Guest Post by Steven Goddard
The Guardian image below taken this week near Iceland has the caption “Smoke and ash billows from a volcano in Eyjafjallajokull, Iceland Photograph: Ingolfur Juliusson/Reuters”
The Guardian caption is for the most part incorrect. Note that the volcanic cloud is largely indistinguishable from the other clouds, except for it’s shape. The reason for the similarity is that the vast majority of the volcanic plume is water vapour, not ash and definitely not smoke. Where would smoke come from??? There aren’t any trees on Iceland to burn.
The abundance of gases varies considerably from volcano to volcano. However, water vapor is consistently the most common volcanic gas, normally comprising more than 60% of total emissions. Carbon dioxide typically accounts for 10 to 40% of emissions.
70% of the earth’s surface is covered with water. Where did that water come from? It is generally believed that most of it outgased from the interior of the earth during the first 700 million years of the earth’s existence.
Steam from the interiorToday most authors believe that early steam from the hot mantle but already cool atmosphere, caused the oceans in the very early stages of the planet. They reason from studies of chondrites (space rocks) in space that under compression, enough water could be released to form an ocean. Today one can observe the gases escaping from active volcanoes, and these too contain water. In this scenario, the oceans would still be increasing in size, a gradual process that would never really end.The amount of water stored in rocks of the primary lithosphere is estimated at 25E21kg (Hutchinson G E, 1957), whereas the water in all oceans is 1.35E21kg, so it is quite possible that all this water emerged slowly after rocks were compressed and heated while the atmosphere had cooled already.
We know that the oceans could not have condensed out of the early atmosphere, because even a 100% water vapour atmosphere would only contain 10 metres of liquid water. People have hypothesized that the oceans came from comets, but the hydrogen isotope ratios in the oceans are different than that seen in comets Halley, Hyakutake and Hale-Bopp.
The only plausible origin of the oceans is from the interior of the earth. So why don’t we see oceans on other planets and the moon? Liquid water only exists in a narrow range of temperatures and pressures. Other planets are too hot, too cold or too small to hold liquid water, though some of the moons of the giant planets may have liquid water.
Why is the relationship between volcanoes and water important? Because steam pressure is the primary driver of explosive volcanic eruptions.
Below are some images of potentially explosive eruptions :
Mt. St. Helens 1980 : Mostly steam, some ash, almost no smoke.
The video above shows the moment of the big eruption May 18, 1980
Mayon 1984 USGS photo : Steam rising, ash cloud falling down the sides of the mountain.
Fourpeaked Volcano, Alaska 2006 USGS photo : 100% steam
Tungurahua 2006 NASA EO image : Steam, ash and lava
Eyjafjallajökull 2010 NASA EO image : Steam, lava, ice
Below are USGS images of non-explosive eruptions at Mauna Loa, Hawaii
Note in the image above that there is some smoke on the left side – from burning trees, and a little steam at the summit. So what is the difference between explosive and non-explosive eruptions? The difference is mainly due to the presence or absence of water. Water mainly enters volcanoes from two primary sources.
- Subduction on the sea floor, and transport upwards into a magma chamber. (Mt. St. Helens)
- Melt from snow and ice above. (Eyjafjallajökull and Mt. St. Helens)
Mauna Loa on the other hand has very little water mixed in with the magma, as it is neither near a subduction zone nor is it covered with snow most of the time. So eruptions from Mauna Loa tend to produce lava rather than steam and ash.
Looking at the mechanics, it becomes clear that explosive volcanic eruptions can not occur in the absence of large amounts of steam. Liquids (like magma) have very low compressibility and can not store enough mechanical energy to cause an explosion. Gases on the other hand are extremely compressible and can store vast amounts of energy. Steam has the unique property that it is liquid until it comes in contact with the magma (or the overburden pressure becomes low enough to allow it to switch to vapour phase) – then it converts thermal energy into mechanical energy very efficiently. The world used to run off steam engines based on this principle.
