Hydrovolcanic Explosions

The August 27, 1883 Krakatoa hydrovolcanic explosion was modeled using the NOBEL code in references 1 and 19. 

A hydrovolcanic explosion is generated by the interaction of hot magma with ground water. It is called Surtseyan after the 1963 explosive eruption off Iceland. The water flashes to steam and expands explosively. Liquid water becoming water gas at constant volume generates a pressure of 30,000 atmospheres. 

The water in the hydrovolcanic explosion was described as liquid water heated by the magma to 1100 degrees Kelvin or 19 kcal/mole. The high temperature water is an explosive with the hot liquid water going to a water gas. The BKW steady state detonation state has a peak pressure of 89 kilobars, a propagation velocity of 5900 meters/second and the water is compressed to 1.33 grams/cc. 

Krakatoa was modeled in two dimensions as a spherical island 200 meters high above the ocean level and 3 kilometers in radius tapering down to ocean level by 4 kilometers. The ocean was 100 meters deep and extended in the rock under the island. The lava was initially assumed to interact with the water in the center of the island in a 500 meter radius hot spot region. The propagating hydrovolcanic explosion propagated outward at about 5900 meters per second and at a constant volume pressue of about 30,000 atmospheres. 

A fully compressible reactive hydrodynamic model for the process of hydrovolcanic explosion of liquid water to steam at constant volume and pressures of 30,000 atmospheres has been applied to the explosion of Krakatoa in 1883. The idealized spherical geometry exhibits the general characteristics observed including the destruction of the island and the projection of the island into high velocity projectiles that travel into the high upper atmosphere above 2 kilometers. A high wall of water is formed that is initially higher than 100 meters driven by the shocked water, basalt and air. 

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The expansion of the hydrovolcanic explosion is shown in Figure 6.60 at various times up to 10 seconds as density picture plots. 

Figure 6.60 The NOBEL density profiles for the model of the Krakatoa hydrovolcanic explosion.

The water wave profiles at 4, 5, and 8 kilometers are shown in Figure 6.62. The wave outside the hydrovolcanic explosion at 4 km is 130 meters high and decays to 48 meters by 5 kilometers and to 7.5 meters at 8 kilometers. 

The states of the water at 1.5 kilometers in the middle of the hydrovolcanic explosion of the water reached pressures greater than 25,000 bars and expanded to altitudes greater than 2 kilometers and drove the Krakatoa island basalt to altitudes greater than 2 kilometers. Perhaps the hydrovolcanic explosion looked something like the 1946 Bikini nuclear explosion shown in Figure 6.63 without the warships. The Baker shot was a 21 kiloton device fired at 27 meter depth in the ocean. The Krakatoa event released 150 to 200 megatons. 

The NOBEL modeling of hydrovolcanic explosions and movies of the process are on the CD-ROM in the /NOBEL/KRAKATOA directory and are included in the KRAK.PPT PowerPoint. 

CONE - Explosive Cones KRAKATOA - Hydrovolcanic Explosions... 

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