://bit.ly/2fHSAyW Reference: http://www.minsocam.org/ammin/AM71/AM71_895.pdf http://bit.ly/2eTq5ja http://link.springer.com/article/10.1007/s00410-014-1074-7 http://www.perplex.ethz.ch/papers/cesare_jmg_2002.pdf

Vanished Lake Lahontan

A goodly chunk of western Nevada was once a lake, hard to believe when we see it in its current desertic state. Lake Lahontan was formed of several interconnected lakes between ranges of mountains, mostly formed by the extensional faulting that is shaping the Basin and Range province. As the climate warmed and dried, the glaciers that helped feed the lake melted and the climate became more arid, reducing rainfall. The lake gradually evaporated and split into several new lakes as the water level lowered.

Most of its remnant arms are now playas, containing flat salty sediments enclosed by mountains. At its peak it filled most of western Nevada and parts of California covering 21,000 square kilometres and was one of north America's largest lakes. Lahontan was a pluvial lake, which form in enclosed basins without through drainage. They have fluctuating water levels, which oscillate in response to changes in climate. . Being enclosed, if precipitation falls below evaporation, they swiftly disappear. When Lahontan existed, rainfall was higher and evaporation much lower than today, but by 9,000 BCE it had more or less vanished as the ice age ended. The first Americans appeared in the area while the lake still existed.

This image is of Pyramid Lake, which along with Lake Walker, is one of the two year round remnants of what was once a huge body of water. It was once Lahontan's deepest point (about 270 Metres). The white deposits visible in the picture are tufa, a form of calcium carbonate that precipitates from fresh water. These formations delineate the paleo lake level throughout the region.

Loz

Image credit: NASA http://visibleearth.nasa.gov/view.php?id=46402 http://visibleearth.nasa.gov/view.php?id=78892 Paleomap of the lake: http://pubs.usgs.gov/mf/1999/mf-2323/mf2323.pdf http://www.uwec.edu/jolhm/Past_Classes/1998/491Class/Nov7/history.htm

Phantoms

The Borg cube like mass of interpenetrant crystals is made of calcite, just like stalactites and other formations in caves. Precipitated slowly out of calcium carbonate rich waters the crystals developed good transparency, but at the very end of their growth the waters started to contain an admixture of dissolved iron, which precipitated as small inclusions of the reddish orange iron oxide mineral haematite (see http://bit.ly/2ctVrsX) outlining their edges in a scene of near perfect beauty. The specimen comes from the Tsumeb mine in Namibia (see http://bit.ly/1c2CjkD) and measures 7 x11 x 5.7 cm.

Loz

Image credit: Exceptional Minerals

An aerial river

California and the Sierras finally got some much needed rain and snow last week, though nowhere near enough to restore the hydric resources depleted by the ongoing multi year drought. The drought has been cause by a blocking pattern in the jet stream that deviated the atmospheric river (see http://on.fb.me/21Zs2LX for an explanation of what these are and their role in weather) that normally brings winter rains to the American West coast. Whether the pattern is going to provide further rains or not remains to be seen, the NOAA got a stunning satellite shot of the Pineapple Express river coasting northeast across the Pacific, carrying the moisture evaporated in the tropics near Hawaii towards the cooler northern climes, where it dumps its water when it encounters the hills of California, rises, cools and condenses into raindrops.

Loz

Satellite video of this event: http://tmblr.co/Zyv2Js1zoG7IM Image credit: NOAA http://1.usa.gov/1NW1SWb

This amazing 3-D animated gif was produced by NASA scientists using data from the GPM satellite. It shows cloud structures and precipitation rates (colors show intensity of precipitation) in Tropical Storm Kilo, which may impact Hawaii this week. 

CLOUD SEEDING

No, this post is not about ‘chemtrails’. Cloudseeding is a real technique, and is used to induce rain or snow in clouds. This is usually achieved by dropping particular particles into clouds that contain supercooled water, to try to cause the clouds to dissipate, modify their structure or alter the intensity of phenomena like wind speed or hail. Cloud seeding can be done by ground generators, plane, or rocket.

Natural rainfall occurs when supercooled cold water interacts with particles of dust salt or sand and forms ice crystals. These ice crystals then form a nucleus; more water droplets can then attach themselves to this nucleus and increase the size of the droplet (in colder air these droplets are snowflakes). When this droplet or snow flake reaches a critical size it falls as snow or rain.

The idea of cloudseeding started in 1946, when Dr. Vincent J. Schaefer (who was working at the General Electric Laboratory in New York), was researching how to create artificial clouds in a chilled chamber. Schaefer added dry ice to one experiment, to cool the chamber further. The water vapour in the chamber formed a cloud around this dry ice; the ice crystals in the dry ice had created a nucleus around which droplets of water could now form. This process is known as the cold rain process.

Cloud seeding increases the number of the nuclei available so to take greater advantage of the moisture in the cloud, forming raindrops that would not normally have formed.

