hawaiian tephra

Hawaiian IslandsHawaiian Islands

TeprhaTeprha

Source for photos and explantions on the web

• http://volcanoes.usgs.gov/Products/Pglossary/pglossary.html

Plinian Eruption Column

• TEPHRA: Any volcanic product ejected into the air.

• Includes pumice, ash, spatter and more!

Volcanic Ash

PUMICE

• Tephra may either be shot into the air ballistically or carried upwards by the convecting column and blown downwind

Eruption Column and Cloud

• Ballistically ejected particles like blocks, bombs, and spatter tend to land near the vent and build cones.

Ballistic Spatter Explosion at Night.

Notice the Parabolic Path of the Spatter.

• Convectively carried material like ash, pele’s hair, light pumice blocks, and reticulite are carried far from the vent by the ash cloud. Deposits from ash clouds get finer away from the vent.

VOLCANIC ASH

Tephra is blown by Winds

• The explosivity of a volcano is related to gas expansion and the viscosity of the magma.

• Abundant gas that expands rapidly provides the force

• Viscosity of magma is the container. If the bubbles escape easily there is little fragmentation. Trapped bubbles explode causing fragmentation.

Explosivity Index

TEPHRA: PYROCLASTIC PRODUCTS

Pyroclastic Products are Called Tephra

Tephra are named first for size, then for texture.

>64 millimeters: Bombs and Blocks (Ballistic)(includes ribbon bombs, teardrop bombs, spatter bombs, pumice bombs–blocks, lava blocks, and lithic blocks)

2 to 64 millimeters: Lapilli(includes pumice, cinder, scoria, reticulite, pele’s tears, pele’s hair, limu o Pele, accretionary lapilli, and lithic lapilli)

<2 millimeters: Ash (includes ash, pele’s hair, limu o Pele,)

• Most of the gas that drives eruptions is water that turns to steam bubbles. The water may either be inside the magma or groundwater mixed into the magma as it rises to the surface.

Hawaiian style eruptions

• Generally fairly gentle as the magma is very fluid and allows the bubbles to pass through without causing violent explosions.

Hawaiian Fire Fountain

Reticulite

Reticulite––lapilli

Reticulite Bomb

Pele’s Hair

Cinders

Cinder lapilli at Pu‘u Puai

Pele’s Tears––Lava droplets

Low Fountain and Tephra Cone––Pu‘u ‘Ō‘ō

Dome Fountain

Spatter Bombs in Flight

Spatter Deposits

Pele’s Hair From Skylight

Strombolian style eruptions

These eruptions are marked by bursts of gas that are more explosive than Hawaiian eruptions due to the greater viscosity of the magmas that keeps gas from escaping easily.

Builds cinder cones like those seen on Mauna Kea, Hualālai, Haleakala, etc.

Cinder Cone

Kohala Mountains

Cinders and Bombs

Volcanic Bomb––Mauna Kea

Small Volcanic Bombs––really lapilli!!

Pumice Bomb at Pu‘u Waa Waa

• Explosive Hawaiian eruptions that make ash are all driven by groundwater or seawater mixing with the magma.

Ballistic Spatter at Ocean Entry

Large Lithc Block in Spatter Field at Ocean Entry––

Related to Collapse of Bench and Large

Steam Explosion

Spatter and Steam Cloud

Ballistic Spatter and Steam Cloud

Limu o Pele bubble bursting

Limu o Pele

Limu O Pele

Coarse Littoral Ash from Steam Plume

Footprints in Ash

Accretionary Lapilli

Accretionary Lapilli in Keanakako`i Ash near Footprints

Diamond Head is made of ash and accretionary lapilli.

Koko Head

Pumice

Volcanic Ash––Electron Microscope Photo