Most modern power plants still use steam to convert thermal energy into mechanical energy. Same principle that makes volcanoes explode.
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People who doubt that water is the cause of explosive volcanic eruptions should ask themselves “what is it that causes explosions?”
The main types of explosions are
1. Explosions caused by release of energy from chemical reactions. Not much of that going on in volcanoes.
2. Explosions caused by release of energy from nuclear reactions. Not much of that going on in volcanoes.
3. Explosions caused by conversion of thermal energy to mechanical energy, normally using steam as the transfer agent. Happens often in volcanoes.
4. Explosions caused by compressed gases (like water vapor) being released. Happens when dissolved gases in magma reach the surface.
All of the previous eruptions were precursors to more massive activity from the neighbouring Katla volcano, which this time, according to geologists, could take one to two years to erupt. And Eyjafjallajökull is the dwarf, Katla the giant.
http://english.pravda.ru/world/europe/17-04-2010/113070-iceland_volcano-0
Hoorah! Mechanical engineering comes to the rescue with a simple explanation on volcanic eruptions!
And for all the techno-geeks out there, remember this: with the exception of the miniscule contribution of wind, solar, biomass, etc., all significant electric generation, whether nuclear or fossil, starts out as steam driving a turbine which is coupled to a generator. The only difference is: nuclear derived steam is for the most part saturated; fossil derived steam is invariably superheated, more efficient and packs more of a punch per pound.
Increasing activity at the Katla volcano, live data:
http://hraun.vedur.is/ja/Katla2009/stodvaplott.html
“DirkH (13:02:22) :
[…]
of life can always continue – albeit on a nearly depleted atmospheric level of CO2 – always just short of starvation if you will…”
One more thought on this:
When CO2 depletion sets in, we will see plant die-back. Where will we see it? In the places where it’s hard for plants to survive, so deserts start to grow in the +-30 degree latitude range because of the Hadley cells. The available carbon doesn’t suffice to cover the entire available landmass area with plants, so some places turn into deserts.
So the Sahara and all the other great deserts are caused by a combination of CO2 and H2O scarcity.
stevengoddard (12:05:04) :
Mt. St. Helens is made up of layers of andesite and basalt, yet it is known to have rather explosive eruptions from time to time.
All the Plinian eruptions (explosive) are dacitic magmas (see 3rd link below). Dacite has the same relative percentage of silica that rhyolite does but tends to contain more calcium-rich feldspar (plagioclase versus potassium feldspars).
http://en.wikipedia.org/wiki/File:Dacite-AphaniticQAPF.gif
http://www.geology.sdsu.edu/how_volcanoes_work/Controls.html
http://geology.geoscienceworld.org/cgi/content/abstract/23/6/523
The largest explosive volcanoes, like Long Valley, Valles, and Yellowstone do contain Rhyolites. The reason that they store so much energy is because they are low temperature (viscous) magmas with lots of volatiles that can’t easily escape.
Again, the reason why the volatiles can’t escape is because of the high silica content. High silica means sticky lava/magma. Low silica means fluid lava/magma (hence, the volatiles escape early on before the magma gets any way near the surface).
The ash from the Icelandic volcano is andesitic in composition and is not normally erupt in a Plinian style.
stevengoddard (13:39:30) :
People who doubt that water is the cause of explosive volcanic eruptions should ask themselves “what is it that causes explosions?”
The main types of explosions are
1. Explosions caused by release of energy from chemical reactions. Not much of that going on in volcanoes.
2. Explosions caused by release of energy from nuclear reactions. Not much of that going on in volcanoes.
3. Explosions caused by conversion of thermal energy to mechanical energy, normally using steam as the transfer agent. Happens often in volcanoes.
4. Explosions caused by compressed gases (like water vapor) being released. Happens when dissolved gases in magma reach the surface.
I agree.
Wasn’t Spock a Vulcanologist?
