Volcanoes and Magma Composition

• Volcanoes are elements of the landscape formed by magma.
• Magma rises through fractures in the Earth's crust and erupts as lava or a mixture of gas, ash, and volcanic fragments.
• The accumulation of erupted materials forms a volcanic edifice.
• An edifice's appearance is determined by the chemical and physical characteristics of the emitted materials and the feeding system.

Magma Sources and Types

• Magma mainly originates from the upper mantle.
• Rocks can also melt in deeper parts of the crust.
• Primary magma melts at depths over 35 km, thus, in the mantle itself.
• Secondary magma melts closer to the crust, is richer in silica, denser, and more viscous.
• Molten material is called lava after its eruption onto the surface

Volcano Types

• Solidified lava accumulates to form a volcanic edifice
• Volcanoes are split into central and linear types

Central Volcanoes

• Mount Etna and Vesuvius are central volcanoes

Linear Volcanoes

• Oceanic ridges are where linear volcanoes normally occur

Cone Shaped Volcano

• Cone-shaped volcanoes with steep sides form when magma rises along a central conduit.
• Alternating lava and ash layers create steep-sided stratovolcanoes.
• Examples are Stromboli, Vesuvius, Etna, Fujiyama, and Majon.
• Pointed shapes are caused by lava is rich in silica

Acid Magma

• Magma containing over 60% silica is acid magma, is viscous, and flows slowly.
• Acid Magma struggles to ascend the volcanic chimney, hindering material and gas escape.

Basaltic Lava

• Lavas with basaltic content are hot, low in silica and produce low-angle shield volcanoes like those in Hawaii.
• The ascent of magma along fracture systems creates elongated surface structures.
• Violent eruptions can form craters ranging from tens to hundreds of meters in diameter.

Caldera

• Calderas can be large circular depressions, that destroy pre-existing volcanic structures

Eruptive Behavior factors

• Eruptive behavior depends on chemical composition and gas content.
• Gas-rich basic magmas cause lava flows and fountains, while acidic magmas cause large eruptions.
• Degassed magmas can produce quiet lava effusions, or viscous bodies.

Lava Flows

• The fluid products of volcanic eruptions are called lava.
• Lavas varies in chemical makeup, gas composition, and temperature.
• These factors affect magma flow, which is essentially viscosity
• The appearance of lava flow depends on composition, viscosity, gas content and morphology of the ground

Pyroclasts

• Pyroclasts are the solid particles that are ejected from a volcano.
• The three types include:
  • Volcanic Ash
  • Lapilli
  • Volcanic Bombs

Volcano Locations

• Active volcanoes are located both on land and on the ocean floor.
• Most volcanic activity occurs at oceanic ridges, where basaltic lava flows.
• Most of Earth's emerged volcanoes are at continent margins, or volcanic island chains.

Hot Spots

• Isolated volcanoes within plates are called hot spots.
• Hot spots form basaltic lava cones, which differ from ridge formations and are rich in alkaline metals.
• About 40 hot spots are located within the African and Pacific plates.

Hot Spot locations

• Located far from plate margins, such as Hawaii.
• Situated near divergent margins, with high volcanic activity, like Iceland.
• Hot spots are believed to originate from plumes or cylindrical currents from the deep areas of the mantle, explain chemical composition of the magma.
• Plumes cause partial melting in superficial areas when they reach the lithosphere's base, the created magma rises through the lithosphere to the surface

Subaerial Volcanoes

• A row of subaerial volcanoes forming islands is produced when a plate moves over a hot spot.
• Islands are dragged along when the plate moves, distant islands become extinct volcanoes.
• Structures are less elevated and submerge underwater becoming guyots.
• Guyots are reliefs with a flattened top.

Shield Volcanoes

• Largest volcanoes, consisting of large volcanic structures with moderate sloping sides.
• Shield volcanoes originate from flowing of flowing lavas and contain small quantities of gases, are not violent.

Stratus Volcanoes

• Cone-shaped volcanoes with very steep sides.
• Stratus volcanoes consists of alternating lava flow and pyroclastic material layers from explosive eruptions.
• Solidifying lava obstructs the volcanic conduit, the accumulated pressure may remove the plug.

