The chemistry behind the new one pound coin

We all know that money makes the world go around, but do you know what goes into it? The new pound coin arrived on 28th March, largely as a preventative measure against counterfeiting.  Take a look at the graphic below for more information about its composition.

Source: Compound Interest

Why the new coin is harder to counterfeit
  1. 12-sided – its distinctive shape means it stands out by sight and by touch
  2. Bimetallic – The outer ring is gold coloured (nickel-brass) and the inner ring is silver coloured (nickel-plated alloy)
  3. Latent image – it has an image like a hologram that changes from a ‘£’ symbol to the number ‘1’ when the coin is seen from different angles
  4. Micro-lettering – around the rim on the heads side of the coin tiny lettering reads: ONE POUND. On the tails side you can find the year the coin was produced
  5. Milled edges – it has grooves on alternate sides
  6. Hidden high security feature – an additional security feature is built into the coin to protect it from counterfeiting but details have not been revealed

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New device produces hydrogen peroxide for water purification

Limited access to clean water is a major issue for billions of people in the developing world, where water sources are often contaminated with urban, industrial and agricultural waste. Many disease-causing organisms and organic pollutants can be quickly removed from water using hydrogen peroxide without leaving any harmful residual chemicals. However, producing and distributing hydrogen peroxide is a challenge in many parts of the world.

Purified drinking water
Now scientists at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have created a small device for hydrogen peroxide production that could be powered by renewable energy sources, like conventional solar panels.

“The idea is to develop an electrochemical cell that generates hydrogen peroxide from oxygen and water on site, and then use that hydrogen peroxide in groundwater to oxidize organic contaminants that are harmful for humans to ingest,” said Chris Hahn, a SLAC associate staff scientist.

Their results were reported March 1 in Reaction Chemistry and Engineering.
The project was a collaboration between three research groups at the SUNCAT Center for Interface Science and Catalysis, which is jointly run by SLAC and Stanford University.

“Most of the projects here at SUNCAT follow a similar path,” said Zhihua (Bill) Chen, a graduate student in the group of Tom Jaramillo, an associate professor at SLAC and Stanford. “They start from predictions based on theory, move to catalyst development and eventually produce a prototype device with a practical application.”

In this case, researchers in the theory group led by SLAC/Stanford Professor Jens Nørskov used computational modeling, at the atomic scale, to investigate carbon-based catalysts capable of lowering the cost and increasing the efficiency of hydrogen peroxide production. Their study revealed that most defects in these materials are naturally selective for generating hydrogen peroxide, and some are also highly active. Since defects can be naturally formed in the carbon-based materials during the growth process, the key finding was to make a material with as many defects as possible.

“My previous catalyst for this reaction used platinum, which is too expensive for decentralized water purification,” said research engineer Samira Siahrostami. “The beautiful thing about our cheaper carbon-based material is that it has a huge number of defects that are active sites for catalyzing hydrogen peroxide production.”

Stanford graduate student Shucheng Chen, who works with Stanford Professor Zhenan Bao, then prepared the carbon catalysts and measured their properties. With the help of SSRL staff scientists Dennis Nordlund and Dimosthenis Sokaras, these catalysts were also characterized using X-rays at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science User Facility.

“We depended on our experiments at SSRL to better understand our material’s structure and check that it had the right kinds of defects,” Shucheng Chen said.

Finally, he passed the catalyst along to his roommate Bill Chen, who designed, built and tested their device.

“Our device has three compartments,” Bill Chen explained. “In the first chamber, oxygen gas flows through the chamber, interfaces with the catalyst made by Shucheng and is reduced into hydrogen peroxide. The hydrogen peroxide then enters the middle chamber, where it is stored in a solution.” In a third chamber, another catalyst converts water into oxygen gas, and the cycle starts over.

Separating the two catalysts with a middle chamber makes the device cheaper, simpler and more robust than separating them with a standard semi-permeable membrane, which can be attacked and degraded by the hydrogen peroxide.

The device can also run on renewable energy sources available in villages. The electrochemical cell is essentially an electrical circuit that operates with a small voltage applied across it. The reaction in chamber one puts electrons into oxygen to make hydrogen peroxide, which is balanced by a counter reaction in chamber three that takes electrons from water to make oxygen – matching the current and completing the circuit. Since the device requires only about 1.7 volts applied between the catalysts, it can run on a battery or two standard solar panels.

The research groups are now working on a higher-capacity device.

