Earth Impact Effects Program

Robert Marcus, H. Jay Melosh, and Gareth Collins

Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article

Your Inputs:

Distance from Impact: 48.30 km ( = 30.00 miles )

Projectile diameter: 500.00 meters ( = 1640.00 feet )

Projectile Density: 8000 kg/m³

Impact Velocity: 22.00 km per second ( = 13.70 miles per second )

Impact Angle: 56 degrees

Target Density: 1000 kg/m³

Target Type: Liquid water of depth 3.3 km ( = 2.0 miles ), over crystalline rock.

Energy:

Energy before atmospheric entry: 1.27 x 10²⁰ Joules = 3.03 x 10⁴ MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 3.1 x 10⁵years

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 tilt of Earth's axis (< 5 hundreths of a degree).

The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:

The projectile begins to breakup at an altitude of 18300 meters = 60100 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 21.9 km/s = 13.6 miles/s

The energy lost in the atmosphere is 9.73 x 10¹⁷ Joules = 2.32 x 10² MegaTons.

The impact energy is 1.26 x 10²⁰ Joules = 3.00 x 10⁴MegaTons.

The larger of these two energies is used to estimate the airblast damage.

The broken projectile fragments strike the ground in an ellipse of dimension 0.653 km by 0.542 km

Crater Dimensions:

What does this mean?

The crater opened in the water has a diameter of 16.1 km ( = 9.98 miles ).

For the crater formed in the seafloor:

Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 5.52 km ( = 3.43 miles )

Transient Crater Depth: 1.95 km ( = 1.21 miles )

Final Crater Diameter: 6.93 km ( = 4.31 miles )

Final Crater Depth: 530 meters ( = 1740 feet )

The crater formed is a complex crater.

The volume of the target melted or vaporized is 0.0677 km³ = 0.0162 miles³

Roughly half the melt remains in the crater, where its average thickness is 2.83 meters ( = 9.27 feet ).

Thermal Radiation:

What does this mean?

Time for maximum radiation: 457 milliseconds after impact

Visible fireball radius: 9.84 km ( = 6.11 miles )

The fireball appears 46.3 times larger than the sun

Thermal Exposure: 2.51 x 10⁷ Joules/m²

Duration of Irradiation: 2.17 minutes

Radiant flux (relative to the sun): 193

Effects of Thermal Radiation:

Clothing ignites

Much of the body suffers third degree burns

Newspaper ignites

Plywood flames

Deciduous trees ignite

Grass ignites

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 9.66 seconds after impact.

Richter Scale Magnitude: 6.8

Mercalli Scale Intensity at a distance of 48.3 km:

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.

Ejecta:

What does this mean?


The ejecta will arrive approximately 1.66 minutes after the impact.

At your position there is a fine dusting of ejecta with occasional larger fragments

Average Ejecta Thickness: 7.36 cm ( = 2.9 inches )

Mean Fragment Diameter: 29.8 cm ( = 11.7 inches )

Air Blast:

What does this mean?


The air blast will arrive approximately 2.44 minutes after impact.

Peak Overpressure: 271000 Pa = 2.71 bars = 38.5 psi

Max wind velocity: 351 m/s = 784 mph

Sound Intensity: 109 dB (May cause ear pain)

Damage Description:

Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Highway truss bridges will collapse.

Glass windows will shatter.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.

Tsunami Wave:

What does this mean?

The impact-generated tsunami wave arrives approximately 4.8 minutes after impact.

Tsunami wave amplitude is between: 121.0 meters ( = 398.0 feet) and 374.0 meters ( = 1230.0 feet).

Click here for a pdf document that details the observations, assumptions, and equations upon which this program is based. It describes our approach to quantifying the important impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The processes included are: atmospheric entry, impact crater formation, fireball expansion and thermal radiation, ejecta deposition, seismic shaking, and the propagation of the atmospheric blast wave.

Recent improvements in the airblast calculation are described here.