What are the different types of basaltic lava flows and how do they form? | Volcano World | Oregon State University What are the different types of basaltic lava flows and how do they form? Pillow lavas are volumetrically the most abundant type because they are erupted at mid-ocean ridges and because they make up the submarine portion of seamounts and large intraplate volcanoes, like the Hawaii-Emperor seamount chain. Image Credit: Gordon Tribble/USGS Eruptions under water or ice make pillow lava. Pillow lavas have elongate, interconnected flow lobes that are elliptical or circular in cross-section. Pillow lavas are often considered important when trying to decipher old rock sequences because they indicate the presence of water. However, you have to be very careful to make sure that you are not looking at regular old pahoehoe toes, which of course, indicate dry land. Many of the features that supposedly can be used to tell the difference between the two don't always work. The only absolute way to know that you are looking at true pillow lavas is to find water-lain sediments between the individual pillows.

You might think "wait a minute, sediments are lain down really slowly, how are they going to get between the pillows while they're active?" Actually, when lava is flowing under water, there is a lot of sediment generated as pieces of the lava fall off during the rapid collapsing of the pillows as the quickly chill. Pillow lavas are essentially the underwater equivalent of pahoehoe. They form from low effusion-rate eruptions of fluid basalt lava. They have a rounder form than pahoehoe toes, mainly because of the ability of water to help buoy them up (gravity doesn't flatten them out so much). Also in contrast to pahoehoe toes, pillow lavas tend to have thicker skins of glass (because they are quenched more quickly), less vesicular skins (because even shallow water pressure is able to prevent bubbles from expanding very much), and generally radial fractures (in contrast to the generally concentric flow banding seen in pahoehoe toes). Nevertheless, it is often difficult to tell the two types of lava apart in exposures.

The only way to absolutely know that the flows you're looking at are pillow lavas rather than pahoehoe toes, is to find submarine sediments (such as hyaloclastite debris formed from the violent reaction of lava and water) between the pillows. Pillow lavas are also found near the summit of Mauna Kea These pillow lavas were produced by a subglacial eruption that occurred 10,000 years ago. The pillow is about 3 feet (1 m) in diameter and has a glassy rim. Figure 21.11 from Porter, 1987. . Pahoehoe lava is characterized by a smooth, billowy, or ropy surface. Pahoehoe flows tend to be relatively thin, from a few inches to a few feet thick. In map-view the flows tend to be narrow and elongate. Image Credit: Steve Mattox, 1989. (Kilauea) A'a A'a is characterized by a rough, jagged, spinose, and generally clinkery surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows.

During the early episodes of the current eruption of Kilauea volcano, aa flows up to 36 feet (11 m) thick surged through the Royal Gardens subdivision at rates as great as 108 ft/min (33 m/min). Image Credit: R. W. Decker/USGS July 02, 1983. The A'a / Pahoehoe difference: If lava cools slowly and does not move too fast it forms smooth ropy lava called pahoehoe. However, if it cools quickly and moves fast it can tear into clinkery pieces called a'a. Temperature and gases certainly influence whether the lava becomes aa or pahoehoe. Probably the two biggest factors are and rate of shear strain. Viscosity is just how sticky something is (how much it resists flowing). An example of rate of shear strain is how quickly or slowly force is applied across a deck of cards. Some factors influencing viscosity or rate of shear strain are listed below: temperature crystallinity channel configuration Peterson and Tilling (1980, p.

273) suggested two general conditions that determine whether pahoehoe or aa forms: If lava slows, cools, and stops in direct response to the corresponding increase in viscosity only, it retains its pahoehoe form. If lava is forced to continue flowing after a certain critical relationship> between viscosity and rate of shear strain is achieved, the lava changes to aa. Peterson and Tilling called this critical relationship the "transition threshold." They found that if the rate of shear strain is high, the transition threshold is reached at a lower viscosity than if the shear strain rate is low. The converse is also true. If the viscosity of the lava is high, a relatively low rate of shear strain may achieve the transition threshold, and the lava changes to a'a. People often ask if there is a compositional difference between aa and pahoehoe lava. There is no systematic chemical difference between aa and pahoehoe lava. Lavas with the identical compositions can form both aa and pahoehoe. Lavas that have slight chemical differences tend to have different temperatures and viscosity's but the critical factor influencing the transition from pahoehoe to aa is the viscosity of the lava.

