P'u'u O'o Crater, Hawai'i, 2005

Video Credits: Th. Böckel

Puʻu ʻŌʻō (often written Puu Oo) is a volcanic cone in the eastern rift zone of the Kīlauea volcano of the Hawaiian Islands. Puʻu ʻŌʻō has been erupting continuously since January 3, 1983, making it the longest-lived rift-zone eruption of the last two centuries.

By January 2005, 2.7 cubic kilometers (0.65 cu mi) of magma covered an area of more than 117 square kilometers (45 sq mi) and added 230 acres (0.93 km2) of land to the Southeast coast of Hawaiʻi. So far, the eruption has claimed 189 buildings and 14 kilometres (8.7 mi) of highways, as well as a church, a store, the Wahaʻula Visitor Centre, and many ancient Hawaiian sites, including the Wahaʻula heiau. The coastal highway has been closed since 1987, as it has been buried under lava up to 35 meters (115 ft) thick.

Volcanism and Igneous Rocks

Magma and Igneous Rocks Igneous Rocks are  formed by crystallization from a liquid, or magma. They include two types Volcanic or extrusive  igneous rocks form when the magma cools and crystallizes on the surface of the Earth Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the Earth. Magma is a mixture of liquid rock, crystals, and gas. Characterized by a wide range of chemical compositions, with high temperature, and  properties of a liquid. Magmas are less dense than surrounding rocks, and will therefore move upward. If magma makes it to the surface it will erupt and later crystallize to form an extrusive or volcanic rock. If it crystallizes before it reaches the surface it will form an igneous rock at depth called aplutonic or intrusive igneous rock.

Types of Magma Chemical composition of magma is controlled by the abundance of elements in the Earth. Si, Al, Fe, Ca, Mg, K, Na, H, and O make up 99.9%. Since oxygen is so abundant, chemical analyses are usually given in terms of oxides. SiO2 is the most abundant oxide. Mafic or Basaltic--  SiO2 45-55 wt%, high in Fe, Mg, Ca, low in K, Na  Intermediate or Andesitic--  SiO2 55-65 wt%, intermediate. in Fe, Mg, Ca, Na, K  Felsic or Rhyolitic--  SiO2 65-75%, low in Fe, Mg, Ca, high in K, Na. Gases - At depth in the Earth nearly all magmas contain gas.  Gas gives magmas their explosive character, because the gas expands as pressure is reduced. Mostly H2O with some CO2  Minor amounts of Sulfur, Cl , and F  Felsic magmas usually have higher gas contents than mafic magmas. Temperature of Magmas Mafic/Basaltic - 1000-1200oC  Intermediate/Andesitic -  800-1000oC  Felsic/Rhyolitic -  650-800oC. Viscosity of Magmas Viscosity is the resistance to flow (opposite of fluidity). Depends on composition, temperature, & gas content.   Higher SiO2 content magmas have higher viscosity than lower SiO2 content magmas  Lower Temperature magmas have higher viscosity than higher temperature magmas.

Summary Table
Magma Type	Solidified Volcanic Rock	Solidified Plutonic Rock	Chemical Composition	Temperature	Viscosity	Gas Content
Mafic or Basaltic	Basalt	Gabbro	45-55 SiO2 %, high in Fe, Mg, Ca, low in K, Na	1000 - 1200 oC	Low	Low
Intermediate or Andesitic	Andesite	Diorite	55-65 SiO2 %, intermediate in Fe, Mg, Ca, Na, K	800 - 1000 oC	Intermediate	Intermediate
Felsic or Rhyolitic	Rhyolite	Granite	65-75 SiO2 %, low in Fe, Mg, Ca, high in K, Na	650 - 800 oC	High	High

Origin of Magma As we have seen the only part of the earth that is liquid is the outer core.  But the core is not likely to be the source of magmas because it does not have the right chemical composition.  The outer core is mostly Iron, but magmas are silicate liquids.  Thus magmas DO NOT COME FROM THE MOLTEN OUTER CORE OF THE EARTH.  Thus, since the rest of the earth is solid, in order for magmas to form, some part of the earth must get hot enough to melt the rocks present. We know that temperature increases with depth in the earth along thegeothermal gradient.  The earth is hot inside due to heat left over from the original accretion process, due to heat released by sinking of materials to form the core, and due to heat released by the decay of radioactive elements in the earth.  Under normal conditions, the geothermal gradient is not high enough to melt rocks, and thus with the exception of the outer core, most of the Earth is solid.  Thus, magmas form only under special circumstances.  To understand this we must first look at how rocks and mineral melt. As pressure increases in the Earth, the melting temperature changes as well.  For pure minerals, there are two general cases.

For a pure dry (no H2O or CO2present) mineral, the melting temperate increases with increasing pressure.

For a mineral with H2O or CO2present, the  melting temperature first decreases with increasing pressure

Since rocks mixtures of minerals, they behave somewhat differently.  Unlike minerals, rocks do not melt at a single temperature, but instead melt over a range of temperatures.  Thus, it is possible to have partial melts from which the liquid portion might be extracted to form magma.  The two general cases are:

Melting of dry rocks is similar to melting of dry minerals, melting temperatures increase with increasing pressure, except there is a range of temperature over which there exists a partial melt.  The degree of partial melting can range from 0 to 100%

Melting of rocks containing water or carbon dioxide is similar to melting of wet minerals, melting temperatures initially decrease with increasing pressure, except there is a range of temperature over which there exists a partial melt.

