THE NATURE OF VOLCANIC ERUPTION BY ALISHA RECONADA

THE NATURE OF VOLCANIC ERUPTION BY: ALISHA RECONADA

• Volcanic activity is commonly perceived as a process that produce picturesque, coneshaped structure that periodically erupts in a violent manner. • Some eruptions are very explosive while many others are not.

MAGMA Magma associated with an explosive eruption may be thousand of times more viscous than magma that extruded in a quiescent manner.

FACTORS AFFECTING MAGMA'S VISCOSITY • The primary factors include the magma's temperature, its composition, and the amount of dissolved gases it contains. • A magma's viscosity is directly related to its silica content. In general, the more silica in magma, the greater its viscosity. • The amount of volatiles ( gaseous components of magma, mainly water) contained in magma also affects its mobility.

WHY DO VOLCANOES ERUPT? • One of the simplest mechanisms for triggering a volcanic eruption is the arrival of a new batch of hot liquid rock into a near - surface magma reservoir. • The injection of a fresh supply of magma causes the pressure in the chamber to rise until cracks in the rock above.

WHAT IS EXTRUDED DURING ERUPTIONS? • LAVA FLOWS - because of their low silica content, hot basaltic lavas are usually very fluid • two types of lava: (1) Typical slow-moving aa flow (2) Typical pahoehoe flow

aa flow pahoehoe flow

• Lava tubes - hardened basaltic flows commonly contain tunnels that once were nearly horizontal tubes carrying lava from the volcanic vent to the flow's leading edge.

• Gases - magmas contain various dissolved gases (volatiles) held in molten rock by confining pressure, just as carbon dioxide is held in soft drinks. • The gases are about 70% water vapor, 15% carbon dioxide, 5% nitrogen, 5% sulfur, and lesser amounts of chlorine, hydrogen, and argon.

• Pyroclastic materials - when basaltic lava is extruded, dissolved gases escape quite freely and continually. • These gases propel incandescent blobs of lava to great heights.

VOLCANIC STRUCTURES AND ERUPTIVE STYLES BY: KAYCEL CASTRO

ANATOMY OF A VOLCANO Fissure § A crack that develops in the crust from which magma moves A close- up of a crack in the volcanic surface of a cooled lava flow from the crater of Mt. St. Helens

ANATOMY OF A VOLCANO Conduit/ pipe § A circular path where magma localizes

ANATOMY OF A VOLCANO Vent § Surface opening Fumarole § A vent that only emits gases

ANATOMY OF A VOLCANO Crater § Funnel- shaped depression at the summit

ANATOMY OF A VOLCANO Parasitic cone § Produced from continuous eruption from the fissures in the base

SHIELD VOLCANOES §Shape resembles a warriors shield §Produced by accumulation of basaltic lava §Have grown up from the deep ocean floor to form islands §Example: Islands of Hawaiian chain, Iceland, Galapagos

Mauna Loa: Earth’s Largest volcano • Base to summit: 9 km high • Volume: 40 000 cubic km • Caldera: 2. 6 x 4. 5 km, 150 m depth

Kilauea, Hawaii: Eruption of a Shield volcano § Most active shield volcano (50 eruptions) § “curtain of fire” in 1983 § Cinder and spatter cone: Puu Oo

CINDER CONES §Composed of loose pyroclastics §Most abundant of the major types of volcanoes §Have a high angle of repose and large, deep craters §very short eruptive cycles § 95% formed in less than one year

Paricutin: Life cycle of a Cinder cone § First eruptive phase: 1943 in a cornfield §June 1944 Aa flow covered the San Juan Parangaricutiro §Today, it will not erupt again

COMPOSITE CONES §Most picturesque but potentially dangerous volcanoes §Also called stratovolcanoes §The Ring of fire §Large, nearly symmetrical structure §Product of gas- rich magma, andesitic composition

Nuée Ardente: A Deadly Pyroclastic Flow §Glowing avalanches §Hot gases with ash and large rock fragment §The destruction of St. Pierre §Eruption of Mount Pelée 1902 § 28 000 inhabitants died

Lahars: Mudflows on Active and Inactive Cones §volcanic debris becomes saturated §when snow melt during eruptions §volcanic deposits triggered by rainfall

CALDERAS §Caldaria= cooking pot §Large, collapse depressions having a circular form § 1 - 10 km in diameter § 3 types depending on formation: § Crater lake- type calderas § Hawaiian type calderas §Yellowstone- type calderas

Crater lake- type Calderas §Crater lake, Oregon §Collapse of the summit of a composite volcano caused by eruption §Eruption of Mount Mazama § Wizard Island §Maximum diameter: 10 km, 1175 m deep

Hawaiian type Calderas §Collapse of a shield volcano caused by subterranean drainage from a magma chamber §Hawaii’s active shield volcano, Kilauea §Large caldera that measures 3. 3 x 4. 4 km § Vertical walls, looks like a deep, flat bottomed pit

Yellowstone type Calderas §Collapse of a large area caused by extraordinary volume of erupted material §Produce the largest volcanic structures on earth §Yellowstone National Park § 100 cubic km of pyroclastic material erupted, 70 km across

FISSURE ERUPTIONS AND LAVA PLATEAUS §Columbia plateau §Basaltic lava buried the existing landscape (50 m thick)

§COLUMBIA PLATEAU

VOLCANIC PIPES AND NECKS §Pipes- “Windows into the earth” §Necks- remains after the cone has vanished §Ship Rock, New Mexico