Currently the middle chamber holds only about 10 microliters of hydrogen peroxide; they want to make it bigger. They’re also trying to continuously circulate the liquid in the middle chamber to rapidly pump hydrogen peroxide out, so the size of the storage chamber no longer limits production.

They would also like to make hydrogen peroxide in higher concentrations. However, only a few milligrams are needed to treat one liter of water, and the current prototype already produces a sufficient concentration, which is one-tenth the concentration of the hydrogen peroxide that you buy at the store for your basic medical needs.

In the long term, the team wants to change the alkaline environment inside the cell to a neutral one that’s more like water. This would make it easier for people to use, because the hydrogen peroxide could be mixed with drinking water directly without having to neutralize it first.

The team members are excited about their results and feel they are on the right track to developing a practical device.

“Currently it’s just a prototype, but I personally think it will shine in the area of decentralized water purification for the developing world,” said Bill Chen. “It’s like a magic box. I hope it can become a reality.”

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On this day in science history: polyethylene was discovered

Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while investigating diazomethane. When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance that he had created, they recognized that it contained long –CH2– chains and termed it polymethylene.

Polythylene balls, by Lluis tgn (Own work) [CC BY-SA 3.0 (http://ift.tt/HKkdTz) or GFDL (http://ift.tt/KbUOlc)%5D, via Wikimedia Commons
The first industrially practical polyethylene synthesis (diazomethane is a notoriously unstable substance that is generally avoided in industrial application) was discovered in 1933 by Eric Fawcett and Reginald Gibson, again by accident, at the Imperial Chemical Industries (ICI) works in Northwich, England.  Upon applying extremely high pressure (several hundred atmospheres) to a mixture of ethylene and benzaldehyde they again produced a white, waxy material. Because the reaction had been initiated by trace oxygen contamination in their apparatus, the experiment was, at first, difficult to reproduce. It was not until 1935 that another ICI chemist, Michael Perrin, developed this accident into a reproducible high-pressure synthesis for polyethylene that became the basis for industrial LDPE production beginning in 1939. Because polyethylene was found to have very low-loss properties at very high frequency radio waves, commercial distribution in Britain was suspended on the outbreak of World War II, secrecy imposed, and the new process was used to produce insulation for UHF and SHF coaxial cables of radar sets. During World War II, further research was done on the ICI process and in 1944 Bakelite Corporation at Sabine, Texas, and Du Pont at Charleston, West Virginia, began large-scale commercial production under license from ICI.

The breakthrough landmark in the commercial production of polyethylene began with the development of catalyst that promote the polymerization at mild temperatures and pressures. The first of these was a chromium trioxide–based catalyst discovered in 1951 by Robert Banks and J. Paul Hogan at Phillips Petroleum. In 1953 the German chemist Karl Ziegler developed a catalytic system based on titanium halides and organoaluminium compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are heavily used industrially. By the end of the 1950s both the Phillips- and Ziegler-type catalysts were being used for HDPE production. In the 1970s, the Ziegler system was improved by the incorporation of magnesium chloride. Catalytic systems based on soluble catalysts, the metallocenes, were reported in 1976 by Walter Kaminsky and Hansjörg Sinn. The Ziegler- and metallocene-based catalysts families have proven to be very flexible at copolymerizing ethylene with other olefins and have become the basis for the wide range of polyethylene resins available today, including very low density polyethylene and linear low-density polyethylene. Such resins, in the form of UHMWPE fibers, have (as of 2005) begun to replace aramids in many high-strength applications.

One of the main problems of polyethylene is that without special treatment it’s not readily biodegradable, and thus accumulates. In Japan, getting rid of plastics in an environmentally friendly way was the major problem discussed until the Fukushima disaster in 2011. It was listed as a $90 billion market for solutions. Since 2008, Japan has rapidly increased the recycling of plastics, but still has a large amount of plastic wrapping which goes to waste.

In May 2008, Daniel Burd, a 16-year-old Canadian, won the Canada-Wide Science Fair in Ottawa after discovering that Pseudomonas fluorescens, with the help of Sphingomonas, can degrade over 40% of the weight of plastic bags in less than three months.

The thermophilic bacterium Brevibacillus borstelensis (strain 707) was isolated from a soil sample and found to use low-density polyethylene as a sole carbon source when incubated together at 50°C. Biodegradation increased with time exposed to ultraviolet radiation.

In 2010, a Japanese researcher, Akinori Ito, released the prototype of a machine which creates oil from polyethylene using a small, self-contained vapor distillation process.