Three ways to Generate MagmasFrom the above we can conclude that in order to generate a magma in the solid part of the earth either the geothermal gradient must be raised in some way or the melting temperature of the rocks must be lowered in some way. The geothermal gradient can be raised by upwelling of hot material from below either by uprise solid material (decompression melting) or by intrusion of magma (heat transfer). Lowering the melting temperature can be achieved by adding water or Carbon Dioxide (flux melting).

Decompression Melting  - Under normal conditions the temperature in the Earth, shown by the geothermal gradient, is lower than the beginning of melting of the mantle.  Thus in order for the mantle to melt there has to be a mechanism to raise the geothermal gradient.  Once such mechanism is convection, wherein hot mantle material rises to lower pressure or depth, carrying its heat with it.

If the raised geothermal gradient becomes higher than the initial melting temperature at any pressure, then a partial melt will form.  Liquid from this partial melt can be separated from the remaining crystals because, in general, liquids have a lower density than solids.  Basaltic magmas appear to originate in this way. Upwelling mantle appears to occur beneath oceanic ridges, at hot spots, and beneath continental rift valleys.  Thus, generation of magma in these three environments is likely caused by decompression melting.

Transfer of Heat-  When magmas that were generated by some other mechanism intrude into cold crust, they bring with them heat.  Upon solidification they lose this heat and transfer it to the surrounding crust.   Repeated intrusions can transfer enough heat to increase the local geothermal gradient and cause melting of the surrounding rock to generate new magmas.

Transfer of heat by this mechanism may be responsible for generating some magmas in continental rift valleys, hot spots, and subduction related environments. Flux Melting - As we saw above, if water or carbon dioxide are added to rock, the melting temperature is lowered.   If the addition of water or carbon dioxide takes place deep in the earth where the temperature is already high, the lowering of melting temperature could cause the rock to partially melt to generate magma.  One place where water could be introduced is at subduction zones. Here, water present in the pore spaces of the subducting sea floor or water present in minerals like hornblende, biotite, or clay minerals would be released by the rising temperature and then move in to the overlying mantle.   Introduction of this water in the mantle would then lower the melting temperature of the mantle to generate partial melts, which could then separate from the solid mantle and rise toward the surface.

Chemical Variability of Magmas The chemical composition of magma can vary depending on the rock that initially melts (the source rock), and process that occur during partial melting and transport. Initial Composition of Magma The initial composition of the magma is dictated by the composition of the source rock and the degree of partial melting.   In general, melting of a mantle source (garnet peridotite) results in mafic/basaltic magmas.  Melting of crustal sources yields more siliceous magmas. In general more siliceous magmas form by low degrees of partial melting. As the degree of partial melting increases, less siliceous compositions can be generated. So, melting a mafic source thus yields a felsic or intermediate magma. Melting of ultramafic (peridotite source) yields a basaltic magma. Magmatic Differentiation But, processes that operate during transportation toward the surface or during storage in the crust can alter the chemical composition of the magma.   These processes are referred to asmagmatic differentiation and include assimilation, mixing, and fractional crystallization. Assimilation - As magma passes through cooler rock on its way to the surface it may partially melt the surrounding rock and incorporate this melt into the magma. Because small amounts of partial melting result in siliceous liquid compositions, addition of this melt to the magma will make it more siliceous. Mixing - If two magmas with different compositions happen to come in contact with one another, they could mix together. The mixed magma will have a composition somewhere between that of the original two magma compositions. Evidence for mixing is often preserved in the resulting rocks. Fractional Crystallization - When magma crystallizes it does so over a range of temperature. Each mineral begins to crystallize at a different temperature, and if these minerals are somehow removed from the liquid, the liquid composition will change. The processes is called magmatic differentiation by Fractional Crystallization. Because mafic minerals like olivine and pyroxene crystallize first, the process results in removing Mg, Fe, and Ca, and enriching the liquid in silica. Thus crystal fractionation can change a mafic magma into a felsic magma. Crystals can be removed by a variety of processes. If the crystals are more dense than the liquid, they may sink. If they are less dense than the liquid they will float. If liquid is squeezed out by pressure, then crystals will be left behind. Removal of crystals can thus change the composition of the liquid portion of the magma. Let me illustrate this using a very simple case. Imagine a liquid containing 5 molecules of MgO and 5 molecules of SiO2. Initially the composition of this magma is expressed as 50% SiO2 and 50% MgO. i.e. Now let's imagine I remove 1 MgO molecule by putting it into a crystal and removing the crystal from the magma. Now what are the percentages of each molecule in the liquid?   If we continue the process one more time by removing one more MgO molecule Thus, composition of liquid can be changed.