For anybody doubting Steve, check this out, it gets real interesting about 4 1/2 minutes in.
johnythelowery (05:41:03)
Well said. But I don’t see that the flood covering the highest mountain is an issue if it occurred at the start of the supercontinent breakup. The highest mountains we know today (on earth) are caused by the tectonic plates colliding. So if the flood heralded the start of the breakup (hot water under pressure coming up from deep fissures – ‘the fountains of the deep’) – then present day highest mountains obviously couldn’t have formed yet. If it’s given that the supercontinent was flatter than our present day land masses, then covering the super continent in water doesn’t take as much water as one might initially surmise, as the highest mountain back then may have been like a hill in comparison.
Joe (05:01:11) :
I wonder if earth’s unexplained increases in orbit (somewhere around 10m/cy) could also be contributing to volcanic activity. I was hoping it might provide a mechanism for the expanding earth theory, but I may be hoping for too much there.
Matt B (18:29:40) :
Thank you. It’s a tough one really, frankly, the Noah story. Mt. Ararat and all that. I’m definately not a young earth guy but better get off this. Another time maybe.
Paul Hildebrandt (15:13:20) :
You said “High silica means sticky lava/magma. Low silica means fluid lava/magma (hence, the volatiles escape early on before the magma gets any way near the surface).”
This is true, but the reason why high silica magmas are viscous is because they melt at lower temperatures, and because they contain a lot of volatiles. It is the volatile gases which create the explosions, not the quartz/potassium feldspar content.
RE: johnythelowery (05:50:15) : “Maybe nitpicking, but let’s remember: clouds don’t consist of water vapour. It is water. Aerosol”
This is primarily why I do not like the term ‘water vapor.’ In common parlance, a ‘vapor’ is an aerosol. In most cases here, especially with regard to greenhouse (earthshine resonant) gases, the term ‘water vapor’ is used to indicate ‘clear air water content.’ I am not sure that this distinction is well understood by the general public.
Steve Schaper (23:52:26) :
“evening and morning”
again, translation problem
it does not say “night and day”
“evening and morning”, same as “ending and beginning”, or “dusking and dawning”, i.e., ending, dusking of one eon or era, beginning, dawning of a new one
Darkinbad the Brightdayler (00:19:01) :
A couple of glasses of Brennevin (Black Death) and all will become clear in the following joke from an Icelandic friend:
The economy has died, been cremated and its ashes are being scattered all over Europe.
…………………………………………………………………………………………………………..
Europe, from whence its economic problems came. But then Icelandic banks shouldn’t have been greedy and made themselves an offshore haven for European money.
KeithGuy (02:15:53) :
I heard an interesting take on the disruption of the Icelandic volcano on BBC radio today. It said:
“Good news for the carbon budget with all of those grounded planes.”
Eh?
I wonder what they think comes out of volcanoes?
………………………………………………………………………………………………………………
Ya, boy, they’re thinking.
Ian L. McQueen (12:18:46) :
On the water hypothesis, I question the recent posting that “This eruption is explosive (in regards to ash production) because the andesitic magma is coming in contact with the glacial meltwater and pulverizing the resulting cooling magma into very tiny particles of volcanic glass called ash.” My feeling is that the presence of ice / water outside the volcano is incidental and that the explosive nature is due only to the pressure of water and gases inside the magma.
What makes you think that the andesitic magma has enough water and other gases in it to cause a Plinian eruption?
A small quibble here, but according to Webster’s one definition of smoke is:
A suspension of particles in a gas
By this definition, the caption describing the cloud as smoke and ash is absolutely correct. Sure, we most often think of smoke as a combustion phenomena, but that’s not necessarily the only definition, just as we usually consider ash to be the carbonized remains of combustion, but of course volcanic ash is something else entirely.
