L7: volcanoes and earth resources

volcanoes

geological hazards that can destroy life on Earth. however they are windows in which we can see the interior of the Earth to understand the plate tectonic process and mantle convection. they affect the atmosphere and hydrosphere. they are also sources of mineral resources and energy.

what is a volcano?

hill or mountain constructed from the accumulation of lava and other erupted materials.

volcano anatomy

magma transcends because it has a lower density than the surrounding rock. it originates in the asthenosphere rises through the lithosphere. to form a crustal magma chamber. lavas erupts through a central vent and side vents

why do volcanos form?

• mid ocean ridge

• where plates collide

• hotspots (a fixed spot)

magma (gases)

as magma rises it begins to degas and reduces density. lower pressures equals more degassing and rises faster. the more water in the melt the more vapour that will form.

types of eruptions

• effusive eruptions

  • hotspots are basaltic so they will be effusive (more fluid)

• explosive eruptions

  • melts rich in silica will be explosive

  • high silica environments are only found in locations where oceanic plate collides with continental crust

*controlled by magma viscosity and gas and composition of melt

basaltic lavas

• high temperature (1000 - 1200C)

• low in silica

• high in iron, magnesium, and calcium

• extremely fluid (travel up to 200km/hr)

• produce ultramafic rocks

• product of mantle melting

• most common magma type

• produce ropy lava

• Aa patterns

• pillow lavas (cooled underwater)

• columnar basalt

  • slow cooling may allow gas to escape which can lead to columnar jointing at surface owing to contraction

andesitic lavas

• intermediate silica content

• mostly produced on subduction zone (e.g. Andes)

• more silica than basalt (lower temp and flow slower)

• (e.g. Mount St Helen)

phreatic explosions

hot, gas-charged magma encounters groundwater or seawater producing superheated steam

rhyolitic lavas

• granitic lavas

• silica content > 68% with lots of Na and K too

• lowest temperature (600-800C)

• they move slowly

• contain more gases

texture of volcanic rocks

provides information about the conditions under which they solidified. coarser-grained textures with visible crystals means that the lavas cool slowly. abundance of cavities and vesicles indicates lots of water vapor and gases.

pyroclastic deposits

lava and any overlying solid rock material sent into the air during an explosion including ash, lava bombs, and pyroclastic flows (hot ash and gases cloud).

eruption styles and landforms

if the eruption produces lots of fluids (basaltic) the landscape will be more flat. more viscous magma will form cones.

volcano types

Eastern Australian hotspot volcanism

a belt of recent volcanism occurs down the eastern states starting in far north-Queensland and stretching down to vic-south aus coastline. the only ‘Australian’ active volcano is on heard island.

categorising activity

• active

• dormant

• extinct

volcanism and hydrosphere

volcanic activity does not stop when lavas cease to flow. groundwater enters in contact with hot buried magma which creates fumaroles and geysers. the entire volume of ocean’s water is circulated through the cracks and cents on spreading centres. gases that come to the surface may mobilise metals such as copper, silver, cobalt, nickel, and manganese. this is because the water from the ocean is circulating through these rocks so they metals will dissolve and precipitate nearby the vents. extremophiles live here too (acidophiles, thermophiles, barophiles, Metallophilic organisms)

volcanoes and climate

volcanoes release water vapor (70-95%) as well as gases such as CO2, SO2 which can form aerosols, and Cl which destroys the ozone. surface cooling and acid rains are effects. dust from volcanoes can travel very long distances.

Large Igenous Provinces (LIP)

fissure eruption on continents and oceans. they release immense amounts of lava in short periods (1 Ma). basaltic magma is not related to normal sea spreading it is associated with hotspots.

volcanoes and mass extinctions

there is an association between volcano eruptions and mass extinctions.

volcanoes and humans

• 600 million people live close to active volcanoes

• repeat of a large eruption recorded on geological record could destroy civilisation

• people mainly die due to tsunamis, pyroclastic flows, direct lahars and indirect effects such as famine

volcano soils for industrial materials and energy

volcanic soils are mineral-rich soils that create fertile conditions for agriculture, we can derive building material from these sources such as hydrothermal vents and ore deposits.

why are natural resources important?

they provide all things we need to survive including food, water, air, and shelter. they include renewable resources (e.g. plants) and non-renewable resources (e.g. fossil fuels and minerals)

example: smart phones and toothpaste

urbanisation

urbanisation is a growth force for mining activities

green energy

green energy from renewable resources still requires massive amounts of mineral resources (e.g. electrical vehicles). we also need to build new facilities for new sources of energy.

fossil fuels (hydrocarbons)

fossils fuels are fuels produced from the remains of ancient plants and animals. they include coal, petroleum (oil) and natural gas.

oil

oil is produced from rocks in water that contain dead plankton which accumulate in layers at the bottom of the ocean. overtime these layers will decay, the temperature will drop and pressure will turn in into kerogen. depending on the depth kerogen will become gas or oil in reservoirs. they use seismic imaging to detect where oil is.

coal

coal is formed in swamps because it requires decaying vegetation, mixed with clays. increased compaction of layering increases the energy we can extract from the resource. we need coal to make steel. we can use tires to replace coal even though we do not have enough tires. compressed drives off volitiles, low cellulose.

how do we extract metals?

to extract metals we need to mine a rock that contains those minerals. rocks that contain metals that have economic value are called ore.

ore and gangue minerals

ore is a metalliferous mineral that may be extracted profitably from an orebody

gangue minerals: those minerals that form part of the ore body but do not contribute to the economically extractable part of the deposit

most ore minerals of metals are not native metals, but are compounds in which the metals are bonded and from which they must be extracted. waste rock (gangue rock) which has its precious minerals extracted can be an environmental hazard (sulphide leeching).

how would we concentrate metals in nature?

the igneous process where some metals will combine for minerals (magmatic deposits) or hydrothermal deposits

volcanogenic massive sulphide deposits

hot water dissolving minerals released into water

supergene environment

where groundwater leeched ore minerals from a rock and moves them to another location where they precipitate

residual mineral deposits

the formation of mineral deposits by intense weathering and leaching

indrustrial minerals

naturally occurring rocks or minerals that are of economic value, other than metallic ores and mineral fuels. such as limestones, clays, sand, gravel, diatomite, kaolin, bentonite, silica, barite, gypsum, and talc.

some examples of applications for industrial minerals are construction, ceramics, paints, electronics, filtration, plastics, glass, detergents and paper