Bowen's Reaction Series Bowen found by experiment that the order in which minerals crystallize from a basaltic magma depends on temperature.  As a basaltic magma is cooled Olivine and Ca-rich plagioclase crystallize first.  Upon further cooling, Olivine reacts with the liquid to produce pyroxene and Ca-rich plagioclase react with the liquid to produce less Ca-rich plagioclase.  But, if the olivine and Ca-rich plagioclase are removed from the liquid by crystal fractionation, then the remaining liquid will be more SiO2 rich.  If the process continues, an original basaltic magma can change to first an andesite magma then a rhyolite magma with falling temperature

Igneous Environments and Igneous Rocks The environment in which magma completely solidifies to form a rock determines: The type of rock The appearance of the rock as seen in its texture The type of rock body. In general there are two environments to consider: The intrusive or plutonic environment is below the surface of the earth. This environment is characterized by higher temperatures which result in slow cooling of the magma.  Intrusive or plutonic igneous rocks form here. Where magma erupts on the surface of the earth, temperatures are lower and cooling of the magma takes place much more rapidly.  This is the extrusive or volcanic environment and results in extrusive or volcanic igneous rocks. Extrusive Environments When magmas reach the surface of the Earth they erupt from a vent called a volcano.  They may erupt explosively or non-explosively. Non-explosive eruptions are favored by low gas content and low viscosity magmas (basaltic to andesitic magmas and sometimes rhyolitic magma). Usually begin with fire fountains due to release of dissolved gases Produce lava flows on surface Produce Pillow lavas if erupted beneath water

Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic magmas). Expansion of gas bubbles is resisted by high viscosity of magma - results in building of pressure High pressure in gas bubbles causes the bubbles to burst when reaching the low pressure at the Earth's surface. Bursting of bubbles fragments the magma into pyroclasts and tephra (ash). Cloud of gas and tephra rises above volcano to produce an eruption column that can rise up to 45 km into the atmosphere.

Tephra that falls from the eruption column produces a tephra fall deposit.

If eruption column collapses a pyroclastic flow may occur, wherein gas and tephra rush down the flanks of the volcano at high speed.  This is the most dangerous type of volcanic eruption.  The deposits that are produced are called ignimbrites.

Intrusive Environments Magma that cools at depth form bodies of rocks called intrusive bodies or plutonic bodies called plutons, from Greek god of the underworld - Pluto. When magma intrudes it usually affects the surrounding rock and is also affected by the surrounding rock.  It may metamorphose the surrounding rocks or cause hydrothermal alteration. The magma itself may also cool rapidly near the contact with the surrounding rock and thus show a chilled margin next to the contact.

It may also incorporate pieces of the surrounding rocks without melting them.  These incorporated pieces are called xenoliths (foreign rocks). Magma intrudes by injection into fractures in the rock and expanding the fractures.   The may also move by a process called stoping, wherein bocks are loosened by magma at the top of the magma body with these blocks then sinking through the magma to accumulate on the floor of the magma body.

In relatively shallow environments intrusions are usually tabular bodies like dikes and sills or domed roof bodies called laccoliths.
Dikes are small (<20 m wide) shallow intrusions that show a discordant relationship to the rocks in which they intrude.  Discordant means that they cut across preexisting structures.  They may occur as isolated bodies or may occur as swarms of dikes emanating from a large intrusive body at depth.
Sills are also small (<50 m thick) shallow intrusions that show a concordant relationship with the rocks that they intrude.  Sills usually are fed by dikes, but these may not be exposed in the field.
Laccoliths are somewhat large intrusions that result in uplift and folding of the preexisting rocks above the intrusion.  They are also concordant types of intrusions.

Deeper in the earth intrusion of magma can form bulbous bodies called plutons and the coalescence of many plutons can form much larger bodies called batholiths. Plutons are large intrusive bodies, of any shape that intrude in replace rocks in an irregular fashion.  Stocks are smaller bodies that are likely fed from deeper level batholiths.  Stocks may have been feeders for volcanic eruptions, but because large amounts of erosion are required to expose a stock or batholith, the associated volcanic rocks are rarely exposed.

If multiple intrusive events occur in the same part of the crust, the body that forms is called abatholith.  Several large batholiths occur in the western U.S. - The Sierra Nevada Batholith, the Coast Range Batholith, and the Idaho Batholith, for example (See figure 6.10d in your text).

During a magmatic event there is usually a close relationship between intrusive activity and extrusive activity, but one cannot directly observe the intrusive activity.   Only after erosion of the extrusive rocks and other rock above the intrusions has exposed the intrusions do they become visible at the earth's surface (see figure 6.10a in your text).

The rate of cooling of magma depends largely on the environment in which the magma cools.   Rapid cooling takes place on the Earth's surface where there is a large temperature contrast between the atmosphere/ground surface and the magma.  Cooling time for material erupted into air and water can be as short as several seconds.   For lava flows cooling times are on the order of days to weeks.   Shallow intrusions cool in months to years and large deep intrusions may take millions of years to cool.

Because cooling of the magma takes place at a different rate, the crystals that form and their interrelationship (texture) exhibit different properties. Fast cooling on the surface results in many small crystals or quenching to a glass. Gives rise to aphanitic texture (crystals cannot be distinguished with the naked eye), or obsidian (volcanic glass).

Slow cooling at depth in the earth results in fewer much larger crystals, gives rise to phaneritic texture.

Porphyritic texture develops when slow cooling is followed by rapid cooling. Phenocrysts = larger crystals, matrix orgroundmass = smaller crystals.

Classification of Igneous Rocks  Igneous rocks are classified on the basis of texture and chemical composition, usually as reflected in the minerals that from due to crystallization.   You will explore the classification of igneous rocks in the laboratory portion of this course.

