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How might an asteroid form an impact feature like a Carolina bay, so unlike a conventional round crater? 

See Sandia Laboratory's recent model of what could be the long sought mechnism for Carolina Bay formation:  mulitple "Tunguska class" airbursts of smaller asteroids sending a pillars of hell onto the ground below.

INCINERATION POSSIBLE - Fine points of the "fireball" that might be expected from an asteroid exploding in Earth's atmosphere are indicated in a supercomputer simulation led by Sandia researcher Mark Boslough.

Click here for the facinating December 17, 2007 press release

INCINERATION POSSIBLE - Fine points of the "fireball" that might be expected from an asteroid exploding in Earth's atmosphere are indicated in a supercomputer simulation devised by a team led by Sandia researcher Mark Boslough. (Photo by Randy Montoya )

Movie Clips and Descriptions from the Sandia lab webpage:
The following clips are available for viewing. Apple's Quicktime is available for download from Apple's website here.

 
Asteroid Movie 4 Movie 4
 

A 62 thousand ton stationary asteroid explodes with an energy of 5 megatons at 5 km above the surface.  The movie window is 15 km wide and about 8 km high.  Bright colors of the fireball indicate temperature, ranging from steam (dull red) to rock vapor (white).  Gray background indicates air density and shows a spherical blast wave that reflects from the ground.  The fireball rises buoyantly and cools as it recedes, limiting the thermal effects on the surface.  This simulation shows what happens when momentum is ignored to simplify the problem as scientists have done in the past. The airburst is approximated by a "point source" explosion similar to a nuclear detonation. -- Sandia

 
Asteroid Movie 1 Movie 1
 

This simulation shows what happens when momentum is not ignored, an approach that is allowed with modern supercomputers and codes.  The same asteroid is now moving through the atmosphere at a typical impact velocity (20 km/s).  For illustration purposes, extra energy is deposited into the asteroid when it reaches 5 km, for a total of 5 megatons.  Momentum carries the hot fireball down to the surface, which enhances heat and wind effects on the ground.

 
Asteroid 8 Movie 8
Close-up of the previous simulation.  The box dimensions are 4 km wide and 3 km high.  The colors indicate the energy associated with vorticity, the swirling, tornado-like eddies generated by the downward motion.  High velocity winds can be sustained at ground level by vortex flow.
 
Asteroid Movie 7 Movie 7
Tracking of 5 megaton asteriod that begins exploding at 20 km above the surface, but carries its energy down to about 8 km.  Axes are labeled in cm, and colors indicate velocity in cm/s.  
 
 
Asteroid Movie 3 Movie 3
 

3D simulation of a 15 megaton explosion that is initiated 18 km above the surface, for an asteroid entering at an angle of 35 degrees above the horizontal.  Box dimensions are 40 km wide, 20 km high.  Colors indicate speed.  The hot fireball decends to the surface and slides downrange at high velocities, subjecting the landscape to blast-furnace condtions.  This did not happen at Tunguska.

 
Asteroid Movie 5 Movie 5
 

Map view of blast zone from 3-D simulation of a 15 megaton explosion.  Axes are labeled in centimeters, and colors indicate wind speed.  Expanding oblong shape is the blast wave moving along the surface, blowing down trees with wind speeds decreasing from high hurricane force of 60 m/s (magenta) to below 20 m/s (yellow).  Blast-furnace conditions are sustained downrange (left) of the origin where the fireball contacted the surface.  This did not happen at Tunguska, so the asteroid must have been smaller (less energetic).

 
Asteroid Movie 2 Movie 2
 

3D simulation of a 5 megaton explosion that is initiated 12 km above the surface, for an asteroid entering at an angle of 35 degrees above the horizontal.  Box dimensions are 40 km wide, 20 km high.  Colors indicate speed.  The hot fireball does not reach the surface, but descends to an altitude of 5 km before buoyantly rising.  At ground zero, the blast wave comes from directly above, consistent with observations of standing trees at the Tunguska epicenter.

 
Asteroid Movie 6 Movie 6
Map view of blast zone from 3-D simulation of a 5 megaton explosion.  Axes are labeled in centimeters, and colors indicate wind speed.  Expanding oblong shape is the blast wave moving along the surface, blowing down trees with wind speeds decreasing from high hurricane force of 60 m/s (magenta) to below 20 m/s (yellow).  Because the fireball stops at high altitude, there is no blast furnace zone near the epicenter and trees remain standing as observed at Tunugska.

Above descriptions from: Sandia Lab webpage

                                          

 

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