Lava type
|
MUST have
|
Commonly has
|
Commonly lacks
|
MUST NOT have
|
|---|---|---|---|---|
| Pahoehoe | Smooth (piece-wise continuous) flow top and base Glassy upper chill crust (0.2-1.5 cm thick) Vesicular upper crust (15%-50% vesicles) Lower vesicular crust (10%-30% vesicles) |
0.3- to 80-m flow thicknesses Inflation features (e.g., tumuli) Thick dense core (0%-5% vesicles) Compound flow lobes Internal differentiation features (e.g., vesicle cylinders) |
Angular vesicles | Autobrecciation |
| Aa | Autobrecciated flow top and base Breccia clasts gnarled and spinose Subangular, microcrystalline lava Dense core Angular vesicles |
2- to 5-m flow thicknesses Clasts entrained within the core Core pushing into the flow-top breccia 5%-20% vesicularity of clasts and core Minor eolian sediment infill |
Round vesicles Inflation features Internal differentiation |
Pahoehoe surfaces |
| Slab pahoehoe | Autobrecciated flow top Slabs of broken pahoehoe surfaces |
Aa and pahoehoe clasts in breccia Thin basal breccia |
||
| Rubbly pahoehoe | Autobrecciated flow top Broken and intact pahoehoe lobes Coherent vesicular crust below breccia Lower vesicular crust |
Dense core Distorted but rounded vesicles Smooth pahoehoe base |
Basal breccia | Aa clasts |
Notes: Pahoehoe and aa characteristics from Macdonald (1953). Rubbly pahoehoe characteristics from Keszthelyi et al. (2001).