Extrusive/Volcanic Rocks Basalts, Andesites, and Rhyolites are all types of volcanic rock distinguished on the basis of their mineral assemblage and chemical compostion (see figure 6.13 in your text).  These rocks tend to be fine grained to glassy or porphyritic.  Depending on conditions present during eruption and cooling, any of these rock types may form one of the following types of volcanic rocks. Obsidian - dark colored volcanic glass showing concoidal fracture and few to no crystals. Usually rhyolitic . Pumice - light colored and light weight rock consisting of mostly holes (vesicles) that were once occupied by gas, Usually rhyolitic or andesitic. Vesicular rock - rock filled with holes (like Swiss cheese) or vesicles that were once occupied by gas. Usually basaltic and andesitic. If vesicles in a vesicular basalt are later filled by precipitation of calcite or quartz, the fillings are termed amygdules and the basalt is termed an amygdularl basalt.

Pyroclasts = hot, broken fragments. Result from explosively ripping apart of magma. Loose assemblages of pyroclasts called tephra. Depending on size, tephra can be classified as bombs. lapilli, or ash. Rock formed by accumulation and cementation of tephra called a pyroclastic rock or tuff. Welding, compactioncause tephra (loose material) to be converted in pyroclastic rock.

Intrusive/Plutonic Igneous Rocks Shallow intrusions like dikes and sills are usually fine grained and sometimes porphritic because cooling rates are similar to those of extrusive rocks.   Classification is similar to the classification for volcanic/extrusive rocks.  Coarse grained rocks, formed at deeper levels in the earth include gabbros, diorites, and granites.  Note that these are chemically equivalent to basalts, andesites, and rhyolites, but may have different minerals or different proportions of mineral because their crystallization history is not interrupted as it might be for extrusive rocks (see figure 6.13 in your text). Pegmatites are very coarse grained igneous rocks consisting mostly of quartz and feldspar as well as some more exotic minerals like tourmaline, lepidolite, muscovite.  These usually form dikes related to granitic plutons. Distribution of Igneous Activity Igneous activity is currently taking place as it has in the past in various tectonic settings.   These include diverging and converging plate boundaries, hot spots, and rift valleys. Divergent Plate Boundaries At oceanic ridges, igneous activity involves eruption of basaltic lava flows that form pillow lavas at the oceanic ridges and intrusion of dikes and plutons beneath the ridges.   The lava flows and dikes are basaltic and the plutons mainly gabbros.   These processes form the bulk of the oceanic crust as a result of sea floor spreading.  Magmas are generated by decompression melting as hot solid asthenosphere rises and partially melts. Convergent Plate Boundaries Subduction at convergent plate boundaries introduces water into the mantle above the subduction and causes flux melting of the mantle to produce basaltic magmas.  These rise toward the surface differentiating by assimilation and crystal fractionation to produce andesitic and rhyolitic magmas.  The magmas that reach the surface build island arcs and continental margin volcanic arcs built of basalt, andesite, and rhyolite lava flows and pyroclastic material.  The magmas that intrude beneath these arcs can cause crustal melting and form plutons and batholiths of diorite and granite Hot Spots As discussed previously, hot spots are places are places where hot mantle ascends toward the surface as plumes of hot rock.  Decompression melting in these rising plumes results in the production of magmas which erupt to form a volcano on the surface or sea floor, eventually building a volcanic island.  As the overriding plate moves over the hot spot, the volcano moves off of the hot spot and a new volcano forms over the hot spot.  This produces a hot spot track consisting of lines of extinct volcanoes leading to the active volcano at the hot spot.  A hot spot located beneath a continent can result in heat transfer melting of the continental crust to produce large rhyolitic volcanic centers and plutonic granitic plutons below.   A good example of a continental hot spot is at Yellowstone in the western U.S.  Occasionally a hot spot is coincident with an oceanic ridge.  In such a case, the hot spot produces larger volumes of magma than normally occur at ridge and thus build a volcanic island on the ridge.  Such is the case for Iceland which sits atop the Mid-Atlantic Ridge. Rift Valleys Rising mantle beneath a continent can result in extensional fractures in the continental crust to form a rift valley.  As the mantle rises it undergoes partial melting by decompression, resulting in the production of basaltic magmas which may erupt as flood basalts on the surface.   Melts that get trapped in the crust can release heat resulting in melting of the crust to form rhyolitic magmas that can also erupt at the surface in the rift valley.  An excellent example of a continental rift valley is the East African Rift.  Large Igneous Provinces In the past, large volumes of mostly basaltic magma have erupted on the sea floor to form large volcanic plateaus, such as the Ontong Java Plateau in the eastern Pacific.   Such large volume eruptions can have affects on the oceans because they change the shape of ocean floor and cause a rise in sea level, that sometimes floods the continents.   The plateaus form obstructions which can drastically change ocean currents. These changes in the ocean along with massive amounts of gas released by the magmas can alter climate and have drastic effects on life on the planet.

330 million years old volcano discovered near Mullingar, Co Westmeath

How Mullingar might look with a volcano nearby

Three hundred million year old volcanoes have been found under the midlands.

A low flying air ship utilizing the most recent mapping innovation has revealed the 330 million-year-old rock developments on the Westmeath/Offaly outskirt south of Mullingar.

It additionally indicated groups of volcanic rocks a few kilometers under the ground close Strokestown, Co Roscommon – some piece of a noteworthy deficiency line that can be followed through Ireland to Scotland.

The revelations were made in the most recent piece of the Government's Tellus program.