In 2014, a Chinese researcher discovered that Indian mealmoth larvae could metabolize polyethylene from observing that plastic bags at his home had small holes in them. Deducing that the hungry larvae must have digested the plastic somehow, he and his team analyzed their gut bacteria and found a few that could use plastic as their only carbon source. Not only could the bacteria from the guts of the Plodia interpunctella moth larvae metabolize polyethylene, they degraded it significantly, dropping its tensile strength by 50%, its mass by 10% and the molecular weights of its polymeric chains by 13%.

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Why water splashes: New theory reveals secrets

New research from the University of Warwick generates fresh insight into how a raindrop or spilt coffee splashes.

Dr James Sprittles from the Mathematics Institute has created a new theory to explain exactly what happens – in the tiny space between a drop of water and a surface – to cause a splash.

Water splash

When a drop of water falls, it is prevented from spreading smoothly across a surface by a microscopically thin layer of air that it can’t push aside – so instead of wetting the surface, parts of the liquid fly off, and a splash is generated.

A layer of air 1 micron in size – fifty times smaller than the width of a human hair – can obstruct a 1mm drop of water which is one thousand times larger.

This is comparable to a 1cm layer of air stopping a tsunami wave spreading across a beach.

Dr Sprittles has established exactly what happens to this miniscule layer of air during the super-fast action by developing a new theory, capturing its microscopic dynamics – factoring in different physical conditions, such as liquid viscosity and air pressure, to predict whether splashes will occur or not.

The lower the air pressure, the easier the air can escape from the squashed layer – giving less resistance to the water drop – enabling the suppression of splashes. This is why drops are less likely to splash at the top of mountains, where the air pressure is reduced.

Understanding the conditions that cause splashing enables researchers to find out how to prevent it – leading to potential breakthroughs in various fields.

In 3D printing, liquid drops can form the building blocks of tailor-made products such as hearing aids; stopping splashing is key to making products of the desired quality.

Splashes are also a crucial part of forensic science – whether blood drops have splashed or not provides insight into where they came from, which can be vital information in a criminal investigation.

Dr Sprittles comments:

“You would never expect a seemingly simple everyday event to exhibit such complexity. The air layer’s width is so small that it is similar to the distance air molecules travel between collisions, so that traditional models are inaccurate and a microscopic theory is required.

“Most promisingly, the new theory should have applications to a wide range of related phenomena, such as in climate science – to understand how water drops collide during the formation of clouds or to estimate the quantity of gas being dragged into our oceans by rainfall.”

The research, ‘Kinetic Effects in Dynamic Wetting’, is published in Physical Review Letters.

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Looking for signs of the first stars

It may soon be possible to detect the universe’s first stars by looking for the blue colour they emit on explosion.

The universe was dark and filled with hydrogen and helium for 100 million years following the Big Bang. Then, the first stars appeared, and metals were created by thermonuclear fusion reactions within stars.

Stars in the sky, ESA/Hubble [CC BY 4.0 (http://ift.tt/1eRPUFd)%5D, via Wikimedia Commons
These metals were spread around the galaxies by exploding stars or ‘supernovae’. Studying first-generation supernovae, which are more than 13 billion years old, provides a glimpse into what the universe might have looked like when the first stars, galaxies and supermassive black holes formed. But to-date, it has been difficult to distinguish a first-generation supernova from a later one.

New research, led by Alexey Tolstov from the Kavli Institute for the Physics and Mathematics of the Universe, has identified characteristic differences between these supernovae types after experimenting with supernovae models based on observations of extremely metal-poor stars.

Similar to all supernovae, the luminosity of metal-poor supernovae shows a characteristic rise to a peak brightness followed by a decline. The phenomenon starts when a star explodes with a bright flash, caused by a shock wave emerging from its surface after its core collapses. This is followed by a long ‘plateau’ phase of almost constant luminosity lasting several months, followed by a slow exponential decay.

The team calculated the light curves of metal-poor blue versus metal-rich red supergiant stars. The shock wave and plateau phases are shorter, bluer and fainter in metal-poor supernovae. The team concluded that the colour blue could be used as an indicator of a first-generation supernova. In the near future, new, large telescopes, such as the James Webb Space Telescope scheduled to be launched in 2018, will be able to detect the first explosions of stars and may be able to identify them using this method.

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The chemistry behind the ‘Oscar’

A BIT of a mix up might have dinted the magical chemistry of the Oscars this year, but it didn’t damage the sheen on those golden statuettes! 


