Volcanic products (1)

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 .

2. 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

3. 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

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

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

6. 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.

7. 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

8. 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.

9. 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

10. 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

11. 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

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

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

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

15.   Hydrovolcanic eruption at Ukinrek , Alaska (1977)