Other lavas: The types of rock: igneous, metarmorphic and sedimentary The types of rock: igneous, metarmorphic and sedimentary 0 Mihai Andrei It’s the first thing you learn in a geology class – very briefly the three types of rocks are: Igneous; they form from the cooling of magma deep inside the earth. They often have large crystals (you can see then with the naked eye). Metamorphic; they are formed through the change (metamorphosis) of igneous and sedimentary rocks. They can form both underground and at the surface. Sedimentary; they are formed through the solidification of sediment. They can be based off of organic remains (such as limestone), or just form from the cementing of other rocks. Now, the long story, which is much more interesting, is this: Igneous Rocks Lava flow on Hawaii. Lava is the extrusive equivalent of magma. Image via Wiki Commons. The key element for igneous rocks is magma; magma is a mixture of molten or semi-molten rock, as well as some gases and other volatile elements.

The deeper you go underground, the hotter it gets, and if you go deep enough, you reach the mantle – which can be though of as a huge layer of magma surrounding the Earth’s core. As you probably know, when magma cools, it turns into rock; if it cools in the underground, at higher temperatures (but still lower than that of the magma), the cooling process will take slowly, and crystals will have time to develop. That’s why you see rocks such as granite with big crystals – because the magma had time to cool off. The crystals are also differentiated, as you can see below. Note the white, almost rectangular feldspar crystals, the grey virtually shapeless quartz crystals, and the black crystals, which can be either black mica or amphibole. Image modified from Eastern Illinois University. However, if the magma erupts or is cooled rapidly, then you get what is called a volcanic rock – not really igneous, but also originating from lava. The classical example here is basalt – small crystals, or very few large ones. Volcanic rocks are also called extrusive igneous rocks, as opposed to intrusive igneous rocks. Some volcanic rocks (like obsidian) don’t have any crystals at all.

Basalt – note the almost complete lack of visible crystals. Now compare it to the granite. Image via Georgia State University. Science ROCKS! Uhm.. get it? join our community! Pumice. Not all magma is made equal though – different magmas can have different chemical compositions, different quantities of gases and different temperatures; different magmas -> different rocks. That’s why you get this incredible variety. There are over 700 hundred types of igneous rocks, and they are generally the hardest and heaviest (densest) of all rocks. However, volcanic rocks can be incredibly lightweight – pumice for example can even float, and was called by ancient sailors “the foam of the sea”. This happens when a volcano violently erupts, creating pockets of air in the rock. The most common types of igneous rocks are: andesite volcanic bomb Metamorphic Rocks Here, the name says it all – these are rocks that underwent a metamorphosis; they changed. They were either sedimentary or igneous (or even metamorphic), and they changed so much, that they are fundamentally different from the initial rock. Different types of metamorphism. Image via Tankon Yvtar.

There are two types of metamorphism (change) that can cause this: contact metamorphism (or termic metamorphism); the rocks are so close to magma that they start to partially melt and change their properties. You can have recrystallization, fusing between crystals and a lot of chemical reactions. Temperature is the main driver here. regional metamorphism (or dynamic metamorphism); this typically happens when rocks are deep underground and they are subjected to massive pressure – so much that they often become elongated and the original features are destroyed. Pressure (often times with temperature) is the main driver here. Folded foliation in a metamorphic rock from near Geirangerfjord, Norway. Image via Wiki Commons. Metamorphic rocks can have crystals and minerals both from the initial rocks, and new minerals resulting from the metamorphosis process. However, some minerals are clear indicators of a metamorphic process. Among these, the most usual ones are: garnet, chlorite and kyanite.

Equally as significant are changes in chemical environment that result in two metamorphic processes: mechanical dislocation (the rock or some minerals are physically altered) and chemical recrystallization (when the temperature and pressure changes, some crystals aren’t stable, and they change into other crystals). Marble is a non-foliated metamorphic rock. Advertisement They can be divided into many categories, but they are typically split into: Foliated metamorphic rocks; where pressure squeezes or elongates the crystals and they have a clear preferential allignment. Non-foliated metamorphic rocks; where the crystals have no preferential allignment. Some rocks, such as limestone are made of minerals that simply don’t elongate, no matter how much stress you apply. Metamorphic rocks can form in different conditions, in different temperatures (up to 200 °C) and pressures (up to 1500 bars). Simply by being buried deep enough for a long enough time, a rock will become metamorphic. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion; they are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth’s interior.