So, what exactly IS the chemistry behind the world’s most famous prize? Check out the graphic below to learn exactly WHAT goes into an Oscar statuette. 

Source: Compound Interest

So, who knew the statuette wasn’t made from REAL gold? And what is the history of Britannium? First produced in 1769 or 1770, Britannium metal was created by James Vickers after purchasing the formula from a dying friend. It was originally known as “Vickers White Metal” when made under contract by the Sheffield manufacturers Ebenezer Hancock and Richard Jessop. In 1776 James Vickers took over the manufacturing himself and remained as owner until his death in 1809, when the company passed to his son, John, and Son-in-Law, Elijah West. In 1836 the company was sold to John Vickers’s nephew Ebenezer Stacey (the son of Hannah Vickers and John Stacey).

After the development of electroplating with silver in 1846, Britannia metal was widely used as the base metal for silver-plated household goods and cutlery. The abbreviation EPBM on such items denotes “electroplated Britannia metal”. Britannia metal was generally used as a cheaper alternative to electroplated nickel silver (EPNS) which is more durable.

In his essay, A Nice Cup of Tea, writer George Orwell asserts that “britanniaware” teapots “produce inferior tea” (when compared to Chinaware).


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On this day in science history: Sakurai’s Object was discovered

In 1996, a bright “new” star was discovered in Sagittarius
by Japanese amateur astronomer Yukio Sakurai. It was found not to be a usual
nova, but instead was a star going through a dramatic evolutionary state,
re-igniting its nuclear furnace for one final blast of energy called the “final
helium flash.” It was only the second to be identified in the twentieth
century. A star like the Sun ends its active life as a white dwarf star
gradually cooling down into visual oblivion. Sakurai’s Object had a mass a few
times that of the Sun. Its collapse after fusing most of its hydrogen fuel to
helium raised its temperature so much higher it began nuclear fusion of its
helium remains. This was confirmed using its light spectrum to identify the
elements present.

Sakurai’s Object By ESO, [CC BY 4.0 (http://ift.tt/1eRPUFd)%5D, via Wikimedia Commons
Sakurai’s Object is a highly evolved post-asymptotic giant
branch star which has, following a brief period on the white dwarf cooling
track, undergone a helium shell flash (also known as a very late thermal
pulse). The star is thought to have a mass of around 0.6 M☉.
Observations of Sakurai’s Object show increasing reddening and pulsing
activity, suggesting that the star is exhibiting thermal instability during its
final helium-shell flash.

Prior to its reignition V4334 Sgr is thought to have been cooling
towards a white dwarf with a temperature around 100,000 K and a luminosity
around 100 L☉. The luminosity rapidly increased about a
hundred-fold and then the temperature decreased to around 10,000 K. The star
developed the appearance of an F class supergiant (F2 Ia). The apparent
temperature continued to cool to below 6,000 K and the star was gradually
obscured at optical wavelengths by the formation of carbon dust, similar to an
R CrB star. Since then the temperature has increased to around 20,000 K.

The properties of Sakurai’s Object are quite similar to that
of V605 Aquilae. V605, discovered in 1919, is the only other known star
observed during the high luminosity phase of a very late thermal pulse, and
Sakurai’s Object is modeled to increase in temperature in the next few decades
to match the current state of V605.

During the second half of 1998 an optically thick dust shell
obscured Sakurai’s Object, causing a rapid decrease in visibility of the star,
until in 1999 it disappeared from optical wavelength observations altogether.
Infrared observations showed that the dust cloud around the star is primarily
carbon in an amorphous form. In 2009 it was discovered that the dust shell is
strongly asymmetrical, as a disc with a major axis oriented at an angle of
134°, and inclination of around 75°. The disc is thought to be growing more
opaque due to the fast spectral evolution of the source towards lower
temperatures.

Sakurai’s Object is surrounded by a planetary nebula created
following the star’s red giant phase around 8300 years ago. It has been
determined that the nebula has a diameter of 44 arcseconds and expansion
velocity of roughly 32 km/s.

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Dwarf star 200 light years away contains life’s building blocks

Many scientists believe the Earth was dry when it first formed, and that the building blocks for life on our planet – carbon, nitrogen and water – appeared only later as a result of collisions with other objects in our solar system that had those elements.

Today, a UCLA-led team of scientists reports that it has discovered the existence of a white dwarf star whose atmosphere is rich in carbon and nitrogen, as well as in oxygen and hydrogen, the components of water. The white dwarf is approximately 200 light years from Earth and is located in the constellation Boötes.