Flying at 90metres, air ship use innovation to see through Ireland's profound frigid stores and broad peat spread.

Specialists said the destinations will be of enthusiasm to organizations watchful for mineral stores.

Beam Scanlon, important geologist at the Geological Survey of Ireland, said: "Tellus keeps on uncovering unprecedented new detail in Ireland's geographical scene covered underneath our feet, expanding after existing information holes and creating regular asset opportunities.

"A comprehension of Ireland's topography is indispensable for natural, wellbeing and financial reasons and the information will be invited by a wide scope of partners for agrarian, radon aversion, groundwater security and mineral investigation purposes."

Tellus plans to finish a topographical jigsaw of the island of Ireland and wants to have a large portion of the nation secured before the end of 2017.

The Midlands discoveries are huge as they make up another bit of the jigsaw which started in 2007.

The fourth period of Tellus is in progress crosswise over eastern Ireland where the overview over Offaly, Kildare , Meath , Dublin and northern parts of Wicklow and Laois is just about 60 for every penny complete.

Right now the undertaking is centered around country district Dublin .

The uniquely prepared flying machine conveys three instruments on load up measuring attraction, conductivity and regular radiation of the stones and soils underneath.

Tellus is a piece of Ireland's earth science office, the Geological Survey of Ireland, established in 1845.

The overview is in charge of gathering land data and giving guidance and data including maps, reports and databases.

It is a Department's piece of Communications, Energy and Natural Resources and has around 50 staff.

Geology: Definitely NOT a Boring Science!!

I recently shifted my major in college to geoscience so that I could finally pursue a long-time, childhood interest of mine: paleontology. I love paleontology. I absolutely adore the idea of studying ancient creatures that are long-extinct, and yet are the precursors of life on Earth today. I think our knowledge of evolution is truthfully amazing, and the thought that there is a field of science that studies evolution in a broad context is awesome to me. Paleontology has strong (and obvious) ties to geology (because you have to dig the damned fossils out of the dirt to get to them), and so there is quite a lot to learn about the rocks you’ll be digging in before you can get to the “goods”, so to speak. What’s actually the most surprising is that there is a rather staggering amount one can learn from studying geology; there’s more to it than just rocks!

With that thought in mind, it always interested me that most people think of geology as being one of the more “boring” sciences. I really have no way of relating to the idea that any field of science is boring, and so this line of thought really intrigues me from a sort of interpersonal academic kind of direction. Whenever I hear the words “geology is boring” I am always the first to jump up and ask: “How could volcanoes, continental drift, catastrophic disasters and mountain building be boring? It’s awesome!” Usually when I say that sort of thing, the response of “well yeah, those things are cool, but geology itself is really boring” is usually what I get in return. I’m always a little dumbfounded by that response. In essence, all of those things are what make geology REALLY awesome and fun to study, making it worthy of serious research as one of the hard sciences, but people usually don’t think of those things when they think of geology, and there are a few reasons for that (that I will get to later). For this blog posting, I want to begin by covering what geology is and why it is an important science (also illustrating along the way why it is that geology is awesome), and then I want to wrap this up with my thoughts on why many people don’t share my enthusiasm for it.

 Do you know what this is? Do you know why it looks that way?

Understanding geological processes is interesting for many reasons. The academic interest of just wanting to know more about the world is one of the big attractions for many people to get into the field, as studying geology can give a researcher a lot of insight into the processes that have built the geography of the planet we live on in a very interesting deep time perspective. Geology gives a certain amount of deep context and meaning to things that we might just normally look at as, let’s say, interesting formations on a streambed, or something. Studying the rocks of the Earth might seem like a pretty basic and almost boring science, but it gives deep insight into things such as volcanism or erosion, forces that shape the world around us even today.
                     

On fire: Kawika Singson was shooting in the volcanoes of Hawaii, which was so hot his tripod and shoes caught alight

The science of geology also allows scientists to study more outwardly exciting topics such as volcanism, making those oh-so-awesome lava flows we see on National Geographic every now and again that much more exciting for a very simple reason: we can not only know, but inform people as to why that happens. It changed your perspective on your home planet when you realize that there are oceans of molten rock beneath your feet, heated by immense pressure, blasting through the surface from time to time. In understanding volcanism, one also begins to understand plate tectonics. Think about the idea of plate tectonics for a minute; the surface of the Earth being broken up into multiple gigantic plates of rock is still a new idea (comparatively speaking), and continental drift is fascinating in its own right. Just knowing a little about the theory of plate tectonics really takes your mind into a sort of psychological time-warp, because you suddenly realize that your world is dynamic, and has been changing for hundreds of millions, even BILLIONS of years. That kind of perspective on time is brought to you courtesy of your friendly neighborhood geologist.

