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: 10.00 km ( = 6.21 miles )

Projectile diameter: 250.00 meters ( = 820.00 feet )

Projectile Density: 1500 kg/m³

Impact Velocity: 14.00 km per second ( = 8.69 miles per second )

Impact Angle: 45 degrees

Target Density: 1000 kg/m³

Target Type: Liquid water of depth 100.0 meters ( = 328.0 feet ), over crystalline rock.

Energy:

Energy before atmospheric entry: 1.20 x 10¹⁸ Joules = 2.87 x 10² MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 4.0 x 10⁴years

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 69400 meters = 228000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 10.5 km/s = 6.55 miles/s

The energy lost in the atmosphere is 5.21 x 10¹⁷ Joules = 1.24 x 10² MegaTons.

The impact energy is 6.82 x 10¹⁷ Joules = 1.63 x 10²MegaTons.

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 1.21 km by 0.853 km

Crater Dimensions:

What does this mean?

The crater opened in the water has a diameter of 3.68 km ( = 2.29 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: 1.81 km ( = 1.12 miles )

Transient Crater Depth: 639 meters ( = 2100 feet )

Final Crater Diameter: 2.26 km ( = 1.4 miles )

Final Crater Depth: 481 meters ( = 1580 feet )

The crater formed is a simple crater

The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 223 meters ( = 732 feet ).

At this impact velocity ( < 12 km/s), little shock melting of the target occurs.

Thermal Radiation:

What does this mean?

At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 2 seconds after impact.

Richter Scale Magnitude: 5.8

Mercalli Scale Intensity at a distance of 10 km:

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

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.

Ejecta:

What does this mean?


The ejecta will arrive approximately 45.2 seconds after the impact.

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

Average Ejecta Thickness: 9.55 cm ( = 3.76 inches )

Mean Fragment Diameter: 6.09 meters ( = 20 feet )

Air Blast:

What does this mean?


The air blast will arrive approximately 30.3 seconds after impact.

Peak Overpressure: 192000 Pa = 1.92 bars = 27.2 psi

Max wind velocity: 278 m/s = 622 mph

Sound Intensity: 106 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 5.3 minutes after impact.

Tsunami wave amplitude is between: 18.4 meters ( = 60.4 feet) and 36.8 meters ( = 121.0 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.