Finally, pretty much all smoke, whether from combustion or otherwise consists largely of water vapour (in this case by vapour, I mean the mixture of steam and liquid aerosol particulates).
stevengoddard (19:40:58) :
This is true, but the reason why high silica magmas are viscous is because they melt at lower temperatures, and because they contain a lot of volatiles. It is the volatile gases which create the explosions, not the quartz/potassium feldspar content.
Ok, I’ll give you partial credit. However, please read the following (which is what I have been trying to impress upon you from the beginning):
Viscosity of Magmas
Viscosity is the resistance to flow (opposite of fluidity). Viscosity depends on primarily on the composition of the magma, and temperature.
* Higher SiO2 (silica) content magmas have higher viscosity than lower SiO2 content magmas (viscosity increases with increasing SiO2 concentration in the magma).
* Lower temperature magmas have higher viscosity than higher temperature magmas (viscosity decreases with increasing temperature of the magma). (I’ll give you partial credit here.)
Thus, basaltic magmas tend to be fairly fluid (low viscosity), but their viscosity is still 10,000 to 100,0000 times more viscous than water. Rhyolitic magmas tend to have even higher viscosity, ranging between 1 million and 100 million times more viscous than water. (Note that solids, even though they appear solid have a viscosity, but it very high, measured as trillions time the viscosity of water). Viscosity is an important property in determining the eruptive behavior of magmas.
Volcanic Eruptions
* In general, magmas that are generated deep within the Earth begin to rise because they are less dense than the surrounding solid rocks.
*
As they rise they may encounter a depth or pressure where the dissolved gas no longer can be held in solution in the magma, and the gas begins to form a separate phase (i.e. it makes bubbles just like in a bottle of carbonated beverage when the pressure is reduced).
*
When a gas bubble forms, it will also continue to grow in size as pressure is reduced and more of the gas comes out of solution. In other words, the gas bubbles begin to expand.
*
If the liquid part of the magma has a low viscosity, then the gas can expand relatively easily. When the magma reaches the Earth’s surface, the gas bubble will simply burst, the gas will easily expand to atmospheric pressure, and a non-explosive eruption will occur, usually as a lava flow (Lava is the name we give to a magma when it on the surface of the Earth).
*
If the liquid part of the magma has a high viscosity, then the gas will not be able to expand very easily, and thus, pressure will build up inside of the gas bubble(s). When this magma reaches the surface, the gas bubbles will have a high pressure inside, which will cause them to burst explosively on reaching atmospheric pressure. This will cause an explosive volcanic eruption.
Anyway, hit the wrong button. Wasn’t quite finished.
Gas does play a minor part in the viscosity of the magma. Let me repeat that, MINOR. Silica content is the main player. Here is the link to the article: Actually, it’s Geology 204 at Tulane.
http://www.tulane.edu/~sanelson/geol204/volcan&magma.htm
Here’s a better description from another source:
http://www.geology.sdsu.edu/how_volcanoes_work/Controls.html
MAGMA VISCOSITY, TEMPERATURE, AND GAS CONTENT
The viscosity of a substance is a measure of its consistency. Viscosity is defined as the ability of a substance to resist flow. In a sense, viscosity is the inverse of fluidity. Cold molasses, for example, has a higher viscosity than water because it is less fluid. A magma’s viscosity is largely controlled by its temperature, composition, and gas content. The effect of temperature on viscosity is intuitive. Like most liquids, the higher the temperature, the more fluid a substance becomes, thus lowering its viscosity.
Composition plays an even greater role in determining a magma’s viscosity. A magma’s resistance to flow is a function of its “internal friction” derived from the generation of chemical bonds within the liquid. Chemical bonds are created between negatively charged and positively charged ions (anions and cations, respectively). Of the ten most abundant elements found in magmas (see above), oxygen is the only anion. Silicon, on the other hand, is the most abundant cation. Thus, the Si-O bond is the single most important factor in determining the degree of a magma’s viscosity. These two elements bond together to form “floating radicals” in the magma, while it is still in its liquid state (i.e., Si-O bonds begin to form well above the crystallization temperature of magma). These floating radicals contain a small silicon atom surrounded by four larger oxygen atoms (SiO4). This atomic configuration is in the shape of a tetrahedron. The radicals are therefore called silicon-oxygen tetrahedra, as shown here.