The most common metamorphic rocks are: amphibolite schist (blueschist, greenschist, micaschist, etc) A micaschist. The dark brown rounded minerals are garnet, and everything you see with a whiteish tint is the mica. The reddist areas are rusty mica. Image modified from Willowleaf Minerals. eclogite slate Sedimentary Rocks Sedimentary rocks are called that because they were once sediment. Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently naturally transported (or not). Sedimentary rocks from through deposition of material at the Earth’s surface and within bodies of water. A conglomerate – a rock made from cemented gravel. Image via Earth Physics Teaching. Sedimentary rocks are quite difficult to classify, as you can look at the situation from many different angles (the chemical make-up, the sedimentation process, organic/anorganic material), but the most common classification is the following: clastic sedimentary rocks; basically small rock fragments (many silicates) transported and deposited by fluids (water, bed flows).

These rocks are further classified on the size and composition of the clastic crystals included in the sedimentary rocks (most often quartz, feldspar, mica and clay). conglomerates (and breccias); conglomerates are dominantly composed of rounded gravel, while breccias are composed of angular (sharper) gravel. sandstones; as the name says it, it’s a rock made from many-sand-sized minerals and rock grains. The most dominant mineral in sandstones is quartz, because it is the most common mineral in the Earth’s surface crust. An old, red sandstone. Image via Ian Hopkinson. mudrocks; again, the name says it all – rocks made from solidified mud. They typically contain very fine particles and are transported as suspended particles by turbulent flow in water or air, depositing once the flow settles. biochemical rocks; you’ll probably be surprised to find out that most limestone on the face of the Earth comes from biological sources. In other words, most limestone you see today comes from the skeletons of organisms such as corals, mollusks, and foraminifera. Coal is another example of biochemical rock.

chemical rocks; these rocks include gypsum and salt (halite) – formed mostly through water evaporation Yes, salt is a mineral – and it can be quite beautiful. The rock is called halite in this context and it’s a sedimentary rock. There are also other type of specific sedimentary rocks, like for example the ones formed in hot springs. Most of the solid surface of our planet (very roughly 70%) is represented by sedimentary rocks – but if you start to go deep enough, they are replaced by igneous and metamorphic. As I mentioned with the biochemical rocks, fossils can become rocks in time. You can actually have entire mountains made up from reefs, like you can see below. This entire mountain in Romania was formed based on a coral reef. Image via MP Interactiv Some common sedimentary rocks are: argilite Rocks, Rock Information, Facts, News, Photos -- National Geographic Space Photograph by Jim Richardson Rocks are so common that most of us take them for granted—cursing when we hit them with the garden hoe or taking advantage of them to drive in tent pegs on summer camping trips. But what exactly is a rock?

To geologists, a rock is a natural substance composed of solid crystals of different minerals that have been fused together into a solid lump. The minerals may or may not have been formed at the same time. What matters is that natural processes glued them all together. There are three basic types of rock: igneous, sedimentary, and metamorphic. Extremely common in the Earth's crust, igneous rocks are volcanic and form from molten material. They include not only lava spewed from volcanoes, but also rocks like granite, which are formed by magma that solidifies far underground. Typically, granite makes up large parts of all the continents. The seafloor is formed of a dark lava called basalt, the most common volcanic rock. Basalt is also found in volcanic lava flows, such as those in Hawaii, Iceland, and large parts of the U.S. Northwest. Granite rocks can be very old. Some granite, in Australia, is believed to be more than four billion years old, although when rocks get that old, they've been altered enough by geological forces that it's hard to classify them. Sedimentary rocks are formed from eroded fragments of other rocks or even from the remains of plants or animals.

The fragments accumulate in low-lying areas—lakes, oceans, and deserts—and then are compressed back into rock by the weight of overlying materials. Sandstone is formed from sand, mudstone from mud, and limestone from seashells, diatoms, or bonelike minerals precipitating out of calcium-rich water. Fossils are most frequently found in sedimentary rock, which comes in layers, called strata. Metamorphic rocks are sedimentary or igneous rocks that have been transformed by pressure, heat, or the intrusion of fluids. The heat may come from nearby magma or hot water intruding via hot springs. It can also come from subduction, when tectonic forces draw rocks deep beneath the Earth's surface. Marble is metamorphosed limestone, quartzite is metamorphosed sandstone, and gneiss, another common metamorphic rock, sometimes begins as granite. Basalt: Igneous Rock - Pictures, Definition, Uses & More Basalt What Is Basalt, How Does It Form, and How Is It Used? Basalt: A fine-grained igneous rock that is usually black in color. The specimen shown is about two inches (five centimeters) across. What is Basalt?

Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies, such as an igneous dike or a thin sill. It has a composition similar to gabbro . The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock. Olympus Mons Volcano: This shield volcano is composed of basalt and has enormous calderas at the summit. Olympus Mons is the highest topographic feature on Mars and is the largest known volcano in our solar system. It is about 375 miles (600 kilometers) in diameter and 15 miles (25 kilometers) high. NASA Mars Orbiter Camera image. Earth's Most Abundant Bedrock Basalt underlies more of Earth's surface than any other rock type. Most areas within Earth's ocean basins are underlain by basalt. Although basalt is much less common on continents, lava flows and flood basalts underlie several percent of Earth's land surface.

