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.

JOINTING CHARECTERISTICS thicker simple flows exhibit a three-tiered

characterFrom bottom to top: 1- lower colonade 2- a middle entablature 3- an upper colonade

LOWER COLONADE composed of columnar jointsdevelop perpendicular to the cooling

surface vary in length from one to five metersDiameters less than 1 m column is polygonal in cross-section

(typically hexagonal) and bounded by 4-to-8 joints

ENTABLATURE entablature is composed of an array of

closely spaced subvertical joints.

LAVA CHANNELSFluid basalt can move down slope by

creating its own channelways or by flowing down in pre-existing stream channels

LAVA LEVEESPahoehoe flows: natural levees constructed

as channel overflows

a'a flows: levee build up occur by the bulldozing effect of the moving lava.

LAVA LAKES AND LAVA FALLSLava can accumulate in volcanic craters,

filling the craters to a high level to generate lava lakes.

When lava lakes overflows, it creats lava falls

TUMULIelliptical 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.

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

LAVA TUBESThe 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

LAVA AND WATERThe injection of basaltic lava into surface

water can be highly explosive Pahoehoe tends to pour into water in a

passive mannerMore explosive interactions are generally

associated with a'a flows

PILLOW BASALTS

Formed due to passive interaction These are bulbous bodies with quenched,

glassy appearance.often spherical, with diameters of 30-100

cm

HYALOCLASTITEQuenching and fragmentation of basaltic

lavas produces an accumulation of angular, glassy fragments called hyaloclastite.

HYDROVOLCANIC ERUPTIONS generated by the intereaction of magma

with either groundwater or surface wate. Also known as Surtseyan

Hydrovolcanic eruption atUkinrek, Alaska (1977)