The Earth seen from Apollo 17. By NASA/Apollo 17 crew; taken by either Harrison Schmitt or Ron Evans [Public domain or Public domain], via Wikimedia Commons

Benjamin Zuckerman, a co-author of the research and a UCLA professor of astronomy, said the study presents evidence that the planetary system associated with the white dwarf contains materials that are the basic building blocks for life. And although the study focused on this particular star – known as WD 1425+540 – the fact that its planetary system shares characteristics with our solar system strongly suggests that other planetary systems would also.

“The findings indicate that some of life’s important preconditions are common in the universe,” Zuckerman said.

The scientists report that a minor planet in the planetary system was orbiting around the white dwarf, and its trajectory was somehow altered, perhaps by the gravitational pull of a planet in the same system. That change caused the minor planet to travel very close to the white dwarf, where the star’s strong gravitational field ripped the minor planet apart into gas and dust. Those remnants went into orbit around the white dwarf – much like the rings around Saturn, Zuckerman said – before eventually spiraling onto the star itself, bringing with them the building blocks for life.

The researchers think these events occurred relatively recently, perhaps in the past 100,000 years or so, said Edward Young, another co-author of the study and a UCLA professor of geochemistry and cosmochemistry. They estimate that approximately 30 percent of the minor planet’s mass was water and other ices, and approximately 70 percent was rocky material.

The research suggests that the minor planet is the first of what are likely many such analogs to objects in our solar system’s Kuiper belt. The Kuiper belt is an enormous cluster of small bodies like comets and minor planets located in the outer reaches of our solar system, beyond Neptune. Astronomers have long wondered whether other planetary systems have bodies with properties similar to those in the Kuiper belt, and the new study appears to confirm for the first time that one such body exists.

White dwarf stars are dense, burned-out remnants of normal stars. Their strong gravitational pull causes elements like carbon, oxygen and nitrogen to sink out of their atmospheres and into their interiors, where they cannot be detected by telescopes.

The research, published in the Astrophysical Journal Letters, describes how WD 1425+540 came to obtain carbon, nitrogen, oxygen and hydrogen. This is the first time a white dwarf with nitrogen has been discovered, and one of only a few known examples of white dwarfs that have been impacted by a rocky body that was rich in water ice.

“If there is water in Kuiper belt-like objects around other stars, as there now appears to be, then when rocky planets form they need not contain life’s ingredients,” said Siyi Xu, the study’s lead author, a postdoctoral scholar at the European Southern Observatory in Germany who earned her doctorate at UCLA.

“Now we’re seeing in a planetary system outside our solar system that there are minor planets where water, nitrogen and carbon are present in abundance, as in our solar system’s Kuiper belt,” Xu said. “If Earth obtained its water, nitrogen and carbon from the impact of such objects, then rocky planets in other planetary systems could also obtain their water, nitrogen and carbon this way.”

A rocky planet that forms relatively close to its star would likely be dry, Young said.

“We would like to know whether in other planetary systems Kuiper belts exist with large quantities of water that could be added to otherwise dry planets,” he said. “Our research suggests this is likely.”

According to Zuckerman, the study doesn’t settle the question of whether life in the universe is common.

“First you need an Earth-like world in its size, mass and at the proper distance from a star like our sun,” he said, adding that astronomers still haven’t found a planet that matches those criteria.

The researchers observed WD 1425+540 with the Keck Telescope in 2008 and 2014, and with the Hubble Space Telescope in 2014. They analyzed the chemical composition of its atmosphere using an instrument called a spectrometer, which breaks light into wavelengths. Spectrometers can be tuned to the wavelengths at which scientists know a given element emits and absorbs light; scientists can then determine the element’s presence by whether it emits or absorbs light of certain characteristic wavelengths. In the new study, the researchers saw the elements in the white dwarf’s atmosphere because they absorbed some of the background light from the white dwarf.

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What makes popcorn pop? The chemistry of popcorn

We’ve all scoffed it in the cinema, but have you thought about the chemistry behind it?  Take a look at the graphic below to find out more about the compounds that give popcorn its flavour and aroma, as well as what makes it pop!

Source: Compound Interest 
So that’s the science! But what about the history of popcorn? 

Corn was first domesticated in Mexico 9,000 years ago.  Archaeologists have discovered that people have known about popcorn for thousands of years. In Mexico, for example, they’ve found remnants of popcorn that dates to around 3600 BC. Many historians even believe that popcorn is the first corn that humans even knew about. Popping of the kernels was achieved manually through the 19th century, being sold on the east coast of the USA under names such as ‘Pearls’ or ‘Nonpareil’. The term ‘popped corn’ first appeared in John Russell Bartlett’s 1848 Dictionary of Americanisms. Popcorn is an ingredient in Cracker Jack, and in the early years of the product, it was popped by hand. 