Basalt is a very important rock. Basalt on Moon and Mars Basalt is also an abundant rock on the Moon. Much of the Moon's surface is underlain by basaltic lava flows and flood basalts. These areas of the Moon are known as "lunar maria." Large areas of the Moon have been resurfaced by extensive basalt flows which may have been triggered by major impact events. The ages of lunar maria can be estimated by observing the density of impact craters on their surface. Younger basalt flows will have fewer craters. Olympus Mons is a shield volcano on Mars. It, like most other volcanic features on Mars, was formed from basaltic lava flows. It is the highest mountain on Mars and is the largest known volcano in our solar system. Basalt-Forming Environments: This map shows the location of oceanic divergent boundaries and hotspots. These are locations where large volumes of basalt have been formed. Map copyright by Geology.com and MapResources. Locations generalized after United States Geological Survey, Geologic Investigations Map I-2800: This Dynamic Planet.

Igneous rock composition chart: This chart shows that basalt is typically composed of pyroxenes, plagioclase, micas, and amphiboles. Basalt-Forming Environments Most of the basalt found on Earth was produced in just three rock-forming environments: 1) oceanic divergent boundaries , 2) oceanic hotspots , and 3) mantle plumes and hotspots beneath continents . The images on this page feature some of these basalt-forming environments. Sea floor pillow basalts on the Juan de Fuca Ridge, a divergent plate boundary located about 150 miles (240 kilometers) west of the Washington-Oregon coast. This lava flow, produced by a fissure eruption, was about five years old when the photograph was taken. NOAA Ocean Explorer image. Hawaii Basalt Flows: Lava flows dump into the Pacific Ocean on the coast of Hawaii. Multiple locations where hot lava streams into the ocean can be seen in this image along with a red-hot lava flow traversing the lava field. This photo shows the enormous extent of the flows. They extend from the shoreline up to the horizon.

A volcanic plume from the Pu`u `O`o vent can be seen over the horizon near the center of the image. The lava in these flows originated from the Pu`u `O`o vent. USGS image. Basalts at Oceanic Divergent Boundaries Most of Earth's basalt is produced at divergent plate boundaries on the mid-ocean ridge system (see map). Here convection currents deliver hot rock from deep in the mantle. This hot rock melts as the divergent boundary pulls apart, and the molten rock erupts onto the sea floor. These submarine fissure eruptions often produce pillow basalts as shown in the image on this page. The active mid-ocean ridges host repeated fissure eruptions. Most of this activity is unnoticed because these boundaries are under great depths of water. At these deep locations, any steam, ash, or gas produced is absorbed by the water column and does not reach the surface. Earthquake activity is the only signal to humans that many of these deep ocean ridge eruptions provide. However, Iceland is a location where a mid-ocean ridge has been lifted above sea level. There, people can directly observe this volcanic activity.

Thermal image of a hot basalt flow on the flank of Hawaii's Kilauea volcano. Hot lava at the front of the flow is revealed in yellow, orange and red colors. The channel that it flowed through on the previous day appears as a purple and blue track. United States Geological Survey image. Oceanic Hotspots Another location where significant amounts of basalt are produced is above oceanic hotspots. These are locations (see map above) where a small plume of hot rock rises up through the mantle from a hotspot on Earth's core. The Hawaiian Islands are an example of where basaltic volcanoes have been built above an oceanic hotspot. Basalt production at these locations begins with an eruption on the ocean floor. If the hotspot is sustained, repeated eruptions can build the volcanic cone larger and larger until it becomes high enough to become an island. All of the islands in the Hawaiian Island chain were built up from basalt eruptions on the sea floor. The island that we know today as "Hawaii" is thought to be between 300,000 and 600,000 years old. It began as an eruption on the floor of the Pacific Ocean.

The volcanic cone grew as recurrent eruptions built up layer after layer of basalt flows. About 100,000 years ago it is thought to have grown tall enough to emerge from the ocean as an island. Today it consists of five overlapping volcanoes. Kilauea is the most active of these volcanoes. It has been in amost continuous eruption since January, 1983. Basalt flows from Kilauea have extruded over one cubic mile of lava, which currently covers about 48 square miles of land. These flows have travelled over seven miles to reach the ocean, covering highways, homes and entire subdivisions that were in their path. Columbia River Flood Basalts: The Columbia River Flood Basalts are an extensive sequence of stacked lava flows that reach a cumulative thickness of up to 6000 feet. The outcrops in the foreground and in the distance of this photo are all made up of layered basalt flows. Although basalt is typically a dark black rock, it often weathers to a yellow-brown color similar to the rocks shown here. Public domain image by Williamborg.

