The good people of Arizona university has developed an Earth Impact Effects Program, which basicly calculated what happens if something big and fast hit Earth. This is very fun to work with, if for instance we place our self 10km for the impact point of a 1km big iron comet, we get this result:
Projectile Diameter: 1000.00 m = 3280.00 ft = 0.62 miles
Projectile Density: 8000 kg/m3
Impact Velocity: 51.00 km/s = 31.67 miles/s
Impact Angle: 45 degrees
Target Density: 2750 kg/m3
Target Type: Crystalline Rock
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 5.6 x 106years
The projectile begins to breakup at an altitude of 31800 meters = 104000 ft
The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 50.8 km/s = 31.6 miles/s
The impact energy is 5.41 x 1021 Joules = 1.29 x 106MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension 1.54 km by 1.09 km
Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the Earth’s rotation period or the tilt of its axis.
The impact does not shift the Earth’s orbit noticeably.
Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
Transient Crater Diameter: 23 km = 14.3 miles
Transient Crater Depth: 8.14 km = 5.05 miles
Final Crater Diameter: 34.8 km = 21.6 miles
Final Crater Depth: 0.861 km = 0.535 miles
The crater formed is a complex crater.
The volume of the target melted or vaporized is 48.1 km3 = 11.5 miles3
Roughly half the melt remains in the crater , where its average thickness is 116 meters = 380 feet
Visible fireball radius: 34.3 km = 21.3 miles
The fireball appears 78 times larger than the sun
Thermal Exposure: 2.51 x 107 Joules/m2
Duration of Irradiation: 45.6 seconds
Radiant flux (relative to the sun): 550
Effects of Thermal Radiation:
Clothing ignites Much of the body suffers third degree burns Newspaper ignites Plywood flames Deciduous trees ignite Grass ignites
Richter Scale Magnitude: 8.7
Mercalli Scale Intensity at a distance of 100 km:
IX. General panic. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. Serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters. X. Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.
The ejecta will arrive approximately 144 seconds after the impact.
Average Ejecta Thickness: 2.92 m = 9.58 ft
Mean Fragment Diameter: 22.8 cm = 8.97 inches
The air blast will arrive at approximately 303 seconds.
Peak Overpressure: 851000 Pa = 8.51 bars = 121 psi
Max wind velocity: 697 m/s = 1560 mph
Sound Intensity: 119 dB (May cause ear pain)
Which is long talk for: you’ll be boiled, shaken by a 8.7 quake, hit by ejecta fracments 30cm big, hit by wind going 697 m/s (2509.2 km/h). A.k.a. you’ll die.