VOLCANO REVIEW Review Questions:1. On what kind of plate boundaries do volcanoes appear?2. What is the difference between magma and lava?
THREE TYPES OF VOLCANOES: *There are three types of volcanoes: *Shield Volcano *Cinder cone Volcano *Stratovolcano
*WHY DO WE HAVE DIFFERENT TYPES OFVOLCANOES? The process of magma formation is different at each type of plate boundary. Therefore, the composition of magma differs in each tectonic setting. *Tectonic settings determine the types of volcanoes that form and the types of eruptions that take place.
*SHIELD VOLCANO Form from many layers of “runny” lava. Very wide, not too steep. Biggest type of volcanoes Tallest mountain in the world is Mauna Kea (measures from sea floor to top) non explosive eruptions
TECTONIC SETTING (LOCATIONS) Darwin, a shield volcano in the Galapagos Islands.Shield-type volcanoes are almost exclusively located in an oceanicsetting, in the “middle” of oceanic basins or as isolated islands,typically somewhat distant from continental shorelines.
MORPHOLOGY (SHAPE and SIZE) Fernandina, a shield volcano in the Galapagos Islands.Shield volcanoes tend to have very gentle (low-angle) slopes,sometimes referred to as the “overturned soupbowl” profile.Although not as visually dramatic as stratovolcanoes, they aregenerally much larger, particularly in diameter.
ACTIVITY Continued; San Martin, a small shield volcano off the coast of Baja, California.These volcanoes can form during single long-term effusive eruptionsand remain active for tens to hundreds of thousands of years. Duringtheir lifespans, dormant intervals may also last thousands to tens ofthousands of years.
*CINDER CONE VOLCANO Smallest type of volcano Most common Made from pyroclastic material (material shot out of a volcano) Form a large crater Explosive!
CINDER CONESCinder cones, also known as scoria cones, represent the smallest typeof volcano, rarely exceeding ~1000 ft in height. They are entirelycomposed of pyroclastic materials (volcanic ash). They are quitecommon and associated with both composite or shield volcanoes.They typically occur on the flanks (sides) of these volcanoes wheresecondary vents or fissures have opened up. Scoria cone near the summit of Mauna Kea, Hawaii.La Poruna, ChileSunset crater, Arizona
CINDER CONESA small cinder cone (~225m high, ~200m in diameter) located onBarren Island, a part of the Andaman Islands chain situated justnorth of Indonesia.
CINDER CONESKwohl Butte cinder cone is one of a chain of small cones trendingsouth of Mt. Bachelor (a composite volcano) in the Cascade range ofOregon. It is ~ 12,000 years old.
CINDER CONESThe Cerro Negro cinder cone represents one of Nicaragua’s youngestvolcanoes. It was born in April of 1850 and has grown to a height of250 m.
*STRATOVOLCANO OR COMPOSITE VOLCANO: Eruptions alternate between explosive and non-explosive. Sometimes they have runny lava layers, other times the have pyroclastic materials form layers. Have a wide base and steep sides. Have a crater Mount Fuji
MORPHOLOGY (SHAPE and SIZE) Mayon, the most active composite volcano in the Philippines.Stratovolcanoes are what most people associate with the wordvolcano. These towering peaks rise hundreds to several thousandmeters above their surroundings, often visually dominating thelandscape around them. They tend to be steep-sloped.
MORPHOLOGY (SHAPE and SIZE) Continued; Niragongo, an active composite volcano located on the border of Rwanda and Zaire, East Africa.The relatively steep profile of stratovolcanoes are due to their rockmakeup. They are formed of stratified layers of both viscous lavaflows and fragmental material (volcanic ash).
ACTIVITY Kamen (left) and Kliucheyskoi, two of Kamchatka’s highest composite volcanoes.Due to the viscous nature of the lavas associated with compositevolcanoes, they tend to “plug” up. If the pressures are great enough,these volcanoes may literally “blow their top”, and can be quiteviolent and dangerous!
ACTIVITY Continued; Colima, Mexico’s most active composite volcano.Some stratovolcanoes may form in a few thousand years, but remainactive for tens to hundreds of thousands of years. During theirlifespans, dormant intervals may also last tens of thousands of years.
*2 TYPES OF ERUPTIONS *Explosive: volcanoes that build enough pressure to blow its top, sending pyroclastic material into the air. *Non explosive: Build only enough pressure to allow lava to run down its sides.
NON EXPLOSIVE ERUPTION Mafic: refers to rocks and magma rich in iron and magnesium. This type of lava that is very runny. As magma nears the surface there is little pressure, causing gasses escape easily. Magma low in Silica have quiet eruptions
EXPLOSIVE ERUPTIONS Felsic: means magma with high silica and feldspar content. Felsic magma traps water and gas bubbles, which leads to lots of pressure. Silica acts like a cork Explosive eruptions are caused by a build up of high pressure. Convergent zones contain lots of water, therefore have explosive eruptions.
*PYROCLASTIC MATERIALS *Material that is thrown into the air during an explosion. *Volcanic bombs: large blobs of magma that harden in the air. Lapilli: pebble size rocks Volcanic ash: tiny powder like material
*FOUR TYPES OF LAVA Aa: lava that is thick and sharp Pahoehoe: lava that forms thin crust and wrinkles Pillow lava: lava that erupts under water, has a round shape Blocky lava: cooler, lava that does not travel far from eruption, jagged when it dries.
*PAHOEHOE: *lava that forms thin crust and wrinkles
*PILLOW LAVA *lava that erupts under water, has a round shape
*BLOCKY LAVA *cooler, lava that does not travel far from eruption, jagged when it dries.
WHY DO COMPOSITE VOLCANOES TEND TO BE EXPLOSIVE AND SHIELD VOLCANOES NON-EXPLOSIVE??1) CHEMISTRY (COMPOSITION) OF LAVA2) LAVA TEMPERATURE COMPOSITE SHIELD- Higher silica content of lavas -Lower silica content of lavasmake them more viscous (thick). make them more fluid (runny).- Lava temperatures are - Lava temperatures are quitegenerally a few hundred degrees hot, ~ 2200oF, making it easiercooler than those of shield for these lavas to “flow likevolcanoes, making the lavas water”.“thicker” in consistency.
OTHER CHARACTERISTICS ASSOCIATED WITH COMPOSITE AND SHIELD VOLCANOESBoth volcano types commonly contain abundant gases dissolved inthe magma (especially composite-type).GAS EMISSIONS:Water vapor (steam) is the most common gas emitted by a volcano(70-90%). Other common gases include; CO2, CO, SO2, SO, and avariety of other sulfurous (stinky) gases.It is the buildup of gas pressures that commonly cause compositevolcanoes to violently explode when they get “plugged up”.ASH EMISSIONS:Pyroclastic (means “hot particle”) eruptions “volcanic ash” areparticularly common with composite volcanoes and uncommon withshield volcanoes.
WHY ARE THESE TWO VOLCANO TYPES (COMPOSITE-SHIELD) SO DIFFERENT???It is most fundamentally tied to the source material from which thesetwo types of volcanoes come from, and this ties back to their tectonicsetting!!!Recall, that composite volcanoes primarily have a “continental”setting, and shield volcanoes have an “oceanic” setting.