Columbia River Flood Basalts Map: A map of the area underlain by the Columbia River Flood Basalts in Washington, Oregon, and Idaho. The area shown is what has not yet been eroded away - the original extent of these basalt flows was much greater. Over 300 individual flows have been identified, and several hundred meters of basalt underlies much of the area shown in the map above. Map © by Geology.com and MapResources.com. Plumes & Hotspots Below Continents The third basalt-forming environment is a continental environment where a mantle plume or hotspot delivers enormous amounts of basaltic lava through the continental crust and up to Earth's surface. These eruptions can be from either vents or fissures. They have produced the largest basalt flows on the continents. The eruptions can occur repeatedly over millions of years, producing layer after layer of basalt stacked in a vertical sequence (see outcrop photo). The Columbia River Flood Basalts in Washington, Oregon, and Idaho are an example of extensive flood basalts on land (see map below).

Other examples include the Emeishan Traps of China, the Deccan Traps of India, the Keweenawan Lavas of the Lake Superior region, the Etendeka Basalts of Namibia, the Karroo Basalts of South Africa, and the Siberian Traps of Russia. (The word "traps" is derived from the Swedish word for "stairs," which describes the outcrop profile of these layered basalt deposits, as shown in the outcrop photo.) Rock & Mineral Kits: Get a rock, mineral, or fossil kit to learn more about Earth materials. The best way to learn about rocks is to have specimens available for testing and examination. The Roman theatre: (left) in Bosra, Syria. The dark building stone is basalt. Image © iStockphoto / Steve Estvanik. Basalt paving stones: (right) on a city street in Rome, Italy. Basalt pavers were often used in areas close to volcanoes. Image © iStockphoto / Giovanni Rinaldi. Uses of Basalt Basalt is used for a wide variety of purposes. It is most commonly crushed for use as an aggregate in construction projects.

Crushed basalt is used for road base, concrete aggregate, asphalt pavement aggregate, railroad ballast, filter stone in drain fields, and may other purposes. Basalt is also cut into dimension stone. Thin slabs of basalt are cut and sometimes polished for use as floor tiles, building veneer, monuments, and other stone objects. Volcano Types Volcano Types Volcano Types The U.S. Geological Survey estimates that there are about 65 active volcanoes in the United States and its territories. The Dynamic maps viewer (shown at right) provides an interactive presentation of potentially active volcanoes in the 48 continguous states. Volcanoes are distinguished by their eruption style, composition, and structure. Volcanoes act differently and form differently because they are made up of different types of rocks and minerals. Below is a description of common volcano types that can be recognized as distinguishable land formations. For more than 200 years keen observers have noted that some volcanic eruptions affect weather and climate. Scientists report that large eruptions at low latitudes can cause the greatest global climate change. Weaker eruptions send their eruptive materials only into the troposphere, where wind and rain quickly remove them.

High latitude eruptions send their materials into only one hemisphere. Based on this information and the nature of different volcano types presented below, do you think that certain types of volcanoes are more likely to cause climate change when they erupt? See if you can answer this question as you investigate the relationship between volcanoes and climate change. Volcanoes have many shapes and sizes, but the following three types are most important: stratovolcanoes, shields, and supervolcanoes. Use the Dynamic map tool to find further illustrations of volcanoes described in this overview of volcano types. Stratovolcanoes (Composite Volcanoes) Many of Earth's most beautiful mountains are stratovolcanoes—also referred to as composite volcanoes. The stratovolcanoes are made up of layers of lava flows interlayed with sand- or gravel-like volcanic rock called cinders or volcanic ash. These volcano land formations are typically 10-20 miles across and up to 10,000 or more feet tall. This type of volcano has steeper slopes of 6-10 degrees on its flanks and as much as a 30 degree slope near the top.

Stratovolcanoes show interlayering of lava flows and typically up to 50 percent pyroclastic material, which is why they are sometimes called composite volcanoes. Pyroclastic flows are high-density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds. They may result from the explosive eruption of molten or solid rock fragments, or both. They may also result from the nonexplosive eruption of lava when parts of dome or a thick lava flow collapses down a steep slope. Most pyroclastic flows consist of two distinguishable flowing mixtures: a basal flow of coarse fragments that moves along the ground and a turbulent cloud of ash that rises above the basal flow. Ash may fall from this cloud over a wide area downwind from the pyroclastic flow. Referring to the images below, the diagram shows how a composite or stratovolcano is “built” on the inside, and the photograph represents an example of an actual stratovolcano. Image above at left: A schematic representation of the internal structue of a typical stratovolcano (composite volcano). Image source: USGS publications .

