How many volcanoes erupted during the historic time and active?
550
A volcano that hasn't erupted during the historic time
Dormant volcanoe
Volcano emissions, surface development and oceanic crust are:
Constructive process
A good reason to study volcamism?
Illustrates the complex interactions among earth systems and has impact on the atmosphere
What is a volcano?
Hill or mountain that forms around the vent
Volcanism accounts for what?
Volcanic (extrusive igneous) rocks
Lava differences?
Chemical composition,gas content, and temperature
The higher the silica in lava?
The lower temperature and the more viscous
More gas in lava?
More violent
Types of lava?
Basaltic, Andesitic, Rhyolitic
Basaltic lava are:
High temperature and low silica content, is extremely fluid
Pahoehoe vs. Aa
Single basaltic ropy flow
Andesitic lava are:
Lower temp., higher silica; gases can build up beneath the plug & eventually blow off the top of volcano
Rhyolitic lava are:
They are stickiest; most explosive volcanic eruptions
What do all volcanoes have
Plumbing system and most have crater; but each volcano is unique
What are Shield volcanoes called:
They are laying on the ground convex side up like a shield; almost runny flow of basaltic lava
Stratovolcanoes are made of:
Alternation of intermediate (andesite) lava flows and pyroclastic materials
Stratovolcanoes flwo composition is:
Rather andesitic (intermediate, thus more viscous
Calderas cannot support the roof and can:
Collapse catastrophically
Volcanic Hazards
Significant natural hazard to the society, kill people,damage properties
Type of Volcanic Hazards
Lahars, Flank collapse, Eruption clouds, Caldera collapse
Igneous rocks form when?
Molten rock cools to a solid state
What is Magma?
Molten material below the earth's surface
Magma is under?
Intense pressure and tends to rise/squeeze along fractures and zones of weakness
What are Intrusions?
Bodies of magma that pushes it way into crust
What are Extrusions?
Lava when it spills at the surface
Igneous rocks that are Glassy texture
very fast cooling
Igneous rocks that are Aphanitic texture
Made of crystal too small to see <1mm; fast cooling; Basalt
Igneous rocks that are Phaneritic texture
Visiable crystal, 1-10mm; slow cooling magma; Granite
Igneous rocks that are Pegmatitic texture
large grans >1cm
Igneous rocks that are Porphyric texture
2 distinct sizes of crystals
Igneous rocks that are Vesicular texture
Holes left by the gas escaping; Pumice, Scoria
Extrusive igneous rocks are:
Magma erupts at the surface in the form of lava; fine grained texture
Intrusive igneous rocks are:
Molten rock intrudes into rock masses; coarse-grained texture
8 rock-forming minerals comprise most of igneous rocks:
Quartz, plagioclase,feldspar, mica,amphibole, pyroxene, muscovite, olivine
Felsic rocks are:
Light colored igneous rocks; mainly clear mineral; such quartz
Mafic rocks are
Dark igneous rocks poor in silica content rich in magnesium and iron
What is the coloe index?
% by volume of mafic crystals in rock
Sediments are defined?
Product of the weathering of preexisting rocks
Sedimentary rocks belong to a class?
Form at the earth surface by surface processes
Importance of sedimentary rocks?
Host many natural resources such as oil, gas, coal, uranium
Sediments come from alteration of preexisting rock process...
Weathering
Fragmented by mechanical processes; e.g., action of plant roots on rocks, frost wedging...
Physical weathering
Minerals in the rock are altered or dissolved; e.g.,rusting of iron, dissolution of rocks by acidic solutions
Chemical weathering
Different agents of _____ are streams, wind, glaciers and gravity
Erosion
Occurs when currents of wind and water, ice glaciers downhill
Transportation
Strong current (>50 Cm/s)
Carry gravel
Moderately strong current (20-50 Cm/s)
Lay down sand
Weak currents (<20 Cm/s)
Carry mud; velocity sorting; abrasion
Erosion agent dies
Depostion
Sediments into sedimentary rock
Lithification
Sediments under their weight
Compaction
Gluing the loose sediments
Cementation
Made up of solid particles
Detrial or siliciclastic sedimentary rocks
During the chemical weathering several compounds and ions dissolve in water
Chemical sedimentary rocks; precipitate to yield evaporites
Form near the environment of deposition from precipitated minerals mixed with remains of organisms
Bioclastic sedimentary rocks
Distinct layers separated from one another by surfaces above and below
Strata or beds
Layers are arranged at an angle to the surface on which they are deposited
Cross-bedding
Small ridges appearing in some sand deposits
Ripple marks
Clay-rich sediment dries and shows intersection fractures
Mud cracks
Few centimeters thick and is composed of organic matter
Horizon O
Also called topsoil
Horizon A
Also called subsoil
Horizon B
Partially altered bedrock with little or no organic matter; will define whether the soil will be acidic or base
Horizon C
Called Bedrock
Horizon R
Changes in their texture and mineral compistion
High temperatures and pressures cause
Is one of these processes that can eventually bring rock material deep enough in crust
Subduction of lithospheric plates; result is large class of rocks called metamorphic rocks
Metamorphic rocks from the work?
Greec "change rocks
During metamorphism...
submitted to sufficient heat, pressure, and fluids activity; mineral compostion change, texture or both
Three principal agents:
Heat, pressure, and fluid activity
Reaction involving silicates compounds are
metamorphism is a very slow process
Role of heat
agent of metamorphism; bonds between atoms & molecules in mineral crystals are broken; source of heat is usally provided a nearby magmatic intrusion
Area closer to the intrusion are the most effected...
when rocks are intruded by bodies of magma
Temperature increase with depth according to a
Geothermal gradient(25-30 C/km in avg.
Role of pressure
Confined pressure allied equally and directed pressure
Role of Hydrothermal Fluids
When the rock is submitted to the lithostatic pressure, it is squeezed, and fluids are liberated
Metallic ions come in contact with
Surrounding rocks and are eventually traded with the elements in these rock; metasomatism
Contact metamorphism take place where?
Body of magma intrudes in the crust
What is the degree of metamorphism depend on?
Distance from the intruding body and closer higher heat.
Regional metomorphism
A large area & usually caused by tremendous temp. pressure and deformation; convergent plate boundaries
Chemical reactions between the seawater and the rock forming altered basalt
Seafloor metamorphism; also call metasomatism
The high speed and the violence of the impact bring heat and pressure
Shock metamorphism
Located where subsidence is active
Burial metamorphism
Metamorphic rocks usually exhibit two main types of textures
A: Foliated metamorphic rocks; B: Non-foliated metamorphic rocks
Foliated metamorphic rocks; heat and pressure minerals arranged in parallel
Slate -> Phyllite -> Schist -> Gneiss
Non-foliated metamorphic rocks
Mosaic of roughly equidimentional minerals; do not exhibit elongated platy minerals
When Non-foliated metamorphic rocks are made of mainly one mineral
Granoblastic; e.g. Marble, and quartzite