What drives explosive volcanic eruptions?
Catastrophic expansion of the gas phase.
What is required for a volcanic explosion to occur?
Significant magma fragmentation and dispersal of fragments.
What is a magmatic (“dry”) explosion?
An explosion driven solely by expansion of steam bubbles.
What are the four classic eruption types in Lacroix’s (1908) classification?
Hawaiian, Strombolian, Vulcanian, and Plinian.
Which eruption type has continuous lava fountaining?
Hawaiian.
Which eruption type is characterized by pulsed bursts?
Strombolian.
Which eruption type is intermittent with violent blasts?
Vulcanian.
Which eruption type produces large continuous plumes?
Plinian.
What does the Volcanic Explosivity Index (VEI) measure?
Relative size and magnitude of explosive eruptions.
What is the scale of VEI?
0 to 8, with each step ≈ 10× increase.
What factors are used to calculate VEI?
Pyroclastic volume, column height, eruption duration, and qualitative terms.
What is tephra?
Unconsolidated pyroclasts from explosive eruptions.
What are the main size categories of tephra?
Ash, lapilli, bombs, and blocks.
What are welded tephra deposits called?
Tuff (ash tuff, lapilli tuff, tuff breccia, etc.).
What does an isopach map show?
Lines of equal tephra thickness.
What drives Hawaiian lava fountains?
Gas propelling magma upward.
Typical heights of Hawaiian fountains?
10–100 m (sometimes up to 500 m).
What clasts are typical of Hawaiian fountains?
Vesicular reticulite, Pele’s hair, fluidal ash/lapilli, and spatter.
What causes Strombolian explosions?
Single large bubbles bursting at the surface.
What is the typical gas:clot ratio in Strombolian eruptions?
10⁵:1.
Typical muzzle velocities in Strombolian eruptions?
<100 m/s.
What pyroclasts are common in Strombolian eruptions?
Lapilli to block clasts, bombs, and agglutinated spatter.
What causes Vulcanian explosions?
Vent blockage followed by sudden gas release.
Typical muzzle velocities in Vulcanian eruptions?
≤400 m/s (sometimes supersonic).
