Geography

WHAT IS VOLCANISM

Volcanoes are generally found where

(a) Tectonic plates (b) Earth’s crust

Which ridge has examples of volcanoes caused by “divergent tcctonic plates” pulling apart?

(a)    Mid-Atlantic     Ridge                                       (b)  Pacific Ring of Fire

(c)    Both a & b                                                       (d)  None of these

Which one has examples of volcanoes causcd by ‘convergent tcctonic plate’ coming together?

(a)    Pflrifir Uim» of Fire                                          (b)  Mid-Atlantic Ridge

(c)    Both a & b                                                       (d)  None of these

Volcanoes can also form where there ts stretching of the Earth’s ——————–  and where the

________ goes thin.

(a) C rust, crust                 (b)   Plate, crust               (c)  Surface, crust (d) Plate, surfacc

 

  1. Hotspot volcanoes are caused by .

(a) Ash                                 (b) Gases                              (c) Mantle plumes (d) None

Hotspots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere.                              They may be on, near to, or far from              tectonic plate

boundaries. They arc due to hot          mantle plumes       that rise as thermal diapirs from the       core                                                            mantle

boundary and that it is not high temperature that causes the volcanism, but lithospheric extension that permits the passive rising of melt from shallow depths.

  1. Hotspot volcanoes can be found on the islands like_______________ .

(a) Indonesian                      (b) Hawaiian                     (c)   Malaysian                   (d) None of these

‘Hotspot island chains include the Hawaiian, Marquesas, Society, Pitcairn, Samoan and Galapagos archipelagos.

  1. Volcanoes are usually located on .

(a) Divergent plate boundaries                                               (b) Convergent plate boundaries

(c) Hotspots                                                                                              (d) All of the above

  1. The erupted material of volcano consists of____________ .

(a) Lava composition                                     .              (b)  Lava    texture

(c) a_&b                                                                       (d)  None  of these                  .

  1. Divergent plate boundaries after volcanic activity form_____________ .

(a)    New Seafloor            (b)   Volcanic islands       (c)   a & b                         (d) None

Divergent boundaries are characterized by a rift       in the surface of the earth along the           mid-ocean

ridges that exist in all of the major ocean basins. The ridges are composed of volcanic mountains that erupt basalt onto the surface of the ocean and by that process create new oceanic crust.

  1. A place where two plates, usually an oceanic plate and a continental plate, collide is called

(a)    Volcanic zone           (b)   Subduction zone       (c)   Continental zone       (d) None of these

  1. Magma that contains higher contents of silica is called

(a) Acid Magma (b) Basic Magma

The silica content afreets the viscosity of the magma. Basic rock (low silica content) will

produce a runny, less viscous magma, this type of magma; has the ability to flow more easily

and release pressure of a long period of time (Hawaii). Whereas Aeidie magmas contain more silica; tins causes more viscous magma.

  1. Volcanic erupted material, when inside the hill/earth/mountain, it is called and

after coming out, it is called________ .

(a)     Magma, Lava            (b)   Lava, magma            (c)   None of these

  1. The type of volcano on some moons of Jupiter, Saturn and Neptune is known

(a) Cryovolcano (ice volcanol                                   fh’i shields

(e) Cinder eone                                                          (d) None of these

A cryovolcano (colloquially known as an                 ice volcano) is,           literally,    an       icy volcano.

Cryovolcanoes form on icy moons, and possibly on other low-tcmpcrature astronomical objects. Rather than molten rock, these volcanoes erupt volalilcs such as water, ammonia or methane. Collectively referred to as cryomagma or ice-volcanic melt, these substances arc usually liquids and form plumes, but can also be in vapour form. After eruption, cryomagma condenses to a solid form when exposed to the very low surrounding temperature.

 

  1. The volcanoes formed by the alternating layers of lava and rock fragments are called

(a) Composite volcanoes                                               (b) Shields

(c) Cinder cones                                                            (d) Spatter cones

Composite volcanoes are formed by alternating layers of lava and rock fragments. This is the reason they are callcd composite. Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. When very viscous magma rises to the surface, it usually clogs the crater pipe, and gas in the crater pipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.

  1. Composite volcanoes arc also known as .

(a) Shields                                                                     (b) Stratovolcanoes

(c) Compound volcanoes                                      ‘       (d) None of these

Stratovolcanoes. also known as composite cones, are        the most picturesque     and the most   deadly

of the volcano types. Their lower slopes             arc gentle, but they rise steeply      near    the summit    to

produce an overall morphology that is concave in an upward direction. The summit area typically contains a surprisingly small summit crater. This classic stratovolcano shape is exemplified by many well-known stratovolcanoes, such as Mt. Fuji in Japan, Mt. Mayon in the Philippines, and Mt. Agua in Guatemala.

  1. Composite volcanoes usually erupt in explosive way as, when the viscous magma raises to

a surface it usually clogs_______ , so as a result______________ will increase resulting in an explosive

eruption.

(a) Crater pipe, pressure                                            (b) Pressure, cratcr pipe

(c) Mantle plume, gas                                               (d) None of these

  1. Shield volcanoes are           in size.

(a) Small                            (b)    Huge                      (c)       Medium             (d) Long

Shield volcanoes are huge in size. They are built by many layers of runny lava flows. Lava spills out of a central vent or group of vents. A broad-shaped, gently-sloping cone is formed. This is caused by the very fluid, basaltic lava which can’t be piled up into steep mounds.

  1. Shield volcanoes arc built by many layers of lava which spill out of a central vent or group of vents, so gently form sloping cones. This is caused by the fluid callcd.

(a) Basaltic lava                 (b) Runny lava               (c) Acid lava                 (d) None of these

The high temperature and low silica content allow basaltic lavas to How readily and travel far.

The Hawaiian Islands were built up from the seafloor from successive basaltic lava flows, forming large shield volcanoes. When basaltic lava erupts onto relatively flat land, flows known as flood basalts may spread out. with successive flows being piled on top of one another.

  1. Example of shield volcanoes is .

(a) Mauna loa                        (b) Kilavea                  (c) Both                        (d) None of these

Shield volcanoes arc the largest volcanoes on Earth that actually look like volcanoes. The Hawaiian shield volcanoes arc the most famous examples. Shield volcanoes are almost exclusively basalt, a type of lava that is very fluid when erupted. For this reason, these volcanoes arc not steep (you can’t pile up a fluid that easily runs downhill). Eruptions at shield volcanoes are only explosive if water somehow gets into the vent, otherwise they arc characterized by low-explosivity.

  1. Cinder cones are built from lava fragments called.

(a) Cinders                         (b)   Mantle plumes        (c) Ash                          (d) None of these

 

Cinder cones are built from lava fragments called cinders. The lava fragments arc ejected from a single vent and accumulate around the vent when they fall back to earth.

  • Cinder cone volcanoes’ example is,

‘ M Pnricufin in Mexico                                                (b) Mount Hood

(c) Hekla on Iceland                                                     M) Nolle °f *cse

  • Volcanic bombing during eruption is also called

*    (a) Pvroclasts                         <•>)   Ash                         (c)   Gases                     (d)  None of these

p QcJasts (or “tephra1) arc any volcanic fragment that was hurled through the air by volcanic livitv A pyroclastic eruption is one in which majority of activity involves fountaining or olosions A pyroclastic deposit is the resulting layer or pile of material that has fallen to the C ound by °ne or many pyroclastic eruptions. A pyroclastic rock is the hardened, solidified, or impressed version of an originally loose pyroclastic deposit.

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