The warm rain process involves clouds in tropical regions that never reach freezing point. In these cases, raindrops form around a hygroscopic nucleus, which is a particle like salt or dust that attracts water. Small droplets collide and amalgamate until they form a droplet large enough to fall. Another type of cloudseeding, dynamic cloud seeding, aims to boost vertical air currents; this encourages more water to pass through the clouds, which in turn leads to more rain.

To encourage the warm rain process, calcium chloride is commonly used to provide the nucleus for raindrop formation. For the cold rain process, silver-iodide (introduced either via the air or the ground) can be used as a nuclei; its structure is very similar to ice crystals. Dry ice can be introduced from the air (at -80°C) into clouds; this lowers the air temperature so that some of the supercooled water droplets can be converted into ice crystals.

Common salt or fine water droplets can also be used to encourage coalescence. Most of the methods that are used to limit the development of hail use cloud seeding that employs ice nucleants, or use silver oxide. Hail damage can in theory be reduced by 25% by using cloud seeding; there have been no quantifiable results demonstrating this however.

CSIRO conducted cloudseeding trials in Australia between 1947 and the early 1960s. Only the trial conducted in the Snowy Mountains during the late 1950’s and the early 1960’s produced any statistically significant rainfall increases. The Queensland government of Australia announced in December 2006 $7.6 million in funding for "warm cloud" seeding research.

Clouds were seeded during the 2008 Summer Olympics in Beijing using rockets, to guarantee there would be no rain during the opening and closing ceremonies. In the United States, cloud seeding is used to increase rainfall in areas experiencing drought, to reduce the size of hailstones that form in thunderstorms, and also to reduce the amount of fog in and around airports. It is also sometimes used by ski resorts to induce snowfall. After the Chernobyl disaster, Soviet military pilots seeded clouds over the Belorussian SSR to remove radioactive particles from clouds heading toward Moscow. Cloud seeding is used on a national scale in Mali and Niger.

Diagrams explaining cloud seeding: http://bit.ly/Wcb3ap; http://bit.ly/ZsiszE

The image shows a proposed cloud-seeding ship with Flettner rotors that spin about their vertical axis and act as powerful computer-controlled sails. Seawater sprays from the tops of the rotors to seed clouds. According to theory and computer models, seeding marine stratocumulus clouds by spraying them with an ultrafine saltwater mist from ships could significantly enhance cloud droplet number concentration. The clouds, containing more particles, would cast enough sunlight back into space to at least partially offset the warming effects of CO2 from burning fossil fuels (http://bit.ly/VFV8ia).

-TEL

http://www.weatheronline.co.uk/reports/wxfacts/Cloud-seeding.htm http://science.howstuffworks.com/nature/climate-weather/meteorologists/cloud-seeding1.htm http://www.telegraph.co.uk/news/worldnews/1549366/How-we-made-the-Chernobyl-rain.html http://media01.couriermail.com.au/multimedia/2007/03/070300-water/story6-1.html http://www.source.irc.nl/page/10355 http://www.scientificamerican.com/article.cfm?id=albedo-yachts-and-marine-clouds

Image: ©John MacNeil Illustration

6 months of rainfall

In 2014, the U.S. and Japan combined to launch the Global Precipitation Measurement (GPM) satellite, a system that would use high-tech radar instruments to constantly measure the amount of precipitation falling across the entire globe.

That satellite will give scientists enormous ability to monitor how the Earth’s surface interacts with the atmosphere. Rather than reconstructing rainfall patterns from individual measurements, GPM can show exactly where rain falls, how much rain hits a site, and how those patterns change from year to year. Its information can be used to answer important questions like “How much rainfall does it take for erosion to happen in this area” or “what patterns are linked to the early development of drought conditions”.

On top of the great information it returns, the 3-D visualizations of weather patterns it is producing really are spectacular. This video shows GPM-measured precipitation across the U.S. for the first 6 months of 2015 (up to July 15); areas in red have received over 100 cm of rainfall, areas in purple have received about 200 cm or more. You can see swaths of heavy rainfall in Illinois and Louisiana, in addition to the huge rains that struck Texas and Oklahoma in May. You can also see the stark difference between the two sides of the continent; basically everything to the west is in moderate to exceptional drought conditions while much of the east has gotten ample rainfall.

-JBB

Video Credit: NASA/NOAA/GSFC http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4337 Drought monitor: http://droughtmonitor.unl.edu Other visualizations: http://tmblr.co/Zyv2Js1epdVwH http://tmblr.co/Zyv2Js1nizmv5 http://tmblr.co/Zyv2Js1ea1OTD

How do ice cores preserve temperature records?

Cores drilled through the icecaps in Greenland and Antarctica are our best records of the climate over the last 800,000 years. The best cores literally have 1 band of ice per year, so the ice in each core can be precisely dated. The chemistry of the ice can then show whether there were glaciers present or not….but how do geochemists do that?

Interpreting these records is done in part using isotopes of oxygen and hydrogen. Isotopes are atoms that have the same number of protons and electrons but different numbers of neutrons. For example, hydrogen has 0 neutrons and deuterium has 1 neutron, giving deuterium twice the mass of normal hydrogen.