Image above at right: Mayon, a stratovolcano in the Philippines. Image source: . Shield Volcanoes The second type may be familiar to you from news reports from Hawaii: the shield volcano. This type of volcano can be hundreds of miles across and 10,000 feet high. A shield volcano is characterized by gentle upper slopes (about 5 degrees) with somewhat steeper lower slopes (about 10 degrees). The shield volcanoes are almost entirely composed of relatively thin lava flows built up over a central vent. These features are illustrated in the shield volcano diagram shown below. Shield volcanoes have small amounts of pyroclastic material, most of which accumulates near the eruptive vents, resulting from fire fuming events. Thus, shield volcanoes typically form from nonexplosive eruptions of low viscosity basaltic magma. The individual islands of the state of Hawaii are simply large shield volcanoes. Mauna Loa, a shield volcano on the "big" island of Hawaii, is the largest single mountain in the world, rising more than 30,000 feet above the ocean floor and reaching almost 100 miles across at its base.

Shield volcanoes have low slopes and consist almost entirely of lavas. They almost always have large calderas at their summits. The graphic at left illustrates the internal structure of a typical shield volcano. Image source: Calderas: A Landform at the Summit of Shield and Stratovolcanoes Both strato/composite and shield volcanoes can lose their tops following a series of tremendous explosions. The change in these volcanoes' structure is visible as a large depression at the shield or stratovolcano summit. After enormous volumes of volcanic ash and dust are expelled and swept down the slopes as ash and avalanches, these large volume explosions rapidly drain in magna beneath the mountain and can no longer support the volcano top. The collapsing top forms a large depression in the landscape, which may later fill with water to form a lake. Similarly, the tops of shield volcanoes collapse when magma erupts as lava flows, emptying the magma chambers. The steep-walled, basin-shaped depressions formed by the collapse of volcanoes are called calderas. Calderas by definition are larger than 1.5 miles in diameter and can range up to 15 miles wide or as huge elongated depressions as much as 60 miles long.

The two images below show two very different caldera land formations. Image above at left: Crater Lake, Oregon; Wizard Island, a cinder cone, rises above the lake surface. Image source: USGS publications . Image above at right: This Ikonos image, taken on Jan. 14, 2003, shows Kilauea’s summit caldera, the surface of which is covered in fresh lava flows. The newer flows are dark, while the older flows pale as the iron in the lava oxidizes into rust. The oldest flow in the caldera is from 1882. The Halema`uma`u crater forms a pale circle in the southwest section of the caldera. As recently as 1924, the crater was filled with a molten lava lake. Image source: NASA Earth Observatory . Supervolcanoes While ordinary volcanoes can kill thousands of people and destroy entire cities, scientists believe that a supervolcano explosion is big enough to affect everyone on the planet. Although they're called "super," most people would have trouble spotting a supervolcano before it erupts.

The main feature of supervolcanoes is a large magma chamber, which is an underground reservoir filled with flowing, hot rock under huge pressures. Afer their eruption ash has been blown so far away that no mountain exists, and commonly the area is low and lake-filled. A supervolcanic eruption is rare. The last one occurred at Toba, Indonesia, about 74,000 years ago. Geologists think these eruptions take place about every 50,000 years. About 40 supervolcanoes are identified across the globe, but fortunately no supervolcano eruption has occured in the last 1,000 years. Yellowstone, located in Wyoming, is a dormant supervolcano, which means a major eruption could happen in the future. The Yellowstone National Park lies within the Yellowstone Caldera, a collapse hat formed during a super eruption 640,000 years ago. Heat from magma beneath the caldera still fuels some 10,000 geothermal features (geysers and hot springs)—that's half of the world total. The map above at left of the Yellowstone supervolcano shows the lava flows.

The flow is dated to be 72,000 years old and to have erupted as a single event. Other flows were likely formed from multiple eruptions. Photo credit: USGS/Yellowstone Volcano Observatory. The image above at right shows steam rising from Castle Geyser in Yellowstone National Park. Image source: Yellowstone National Park (file photo): Photograph by Mark Thiessen, National Geographic. Cinder Cone Volcanoes An easily recognized type of volcano is the cinder cone. As you might expect from the name, these volcanoes consist almost entirely of loose, grainy cinders consisting typically of basaltic and andesitic material and almost no lava. They are small volcanoes, usually only about a mile across and up to about 1,000 feet high. They have very steep sides and usually have a small crater on top. Often cinder cones are classed as a major type of volcano. But cinder cones are much smaller than most shield, composite, and ash flow volcanoes. In fact, cinder cones occur on all of these larger volcano types. Image at left: A schematic representation of the internal structure of a typical cinder cone. Image source: USGS publications .