Popcorn’s accessibility increased rapidly in the 1890s with Charles Cretors’ invention of the popcorn maker. Cretors, a Chicago candy store owner, created a number of steam powered machines for roasting nuts, and applied the technology to the corn kernels. By the turn of the century, Cretors had created and deployed street carts equipped with steam powered popcorn makers.

During the Great Depression, popcorn was fairly inexpensive at 5–10 cents a bag and became popular. Thus, while other businesses failed, the popcorn business thrived and became a source of income for many struggling farmers, including the Redenbacher family, namesake of the famous popcorn brand. During World War II, sugar rations diminished candy production, and Americans compensated by eating three times as much popcorn as they had before. The snack was popular at heaters, much to the initial displeasure of many of the theatre owners, who thought it distracted from the films. Their minds eventually changed, however, and in 1938 a Midwestern theatre owner named Glen W. Dickson installed popcorn machines in the lobbies of his theatres. The venture was a financial success, and the trend soon spread.

In 1970, Orville Redenbacher’s namesake brand of popcorn was launched. In 1981, General Mills received the first patent for a microwave popcorn bag, with popcorn consumption seeing a sharp increase by tens of thousands of pounds in the years following.

At least six localities (all in the Midwestern United States) claim to be the “Popcorn Capital of the World;”: Ridgway, Illinois; Valparaiso, Indiana; Van Buren, Indiana; Schaller, Iowa; Marion, Ohio; and North Loup, Nebraska. According to the USDA, corn used for popcorn production is specifically planted for this purpose; most is grown in Nebraska and Indiana, with increasing area in Texas.

As the result of an elementary school project, popcorn became the official state snack food of Illinois.

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On this day in science history: the world’s tallest geyser was discovered

In 1901, the world’s tallest geyser was discovered by Dr Humphrey Haines on the North Island of New Zealand. He was following up reports of great clouds of steam, and found the Waimangu Geyser near Rotorua. It appeared after an enormous eruption of Mt. Tarawera in 1886. The Waimangu Geyser was the largest geyser in the world and erupted on a 36 hour cycle for four years, hurling black mud and rocks in the air. Waimangu is Maori for “black water.” It stopped in 1904 when a landslide changed the local water table. Eruptions would typically reach 600 feet. Some superbursts are known to have reached 1,600 feet (10 times as high as Yellowstone’s famous Old Faithful, and which would be higher than the Empire State Building.)

Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma. The geothermally heated water then rises back toward the surface by convection through porous and fractured rocks. Geysers differ from non-eruptive hot springs in their subterranean structure; many consist of a small vent at the surface connected to one or more narrow tubes that lead to underground reservoirs of water and pressure tight rock.

Steamboat Geyser in Yellowstone. By Brocken Inaglory (Own work) [CC BY-SA 3.0 (http://ift.tt/HKkdTz) or GFDL (http://ift.tt/KbUOlc)%5D, via Wikimedia Commons
As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is impossible. The cooler water above presses down on the hotter water beneath, not unlike the lid of a pressure cooker, allowing the water in the reservoir to become superheated, i.e. to remain liquid at temperatures well above the standard-pressure boiling point.

Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins which forces steam bubbles to rise to the top of the column. As they burst through the geyser’s vent, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water below. With this release of pressure, the superheated water flashes into steam, boiling violently throughout the column. The resulting froth of expanding steam and hot water then sprays out of the geyser vent.

A key requirement that enables a geyser to erupt is a material called geyserite found in rocks nearby the geyser. Geyserite—mostly silicon dioxide (SiO2), is dissolved from the rocks and gets deposited on the walls of the geyser’s plumbing system and on the surface. The deposits make the channels carrying the water up to the surface pressure-tight. This allows the pressure to be carried all the way to the top and not be leaked out into the loose gravel or soil that are normally under the geyser fields.

Eventually the water remaining in the geyser cools back to below the boiling point and the eruption ends; heated groundwater begins seeping back into the reservoir, and the whole cycle begins again. The duration of eruptions and time between successive eruptions vary greatly from geyser to geyser; Strokkur in Iceland erupts for a few seconds every few minutes, while Grand Geyser in the United States erupts for up to 10 minutes every 8–12 hours.

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