Purdue University has published an interesting Earth Impact Effects Program (Marcus, Melosh & Collins 2018). This simulator is used to calculate the size, speed and other effects of a meteorite strike (Table 1).
This is a good starting point because we have our calculated diameter of 284 km for the outer rim. Meteorite speed has been selected as 25 km/sec as ‘Asteroids strike the earth at an average speed of about 25 km/second’ (Grieve 1990).
Table 1 Data calculated using the Earth Impact Effects Simulator from Purdue University.
|
Value |
Parameter |
Comment |
|
25 km/sec |
Speed Min 17-Max 40 km/s |
(Grieve 1990) |
|
28 km |
Meteor (equivalent) Diameter |
Adjust to get 284 km Diameter |
|
284 km |
Structure Rim Diameter |
(Therriault, Grieve & Reimold 1996) |
|
8000 kg/m3 |
Meteor density |
For Iron meteorite |
|
Sedimentary |
Target rock |
Karoo and Transvaal Group |
|
5 Degrees |
Angle of approach |
Great Dyke Figs. 1b & 10c |
|
146 km |
Transient Diameter |
Earth Impact Effects Program |
|
52 km |
Transient depth |
Earth Impact Effects Program |
|
2 km |
Final depth |
Floor 15 km + melt & debris |
|
44,000 km3 |
Volume target vapourised |
Earth Impact Effects Program |
|
1068 km |
Fireball diameter |
Earth Impact Effects Program |
|
1440 more |
Radiant Energy than Sun |
Earth Impact Effects Program |
|
2.2 hours |
Duration of Radiant Energy |
Earth Impacts Effect Program |
|
11.2 |
Earthquake Richter scale |
Earth Impact Effects Program |
During impact this meteorite cluster dissipated energy equivalent of 6.86 billion Megatons of TNT (Earth Impact Effects Program). By calculation this is 180 billion times greater than the combined atomic bombs dropped on Hiroshima, 15 kt, and Nagasaki, 21 kt, (Malik 1985) and 137 million times greater than the largest man-made nuclear explosion on Earth, Russia’s Tsar Bomba 50 Megaton (Adamsky & Smirnov 1994).
The meteorite fragments shot through the crater in a few seconds causing a shock wave travelling at 5 km/second to compress the target rock. As the shock wave passed, the rock rebounded with a residual velocity of about one-fifth moving the target material at 1 km/second (Melosh 1989). This created the transient crater 146 km in diameter in just 73 seconds blasting high temperature ejecta out of the crater at ballistic speed.
Material below the fragmented meteorite was driven downwards and radially outwards (Dence 1968). As the transient crater reached maximum depth the floor came to a standstill and then started to rebound. The target floor rock was released from high pressure and, helped by gravity effects from fluid forces below, driving the crater floor upwards to a height of 29 km (Henkel & Reimold 1996).
The impacts would have vapourised 44,000 cubic kilometres of the sedimentary rock and created a fireball 1068 km in diameter. If you were standing 1000 km away, where Port Elizabeth, South Africa, is today, the Thermal Radiation, 1440 times more intense than the Sun, would have incinerated you. This was followed three and a half minutes later by a seismic shock wave, with a force of 11.2 reading on the Richter scale with the resultant earthquake damaging or flattening every single structure. The air blast would arrive 50 minutes later at the speed of sound and a pressure of 50 atmospheres which would blast away any structures left standing as well as all trees (Earth Impact Effects Program).