Image at right: Cinder cone volcano near Veyo, Utah. Image source: . More Volcano Types Maars, lava domes, geysers, fumaroles, hot springs, and pateau basalts are also volcanic land forms caused by different geological processes that form them and control their activities once these different geophysical structures are formed. These and the other volcanic stuctures described above are characterized by the types of materials they are made of, which results from prior eruptive behavior of the volcano. Explore how geologists study and classify volcanic eruptions and landforms with these additional resources: The Volcano Hazards Program at USGS: Earth Observatory: Volcano Images and Features: Can You Recognize Types of Volcanoes? What types of volcanoes are seen in this image of Russia’s Kamcharka Peninsula? Hint: Look closely. There are two stratovolcanoes, one shield volcano, and one volcano that appears to be formed from overlapping stratovolcanoes. View image with volcano types identified in the Volcanoes Featured Data section. This image was taken by an astronaut of the Expedition 25 crew from the International Space Station.

Igneous Rocks Lesson #12 | Volcano World | Oregon State University Igneous Rocks Lesson #12 or in the lowest areas of the crust usually at a depth of 50 to 200 kilometers. ash produce volcanoes. The lava that reaches the Earth's surface will harden and become igneous rock. When the magma does not reach the surface it produces a variety of geologic structures. When lava reaches the surface of the Earth through volcanoes or through great , and volcanic ash and dust. This is the volcano Paricutin that is located in Mexico. It is erupting cinders and pumice which are examples of extrusive igneous rocks. Millions and even billions of years ago molten rock was cooling and thus hardening into igneous rocks deep under the surface of the Earth. These rocks are now visible because mountain building has thrust them upward and erosion has removed the softer rocks exposing the much harder igneous rocks. These are called intrusive igneous rocks because the magma has intruded into pre-exiting rock layers. Types of intrusive igneous rocks are granite and basalt . The diagram above shows you a large intrusive igneous body called a batholith. A batholith is the largest of the intrusive bodies.

They are larger than 100 square kilometers and usually form granite cores. As you can see in the diagram above a batholith is a very large intrusive igneous body. There are two types of intrusive bodies that we are going to discuss 1)Discordant and 2) Concordant. A discordant igneous rock body cuts across the pre-exiting rock bed. Batholiths and dikes are examples of discordant rock bodies. A dike is a vertical or near vertical intrusive igneous rock body that cuts across rock beds. They frequently form from explosive eruptions that crack the area around a volcano with the magma filling the cracks forming a dike. A concordant igneous rock body runs parallel to the pre-existing bedrock. Laccoliths and sills are examples of concordant igneous rock bodies. A laccolith is a Rhyolite and granite are the two most common types of acidic rock. Intermediate rocks contain between 53% and 65% silica. They also contain potassium and plagioclase feldspar with a small amount of quartz. Diorite and are the two most common types of intermediate rock.

Basic rocks are composed of less than 52% silica and a large amount of plagioclase feldspar and very rarely quartz. The two most common types of basic rocks are basalts and gabbros. Ultrabasic rocks are composed of less than 45% silica and contain no quartz or feldspar. They are composed mainly of the minerals olivine and pyroxene. The most common ultrabasic rock is periodite. Periodite is a dark green, coarse-grained igneous rock that many scientists believe is the main rock of the mantle. Basalts are dark colored, fine-grained extrusive rock. The mineral grains are so fine that they are impossible to distinguish with the naked eye or even a magnifying glass. They are the most widespread of all the igneous rocks. Most basalts are volcanic in origin and were formed by the rapid cooling and hardening of the lava flows. Some basalts are intrusive having cooled inside the Earth's interior. formation . When basaltic lava cools it often forms hexagonal (six sided) columns.

Some famous examples of columnar basalt formations are the Columbia Plateau overlooking the Columbia River near Portland, the Giant's Causeway in Northern Ireland, and the Devils Postpile National Monument in California (Above). Pumice is a very light colored, frothy volcanic rock. Pumice is formed from lava that is full of gas. The lava is ejected and shot through the air during an eruption. As the lava hurtles through the air it cools and the gases escape leaving the rock full of holes. Pumice is so light that it actually floats on water. Huge pumice blocks have been seen floating on the ocean after large eruptions. Some lava blocks are large enough to carry small animals. Pumice is ground up and used today in soaps, abrasive cleansers, and also in polishes. Rhyolite is very closely related to granite. The difference is rhyolite has much finer crystals. These crystals are so small that they can not be seen by the naked eye. Rhyolite is an extrusive igneous rock having cooled much more rapidly than granite giving it a glassy appearance.

