This document defines and describes different types of tephra or volcanic ejecta produced during eruptions, including ash, lapilli, blocks, bombs, pumice, scoria, and their resulting deposits. It also discusses volcanic phenomena associated with tephra such as pyroclastic flows, lahars, and the hazards posed by lahars.

1. • Tephra (Greek, for ash) is a generic term for any airborne
pyroclastic accumulation.
• Individual eruptive fragments are called pyroclasts ("fire
fragments").

2. 1) ASH :-
• Very fine-grained fragments (< 2 mm).
• Dominated by broken glass shards.

3. 2) LAPILLI :-
• Pea- to walnut-size pyroclasts (2 to 64 mm).
• Often look like cinders.
• Rounded spheres known as accretionary lapilli are
formed in water rich eruptions.

4. 3) BLOCKS AND BOMBS :-
• Fragments >64 mm.
• Blocks are ejected as solid fragments with angular shapes.

5. • PELE'S TEARS :- Lapilli-size fragments of basaltic lava may cool
quickly while airborne, to form glassy teardrop-shaped lapilli
called Pele's tears.
• PELE’S HAIR :- During strong winds, the molten fragments that
can be drawn out into fine filaments are called Pele's hair.
• SPATTER :- They are lapilli- to bomb-size fragments produced
by Non-explosive Hawaiian-type eruptions.

6. • PUMICE :- They are produced from vigorous gas
escape in felsic lavas.
• RETICULITE :- They are produced from similar
gas escape in mafic lava.
• SCORIA :- A denser mafic rock containing a
smaller abundance of relatively large vesicles.

7. • Scoria-fall deposits :- These are derived from Strombolian
eruptions of scoria cones. The deposit is composed of basaltic
to andesitic vesiculated pyroclasts (scoria) lying near the
eruptive vent.
• Pumice-fall deposits :- These are derived from Plinian
eruptions of stratovolcanoes. The deposit is composed of
highly vesiculated dacitic to rhyolitic pyroclasts (pumice)
which can be distributed for hundreds of square kilometers
away from the vent.

8. • Ash tuff - rock dominated by ash; sometimes
simply referred to as tuff.
• Lapilli tuff - rock dominated by lapilli.
• Tuff breccia - rock containing 25% to 75% blocks
and/or bombs.
• Pyroclastic breccia - rock containing at least 75%
blocks and bombs.
• Agglomerate - rock containing at least 75%
bombs.
• Agglutinate - rock composed of fused, largely
unrecognizable, basalt spatter fragments.

9. • Fluidized mixture of solid to semi-solid fragments and hot,
expanding gases that flows down the flank of a volcanic
edifice.
• Heavier-than-air emulsions that move much like a snow
avalanche.
• Most deadly of all volcanic phenomena.

11. • Indonesian term for a volcanic mudflow.
• Lethal mixtures of water and tephra have the consistency of
wet concrete.
• Maximum temperature of a lahar is 100 degrees Centigrade.

13. • Majority are produced by intense rainfall during or after an
eruption.
• A tragic example of such an event was the 1991 eruption of Mt.
Pinatubo in the Philippines. An estimated 700 people died from
burial by the ensuing lahars, together with the collapse of
structures beneath the wet ash.

14. • Lahars can destroy anything by direct impact.
• Lahars can lead to increased deposition of sediment.
• Lahars can block tributary streams.
• Lahars can bury valleys and communities with debris.