Figuring out the ages of rocks also falls under the blanket of geological science. This is one of the places where geology crosses over into two other fields, these being physics and chemistry. To know the age of a rock, one needs to take a sample of the rock and vaporize it in a mass spectrometer so that one can read the spectral lines to determine its chemical content. The kind of understanding required to comprehend those lines of color (or lack thereof in terms of absorption lines) requires an understanding of physics with direct reference to atomic structure and electron orbitals; this also requires knowledge of chemistry to really grasp exactly what that sample was made of. The dating of rocks usually falls into one of two columns: absolute dating and relative dating. Absolute dating relies on the ratio of original to what are usually called “daughter” isotopes within a given sample of rock as unstable isotopes of many elements decay over time. The understanding of why those atoms decay the way they do requires another venture into physics to understand quantum tunneling and the Weak Nuclear Force, fields of research that are fascinating in their own right. Erosion, which is another phenomenon that geologists study, is often influenced not only by mechanical factors such as landslides, rushing rivers, etc. (which have gravity involved in their processes, which requires another aside into physics) but also by chemical factors, which requires a geologist to more fully delve into chemistry. In this way we can see geology as being a science that is fundamentally intertwined with other major sciences, creating a blend of knowledge that many might not imagine was originally there.

But physics and chemistry are not the only sciences contributing to greater geological knowledge; astronomy has something to say, as well. Some geological processes, like the erosion of a coastal cliff-face due to the pounding of the waves, have astronomical machinery at work. The tides are driven by the gravitational attraction of the Moon on the Earth’s oceans, causing large bodies of water to oscillate in tides that help shape and/or destroy different features on coastlines everywhere. The noticeable gravitational tug on our tiny world from both the Sun and Moon may also play a role in how tectonic plates move and help further shape the planet we live on. Many geologists also study climate, both ancient and modern, which requires at least some understanding of things like the solar wind, atmospheric chemical composition, etc. Though astronomy may seem far away from everyday geologic study, it sometimes stands at the forefront.

The study of geology also yields clues as to how and why certain organisms evolve the way they did. We have to keep in mind here that biological evolution is not only driven by things like predation and sex, but also by climate, weather, erosion, uplift, deposition, ocean currents (which can be changed due to the movement of tectonic plates) and many other factors that have their roots in geology. While the slow uplift of a mountain range might not seem like it would effect such a plastic and adaptable thing such as life, that mountain range may one day splinter a single population of organisms into two, three, or four different groups, giving evolution lots to work with and do its magic on. Paleontology, with these thoughts in mind, is sort of where geology and biology collide and create a science that is both and neither at the same time. In my own opinion, it is the interrelatedness of geology with all the other sciences that makes it so interesting and magnificent as its own study.

Geology also has a ton of subfields, such as:

• Earth science
• Economic geology
  • Mining geology
  • Petroleum geology
• Engineering geology
• Environmental geology
• Geoarchaeology
• Geochemistry
  • Biogeochemistry
  • Isotope geochemistry
• Geochronology
• Geodetics
• Geography
• Geological modelling
• Geometallurgy
• Geomicrobiology
• Geomorphology
• Geomythology
• Geophysics
• Glaciology
• Historical geology
• Hydrogeology
• Meteorology
• Mineralogy
• Oceanography
  • Marine geology
• Paleoclimatology
• Paleontology
  • Micropaleontology
  • Palynology
• Petrology
• Petrophysics
• Plate tectonics
• Sedimentology
• Seismology
• Soil science
  • Pedology (soil study)
• Speleology
• Stratigraphy
  • Biostratigraphy
  • Chronostratigraphy
  • Lithostratigraphy
• Structural geology
• Volcanology

So why don’t more people get really excited about geology shows on TV, geology lectures, or anything else related to such a fascinating science? I think the author of the “For Dummies” edition on Geology said it best. The author mentioned that rocks are everyday things, and so we don’t really think about them as being important, because they are essentially everywhere. A geologist might tell you something truly amazing, but because of that association with the mundane it might not be paid attention to, whereas an astronomer can say something relatively mundane about their own field and be thought of as sharing truthfully groundbreaking information simply because stars are far outside our everyday experience (other than twinkling in the night sky, that is). We associate geology with the mundane, and so, to us, it is immensely boring. I think we have also built a cultural picture of what a geologist is, as well. We picture geologists as boring, verbose little men that say a lot of big words, and to us that is unappealing. In a way, we’ve done that with all the sciences by constantly depicting scientists as often short-sighted and socially inept people wearing labcoats and stinking of Firefly fandom. In a way, interest in geology suffers from social conceptions of what geology is and what geologists are, but it also suffers because rocks are freakin’ everywhere, and looking at a rock is almost never fun.

 Sure isn’t boring to me.

Just a thought.

Lava flows in Pahoa

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Earth Story - Ring Of Fire

Fourth volcanic eruption this year for Piton de la Fournaise

The volcano on the Reunion island has erupted the fourth time this year which has attracted tourist.

How New Island forms?

A new island emerges off Japan coast after volcano eruption.

What is a Volcanic Hotspot?

The Most Incredible Volcano close view

Most Amazing Volcano Eruption Footage Shots!

Forecasting Volcanic Activity

A forecast for a volcanic eruption is a probabilistic statement concerning the time, place, and character of an eruption before it occurs. It is analogous to forecasting the weather and is not as precise a statement as a prediction. Forecasting volcanic eruptions is a major component of the goal to reduce volcanic hazards. It is unlikely that we will be able to forecast the majority of volcanic activity accurately in the near future, but valuable information is being gathered about phenomena that occur before eruptions. One problem is that most forecasting techniques require experience with actual eruptions before the mechanism is understood. Thus, we are better able to predict eruptions in the Hawaiian Islands then elsewhere because we have had so much experience there. 