The minerals that make up rhyolite are quartz, feldspar, mica, and hornblende. Gabbros are dark-colored, coarse-grained intrusive igneous rocks. They are very similar to basalts in their mineral composition. They are composed mostly of the mineral plagioclase feldspar with smaller amounts of pyroxene and olivine. Obsidian is a very shiny natural volcanic glass. When obsidian breaks it fractures with a distinct conchoidal fracture. Notice in the photo to the left how it fractures. Obsidian is produced when lava cools very quickly. The lava cools so quickly that no crystals can form. When people make glass they melt silica rocks like sand and quartz then cool it rapidly by placing it in water. Obsidian is produced in nature in a similar way. Obsidian is usually black or a very dark green, but it can also be found in an almost clear form. Ancient people throughout the world have used obsidian for arrowheads, knives, spearheads, and cutting tools of all kinds. Today obsidian is used as a scalpel by doctors in very sensitive eye operations. Write the answers to the following questions in complete sentences on a piece of paper.

In your own words write a definition for magma and lava. 2. What is the difference between intrusive and extrusive igneous rocks? 3. What are the most common extrusive and intrusive igneous rocks? 4. What is the difference between granite and rhyolite and how are they similar? USGS: Volcano Hazards Program Volcano Hazards Program Lava flows destroy everything in their path. La va flows typically move slowly enough to outrun them, but they will destroy everything in their path. Lava type dictates flow shape and travel distance. Lava flows are streams of molten rock that pour or ooze from an erupting vent . Lava is erupted during either nonexplosive activity or explosive lava fountains . The speed at which lava moves across the ground depends on several factors, including (1) type of lava erupted and its viscosity; (2) steepness of the ground over which it travels; (3) whether the lava flows as a broad sheet, through a confined channel, or down a lava tube ; and (4) rate of lava production at the vent. Fluid basalt flows can extend tens of kilometers from an erupting vent .

The leading edges of basalt flows can travel as fast as 10 km/h (6 mph) on steep slopes but they typically advance less than 1 km/h (0.27 m/s or about 1 ft/s) on gentle slopes. But when basalt lava flows are confined within a channel or lava tube on a steep slope, the main body of the flow can reach velocities >30 km/h (19 mph). Viscous andesite flows move only a few kilometers per hour (couple feet per second) and rarely extend more than 8 km (5 mi) from their vents . Viscous dacite and rhyolite flows often form steep-sided mounds called lava domes over an erupting vent . Lava domes often grow by the extrusion of many individual flows >30 m (100 ft) thick over a period of several months or years. Such flows will overlap one another and typically move less than a few meters per hour. Lava flows may instigate other types of hazards. Everything in the path of an advancing lava flow will be knocked over, surrounded, buried, or ignited by the extremely hot temperature of lava .

When lava erupts beneath a glacier or flows over snow and ice, meltwater from the ice and snow can result in far-reaching lahars . If it enters a body of water or water enters a lava tube , the water may boil violently and cause an explosive shower of molten spatter over a wide area. Methane gas, produced as lava buries vegetation, can migrate in subsurface voids and explode when heated. Thick viscous lava flows, especially those that build a dome , can collapse to form fast-moving pyroclastic flows . Deaths caused directly by lava flows are uncommon because most move slowly enough that people can move out the way easily. Death and injury can result when onlookers approach an advancing lava flow too closely or their retreat is cut off by other flows. Deaths attributed to lava flows are often due to related causes, such as explosions when lava interacts with water, the collapse of an active lava delta that forms where lava enters a body of water, asphyxiation due to accompanying toxic gases, pyroclastic flows from a collapsing dome , and lahars from meltwater.

Other natural phenomena such as hurricanes, tornadoes, tsunami , fires, and earthquakes often destroy buildings, agricultural crops, and homes, but the owner(s) can usually rebuild or repair structures and their businesses in the same location. Lava flows, however, can bury homes and agricultural land under tens of meters of hardened black rock; landmarks and property lines become obscured by a vast, new hummocky landscape. People are rarely able to use land buried by lava flows or sell it for more than a small fraction of its previous worth.

Question: What is the most common type of rock formed from lava flows?
Answer: Basalt