These floating tetrahedra are electrically charged compounds. As such, they they are electrically attracted to other Si-O tetrahedra. The outer oxygen atoms in each tetrahedron can share electrons with the outer oxygen atoms of other tetrahedra. The sharing of electrons in this manner results in the development of covalent bonds between tetrahedra. In this way Si-O tetrahedra can link together to form a variety shapes: double tetrahedra (shown here, C), chains of tetrahedra, double chains of tetrahedra, and complicated networks of tetrahedra. As the magma cools, more and more bonds are created, which eventually leads to the development of crystals within the liquid medium. Thus, the Si-O tetrahedra form the building blocks to the common silicate minerals found in all igneous rocks. However, while still in the liquid state, the bonding of tetrahedra results in the polymerization of the liquid, which increases the “internal friction” of the magma, so that it more readily resists flow. Magmas that have a high silica content will therefore exhibit greater degrees of polymerization, and have higher viscosities, than those with low-silica contents.
The amount of dissolved gases in the magma can also affect it’s viscosity, but in a more ambiguous way than temperature and silica content. When gases begin to escape (exsolve) from the magma, the effect of gas bubbles on the bulk viscosity is variable. Although the growing gas bubbles will exhibit low viscosity, the viscosity of the residual liquid will increase as gas escapes. The overall bulk viscosity of the bubble-liquid mixture depends on both the size and distribution of the bubbles. Although gas bubbles do have an effect on the viscosity, the more important role of these exsolving volatiles is that they provide the driving force for the eruption.
Hopefully, this will help clear thing up for you.
There are some VERY cool photos of volcanic lightning posted on this site, check ’em out!
http://www.spaceweather.com/
Oh yeah, “the sun is blank, no sunspots.”
Hot off the press – Quake hits Kalgoorlie, Western Australia
The quake struck with a magnitude of 4.8 at 8.17am (WST) on Tuesday, Geoscience Australia said.
This is the largest event in the last 25 years in this region and it might be the largest since we started recording
From http://au.news.yahoo.com/a/-/latest/7084400/quake-hits-kalgoorlie-damages-buildings/
Paul Hildebrandt (20:13:17) : [Surface Water Driven Volcanic Explosions]
My take on this is that a truly explosive eruption requires confinement of the water in contact with magma so that pressure can build up to the surface-rupture point. If you have a mechanism that allows surface water to leak into the magma stream and subsequently be confined long enough to allow explosively high pressures to develop then I would agree that this is possible. I note that the undersea volcanoes near Hawaii have not produced any grand explosive eruptions.
I suspect that water entrained in marine rocks subducted from the sea floor might produce a much more explosive emerging magma than similar material subducted from a dry environment.
The late Professor Lance Endersbee, Emeritus Professor; former Dean of Engineering and Pro-Vice Chancellor of Monash University claimed that water was created internally.
Endersbee’s main focus was on the state of the world’s groundwater, the rapid consumption of which has put the world on the edge of a little understood catastrophe because contrary to popular belief groundwater reserves are not replenished from the surface.
http://www.abc.net.au/rn/latenightlive/stories/2006/1808528.htm
http://mpegmedia.abc.net.au/rn/podcast/2006/12/lnl_20061211.mp3
Spector (21:42:48) :
If you put a bullet in a fire, it will make a loud bang. If you put a bullet in a gun in a fire, it can be lethal. The explosion which sends the bullet flying at high speed is created by the confinement inside the steel barrel and chamber of the gun.
Don’t try either experiment at home.
BTW – if you took a .223 rifle to the moon and pointed it straight up in the “air,” the bullet would travel well over 50 miles upwards before it started to fall.