The methods of forecasting volcanic eruptions include: 

• Monitoring of seismic activity.
• Monitoring of thermal, magnetic, and hydrologic conditions. 
• Topographic monitoring of tilting or swelling of the volcano. 
• Monitoring of volcanic gas emissions. 
• Studying the geologic history of a particular volcano or volcanic centre.

Seismic Activity 

A Volcano reawakens Increased seismic activity is a good indicator of a forthcoming volcanic eruption. As a dormant volcano reawakens, rising magma fractures rock above. At first, the fracturing slowly increases the rate of seismic activity; then, both the fracturing and seismic activity accelerate a few days prior to an eruption. 

Our experience with volcanoes, such as Mount St. Helens and those on the big island of Hawaii, suggests that earthquakes often provide the earliest warning of an impending volcanic eruption. In the case of Mount St. Helens, earthquake activity started in mid-March before the eruption in May. Activity began suddenly, with near-continuous shallow seismicity. Unfortunately, there was no increase in earthquakes immediately before the May 18 event. In Hawaii earthquakes have been used to monitor the movement of magma as it approaches the surface. Several months before the 1991 Mt. Pinatubo eruptions, small steam explosions and earthquakes began. Mt. Pinatubo (present elevation 1700 m, or 5578 ft) was an eroded ridge, and, as a result, did not have the classic shape of a volcano. Furthermore, it had not erupted in 500 years; most of the people living near it did not even know it was a volcano! Scientists began monitoring earthquake activity and studying past volcanic activity, which was determined to be explosive. Earthquakes increased in number and magnitude before the catastrophic eruption, migrating from deep beneath the volcano to shallow depths beneath the summit. 

Geophysicists have proposed a generalized model for seismic activity that may help in predicting eruptions. The model is for explosive composite volcanoes, such as those in the Cascade Mountains, which may awaken after an extended period of inactivity. As a dormant volcano reawakens, the magma must fracture and break previously solidified igneous rock above the magma chamber in order to work its way to the surface. Several weeks before an eruption, increasing pressure creates numerous fractures in the plugged volcano conduit above the chamber. At first, the increase in seismic events will be very gradual, and a seismologist may need 10 days or so to confidently recognize an accelerating trend toward an eruption. Once the trend has been recognized, there will still be several days before the eruption occurs. Unfortunately, this short warning time may be insufficient for a large-scale evacuation. Thus to forecast eruptions, it may be best to use seismic activity in concert with other eruption precursors discussed below. It is fortunate that, in contrast to earthquakes, volcanoes provide warning signs prior to eruption.

Thermal, Magnetic, and Hydrologic Monitoring 

Monitoring of volcanoes is based on the fact that, before an eruption, a large volume of magma moves up into some sort of holding reservoir beneath the volcano. The hot material changes the local magnetic, thermal, hydrologic, and geochemical conditions. As the surrounding rocks heat, the rise in temperature of the surficial rock may be detected by remote sensing or infra-red aerial photography. Increased heat may melt snowfields or glaciers; thus, periodic remote sensing of a volcanic chain may detect new hot points that could indicate potential volcanic activity. This method was used with some success at Mount St. Helens before the main eruption on May 18, 1980. When older volcanic rocks are heated by new magma, magnetic properties, originally imprinted when the rocks cooled and crystallized, may change. These changes can be detailed by ground or aerial monitoring of the magnetic properties of the rocks that the volcano is composed of.

Topographic Monitoring 

 Inflation and tilting before eruption (a) Idealized diagram of Kilauea, illustrating inflation and surface tilting, accompanied by earthquakes as magma moves up. (U.S. Geological Survey Circular 1073, 1992) (b) The actual data graph, showing the east west component and the north south component of ground tilt recorded from 1964 to 1966 on Kilauea Volcano, Hawaii. Notice the slow change in ground tilt before eruption and rapid subsidence during eruption. 

Monitoring topographic changes and seismic behaviour of volcanoes has been useful in forecasting some volcanic eruptions. The Hawaiian volcanoes, especially Kilauea, have supplied most of the data. The summit of Kilauea tilts and swells before an eruption and subsides during the actual outbreak. Kilauea also undergoes earthquake swarms that reflect moving subsurface magma and an imminent eruption. The tilting of the summit in conjunction with the earthquake swarms was used to predict a volcanic eruption in the vicinity of the farming community of Kapoho on the flank of the volcano, 45 km (28 mi) from the summit. As a result, the inhabitants were evacuated before the event, in which lava overran and eventually destroyed most of the village. Because of the characteristic swelling and earthquake activity before eruptions, scientists expect the Hawaiian volcanoes to continue to be more predictable than others. Monitoring of ground movements such as tilting, swelling, opening of cracks, or changes in the water level of lakes on or near a volcano has become a useful tool for recognizing change that might indicate a coming eruption. Today, satellite based radar and a network of Global Positioning System (GPS) receivers can be used to monitor change in volcanoes, including surface deformation, without sending people into a hazardous area.

Monitoring Volcanic Gas Emissions 

The primary objective of monitoring volcanic gas emissions is to recognize changes in the chemical composition of the gases. Changes in both gas composition that is, the relative amounts of gases such as steam, carbon dioxide, and sulphur dioxide and gas emission rates are thought to be correlated with changes in subsurface volcanic processes. These factors may indicate movement of magma toward the surface. This technique was useful in studying eruptions at Mount St. Helens and Mt. Pinatubo. Two weeks before the explosive eruptions at Mt. Pinatubo, the emissions of sulphur dioxide increased by a factor of about 10.

