Feature of Lava

1. SIMPLE AND COMPOUND LAVA
FLOW
Effusion rate: rate of discharge, measured in
cubic meters per second
 Basaltic lavas extruded at relatively low
effusion rates produce compound lava flow
 Basalt lavas with higher effusion rates
produce extensive flows. These flows are
composed of a single cooling unit and are
called simple flows.

3. JOINTING CHARECTERISTICS
 thicker simple flows exhibit a three-tiered
character
From bottom to top:
 1- lower colonade
 2- a middle entablature
 3- an upper colonade

4. LOWER COLONADE
 composed of columnar joints
develop perpendicular to the cooling
surface
 vary in length from one to five meters
Diameters less than 1 m
 column is polygonal in cross-section
(typically hexagonal) and bounded by 4-to-8
joints

6. ENTABLATURE
 entablature is composed of an array of
closely spaced subvertical joints.

7. LAVA CHANNELS
Fluid basalt can move down slope by
creating its own channelways or by flowing
down in pre-existing stream channels

8. LAVA LEVEES
Pahoehoe flows: natural levees constructed
as channel overflows
 a'a flows: levee build up occur by the
bulldozing effect of the moving lava.

9. LAVA LAKES AND LAVA FALLS
Lava can accumulate in volcanic craters,
filling the craters to a high level to
generate lava lakes.
When lava lakes overflows, it creats lava
falls

10. TUMULI
elliptical domed structures. 2 to 10 meters
high
 develops when slow-moving lava beneath a
solidified crust wells upward.
 best developed on the surface of flows that
are ponded in depressions, like craters or
calderas.
Featured by central crack along the length
of the tumulus.

12. ROOTLESS ERUPTIONS
 result from surface eruptions on pahoehoe
surfaces
 When the pahoehoe crust thickens and the
underlying lava becomes cool, viscous, and
gas-depleted, pasty lava can squeeze up
through the axial fracture of the tumulus

13. LAVA TUBES
The chilling and crystallization of basaltic
lava around the sides, bottom, and top of
lava channels produces a rock-encased
conduit called a lava tube
 surrounding basalt crystallizes and
insulates interior lava
 efficient mechanism for basaltic lava flows
to travel great distances

15. LAVA AND WATER
The injection of basaltic lava into surface
water can be highly explosive
 Pahoehoe tends to pour into water in a
passive manner
More explosive interactions are generally
associated with a'a flows

17. PILLOW BASALTS
Formed due to passive interaction
 These are bulbous bodies with quenched,
glassy appearance.
often spherical, with diameters of 30-100
cm

18. HYALOCLASTITE
Quenching and fragmentation of basaltic
lavas produces an accumulation of angular,
glassy fragments called hyaloclastite.

19. HYDROVOLCANIC ERUPTIONS
 generated by the intereaction of magma
with either groundwater or surface wate.
 Also known as Surtseyan

20. Hydrovolcanic eruption at
Ukinrek, Alaska (1977)