Calderas and Cinder Cones

• Structures derived from volcanic action

Calderas described

• Large circular depressions formed by a collapse

Cinder Cones described

• Regular masses of solidified lava fragments that have deep craters.

Mechanism of Magma

• Volcanism is the ascension of molten rock from the Earth's inner layers, mixed with gases at great temperatures and pressure, known as magma.
• Magma becomes lava when the gases dissipate, once the magma is in the volcanic crater, it rapidly solidifies, and disperses.
• Temperature and pressure in strata between 60 and 70 km deep enable partial rock melting.
• Magma rises through the upper mantle to the crust, where it forms a magma chamber.
• Eruptions occur vertically or horizontally out of the magma chamber.

Terrestrial Volcanoes

• Terrestrial volcanoes have magma chambers linked to upper mantle that give rise to volcanoes.
• A volcanic chimney connects the chamber outside, through a central vent, and some lateral vents.
• A large mouth is called a crater.
• Volcanic edifice determined by type of lava.

Classifying Eruptions

• They are classified based on these characteristics:
  • Hawaiian
  • Icelandic
  • Strombolian
  • Vulcan
  • Plinian

Understanding Volcano Behavior

• Phenomena is observed through general behavior, cyclical events, magma composition analysis.

Hawaiian Eruption

• A type of eruption that does not explode, has fluid and hot lava.
• The magma comes directly from the Earth's mantle, a hotspot can occur here
• Gentle sloping sides.
• Lava is very fluid , so travels for miles without cooling
• It is the least dangerous with water to lava interaction being the only risk.
• Hawaiian volcanoes such as Kilauea and Mauna Loa share its name

Icelandic Eruption

• Occur from linear volcanoes, not cone-shaped, with long, parallel fractures where lava flows from.
• These volcanoes erupt volcanic magma along ocean ridges, like in Iceland.
• Eruptive fissures disappear after eruptions because they are covered in lava, they reappear later.
• Numerous lava flows can create the Bardarbunga volcano

Strombolian Eruption

• It takes its name from he Stromboli volcano's eruptions.
• Viscous basaltic magmas triggers the ejection of fountains and shreds of lava at regular times.
• Large volcanic bombs can be produced

Vulcanian Eruption

• Named after Aeolian archipelago island of Vulcano.
• It is a very hazardous event where lava bombs and clouds of gas filled cloud of ash are emitted.
• Magma is basically acidic
• Eruptive fractures, crater rupture, and lateral vents are also possible

Plinian Eruption

• Originate from stratovolcanoes.
• Pliny the Younger defined/observed the Eruption of Vesuvius in 79 AD.
• These eruptions occur violently due to the high viscosity.
• Fiery clouds happen often as well as partial and complete volcanic explosions
• Ultra-Plinian eruptions, or Krakatoian eruptions, destroy the volcano edifice.
• Pelean-type volcanoes erupt laterally.

Classifying the Type of Lava Flow

• Effusive, effusive-explosive, or explosive

Effusive

• Generally related to hotspots, magma is fluid.

Explosive

• Viscous magmas may not form a lava flow, but a plug that may collapse in entirety, causes and eruptive column of lapilli to rise above volcano.

Effusive-Explosive:

• Consists of half of material

Lahars

• Lahars are mudflows that form when ash mixes with rainwater along slopes of a volcano
• Intense rain can also cause them due to water vapour being emitted from the volcano

Secondary Vulcanism

• Associated with volcanic action, with the manifestations occuring while a volcano is quiecent
• It is the only indication of magma existence in volcanically active areas, for example gas emission

Fumaroles

• The emissions of mostly water vapor, accompanied by carbon dioxide and other gases are called this.
• They emit pure steam inside stoves, caverns and crevasses

Solfatares

• The emissions are hot and gaseous (sulfur compounds, hydrogen), the solfataras of Pozzuoli are well known in Italy

Geysers

• Boing water and steam are violently emitted from the ground.
• They happen when the water comes into contact with the Earth's superheated rocks
• The lithostatic pressure lowers and it transforms to steam, causing violent emissions

Explore the factors shaping volcanoes, including magma composition, silica content, and viscosity. Understand the differences between magma types and their impact on volcanic structures. Learn about magma chambers, lava flows, and eruption styles.