Geologic History 

Understanding the geologic history of a volcano or volcanic system is useful in predicting the types of eruptions likely to occur in the future. The primary tool used to establish the geologic history of a volcano is geologic mapping of volcanic rocks and deposits. Attempts are made to date lava flows and pyroclastic activity to determine when they occurred. These are the primary data necessary to produce maps depicting volcanic hazards at a particular site. Geologic mapping, in conjunction with the dating of volcanic deposits at Kilauea, Hawaii, led to the discovery that more than 90 percent of the land surface of the volcano has been covered by lava in only the past 1500 years. The town of Kalapana, destroyed by lava flows in 1990, might never have been built if this information had been known before development, because the risk might have been thought too great. The real value of geologic mapping and dating of volcanic events is that they allow development of hazard maps to assist in land-use planning and preparation for future eruptions. Such maps are now available for a number of volcanoes around the world. 

Volcanic Alert or Warning 

Geologic behavior, color-coded condition, and response: Volcanic Hazards Response Plan; Long Valley Caldera, California.

At what point should the public be alerted or warned that a volcanic eruption may occur? This is an important question being addressed by volcanologists. At present, there is no standard code, but one being used with various modifications has been developed by the U.S. Geological Survey. The system is colour coded by condition; each colour green, yellow, orange, and red denotes increasing concern. This table was created specifically for the Long Valley caldera in California. Similar systems have been or are being developed for other volcanic areas, including Alaska and the Cascade Mountains of the Pacific Northwest. The colour-coded system is a good start; however, the hard questions remain: When should evacuation begin? When is it safe for people to return? Evacuation is definitely necessary before condition red, but when, during conditions yellow or orange, should it begin?

Volcanic Features

Geologic features that are often associated with volcanoes or volcanic areas include craters, calderas, volcanic vents, geysers, and hot springs.

Craters, Calderas, and Vents 

Crater

Vent

Depressions commonly found at the top of volcanoes are craters. Craters form by explosion or collapse of the upper portion of the volcanic cone and may be flat floored or funnel shaped. They are usually a few kilometres in diameter. 

Calderas are gigantic, often circular, depressions resulting from explosive ejection of magma and subsequent collapse of the upper portion of the volcanic cone. They may be 20 or more kilometres in diameter and contain volcanic vents, as well as other volcanic features, such as gas vents and hot springs. Volcanic vents are openings through which lava and pyroclastic debris are erupted at the surface of Earth. 

Vents may be roughly circular conduits, and eruptions construct domes and cones. Other vents may be elongated fissures or rock fractures, often normal faults, which produce lava flows. Some extensive fissure eruptions have produced huge accumulations of nearly horizontal basaltic lava flows called flood basalts. The best-known flood basalt deposit in the United States is the Columbia Plateau region in parts of Washington, Oregon, and Idaho, where basalt covers a vast area.

Hot Springs and Geysers 

Hot springs and geysers are hydrologic features found in some volcanic areas. Groundwater that comes into contact with hot rock becomes heated, and, in some cases, the heated water discharges at the surface as a hot spring, or thermal spring. In rare cases, the subsurface groundwater system involves circulation and heating patterns that produce periodic release of steam and hot water at the surface, a phenomenon called a geyser. World-famous geyser basins or fields are found in Iceland, New Zealand, and Yellowstone National Park in Wyoming.

Caldera Eruptions 

Calderas are produced by very rare, but extremely violent, eruptions. Although none have occurred anywhere on Earth in the last few hundred thousand years, at least 10 caldera eruptions have occurred in the last million years, three of them in North America. A large caldera-forming eruption may explosively extrude up to 1000 cubic km (240 ) of pyroclastic debris, consisting mostly of ash. This is approximately 1000 times the quantity ejected by the 1980 eruption of Mount St. Helens! Such an eruption could produce a caldera more than 10 km (6.2 mi) in diameter and blanket an area of several tens of thousands of square kilometres with ash. These ash deposits can be 100 m (328 ft) thick near the craters rim and a meter or so thick 100 km (62 mi) away from the source.6 The most recent caldera-forming eruptions in North America occurred about 600,000 years ago at Yellowstone National Park in Wyoming and 700,000 years ago in Long Valley, California. The area covered by ash in the eruption event, which produced the Long Valley caldera near the famous Mammoth Mountain ski resort. The most recent volcanic eruptions at Long Valley were about 400 years ago. Measurable uplift of the land, accompanied by swarms of earthquakes up to M 6 in the early 1980s, suggested magma was moving upward, prompting the U.S. Geological Survey to issue a potential volcanic hazard warning that was subsequently lifted. However, the future of Long Valley remains uncertain. The main events in a caldera-producing eruption can occur quickly in a few days to a few weeks but intermittent, lesser-magnitude volcanic activity can linger on for a million years. Thus, the Yellowstone event has left us hot springs and geysers, including Old Faithful, while the Long Valley event has left us a potential volcanic hazard. In fact, both sites are still capable of producing volcanic activity because magma is still present at variable depths beneath the caldera floors. Both are considered resurgent calderas because their floors have slowly domed upward since the explosive eruptions that formed them. The most likely future eruptions for Long Valley or Yellowstone would be much smaller than the giant caldera eruptions that occurred hundreds of thousands of years ago.