For the most part, different isotopes of one element behave the same. Deuterium will still bond with oxygen to make water just like hydrogen will. However, there are some very subtle properties that vary between the different isotopes. For example, when water evaporates, heavier isotopes prefer to stay in the liquid rather than going into the gas.

This effect is so small that the units on isotope plots often are this funny “per mille” unit – permille is 10 times smaller than a percent. On a plot like this one, negative values mean that the measured sample is missing the heavy isotope relative to the standard, which is usually seawater.

Both hydrogen and oxygen have heavy isotopes and glacial ice is very low in those heavy isotopes relative to ocean water today (hence the very negative numbers), but as you can see there’s also a pattern. The glacial ice gets more heavy hydrogen and heavy oxygen at the same time, and 120,000 years ago there was a measureable spike in both.

What does it mean for snow at the poles to have more heavy isotopes? That’s how we turn this record into information about temperature.

The ratio of the heavy and light isotopes in water vapor evaporated from the ocean depends on the temperature of the oceans. If the oceans are cooler, any water that evaporates is missing even more of its heavy isotopes.

On top of that, the colder the planet is, the less humid it is. When the atmosphere is less humid, it’s easier for any water that does evaporate to rain out at low latitudes, so even less moisture makes it to the poles. Again the same rule applies – heavy isotopes go into the liquid, so by the time those last slivers of moisture make it to the poles, they’re missing even more of the heavy isotopes. Other factors, such as the temperature of the atmosphere where the snow forms and the altitude the snow forms at, play in as well, and all those can be calibrated and measured.

Overall, on this plot, the more negative the values are, the greater the volume of the ice sheets and the colder the planet.

When the values spike upwards, we see evidence that the ice sheets shrank, including dumping of extra sediment in the oceans from icebergs breaking off the edges. When we take this type of data back in time, we can see that the Earth has been locked in a cyclic pattern – large glaciers advance, grow for about 100,000 years with a few breakups in-between, then break up fully and start reforming after a few thousand years. The chemistry of the H2O locked in ice cores therefore tells us the story of how glaciers advanced and retreated over the past 800,00 years.

By understanding these changes as recorded by these cores of ice, we can begin to ask the all-important question for scientists…”Why did this happen”, and then start to assess what that means for changes happening today.

-JBB

Image credit: http://bit.ly/1ISmarl

Read more: http://bit.ly/1LXIaE8 http://cdiac.ornl.gov/trends/co2/ice_core_isotopes.html

Fly through Bill

This week, Tropical Storm Bill slipped across the Gulf of Mexico shoreline and marched north, dropping copious amounts of rain on the state of Texas while the state was just trying to recover from the severe flooding during May. Although many of our readers have had an experience with Bill directly, this video will give a view you haven’t seen elsewhere; you can fly through Bill as it develops.

Bill wasn’t a powerful storm in terms of winds but it had a lot of moisture. It moved slowly across Texas with rain bands stalling over several areas, migrated across the central United States, and is actually making it rain on me today. It hung together as a tropical depression with an organized center across several states, actually feeding off moisture from the recent rains in Texas and Oklahoma to keep itself strong longer, a phenomenon nicknamed the “Brown Ocean” effect (http://on.fb.me/1L3N3gA).

This video flies through Bill early in its time over land, while it was still crossing Texas and Louisiana. Last year, the United States launched the Global Precipitation Measuring (GPM) satellite, carrying microwave and radar detectors that actually let the satellite peer through the clouds and into a storm; this data comes from that satellite.

You can watch as clouds develop into vertical columns that dump moisture down, you can see the boundary between the clouds and the rainfall, you can even see how some areas get more intense rainfall than others. All that can be mapped out by this satellite.

By measuring rainfall this way, scientists can actually see things like the brown ocean effect as it develops. Rather than just measuring rainfall at specific points on the ground, the full breadth of a storm can be monitored. Given that data, scientists will be able to better model future storms and how they will impact weather and flood risk when they move ashore.

The GPM satellite was the successor to a previous mission, the Tropical Rainfall Measuring Mission (TRMM), which could take those measurements in a more limited way and only traveled above the tropics. It couldn’t have seen Tropical Storm Bill. Its data, however, shapes the way we think about storm development in the tropics and how we think about rainfall variations across continents. TRMMs mission ended last year as it ran out of fuel and actually it fell to earth on Thursday – the very same day this GPM data was collected.

-JBB

Video credit: Nasa scientific visualization studio https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4316 Read more: http://www.space.com/29676-falling-nasa-satellite-trmm-burn… http://bit.ly/1GkrqT3

In 2000 and 2010, NOAA, the National Oceanographic and Atmospheric Administration, released guidelines for planting based on the average temperature and rainfall across the country. To simplify things, different plant zones are grouped into simple numbers 1-10. This gif courtesy of NOAA shows how those belts have migrated north over the last decade as temperatures and rainfall patterns have changed.