NASA says the precise effect of a 460-foot (140-meter) object hitting the Earth would depend on what the asteroid was made of and the angle of impact.
I recall the opposite being taught- that it doesn't matter the angle or material. When the object hits, its matter is turned to energy; it explodes.
That's why craters appear as circles carved in the ground, even when objects enter at strange angles.
Kinetic energy is misunderestimated by common sense. The effect of impact would depend on net speed. If it hits at the maximum speed meteors are capable of, much of the material would be ionized. The flash of light would be like the sun and might endure for hours. At lower speed the material would be vaporized rather than ionized. In no case would more than a fraction of a percent of the mass be converted to energy.
--the "matter" of the asteroid remains "matter" since there is no nuclear reaction involved--the kinetic energy of the meteor is expended as heat and sound and in a massive explosion upon impact---
It's a bit more complicated than that. First, no "matter is turned into energy" (ala nuclear fission) -- the kinetic energy of the impacting object (asteroid) is converted into work, excavating a hole in the ground. Second, it's true that most impacts at an angle make a round hole, but if the incidence angle is less than about 5 degrees, you get elliptical craters. Lower than 1 degree and all kinds of weird effects occur -- projectile decapitation, multiple skip impacts, etc.
The composition of the impactor body also has an effect if there is a signifcant variation in density. Dense impactors (like iron meteorites) penetrate deeply into the Earth, excavating with great efficiency and making a large, deep hole. However, fluffy, ice bodies (like cometary cores) might actually "explode" in the atmosphere before they hit, having the effect of an airburst nuclear device, creating wide area of devastation.
A greater angle from vertical means that the meteor has to pass through more atmosphere and more is ablated before it hits the ground.
The material matters because a less dense meteor will have a smaller mass for a given size. A 140-meter styrofoam packing peanut is less worrisome that a 140-meter iron meteor.
Kinetic energy equals 1/2 mass times velocity squared, so a lighter asteroid won't produce as much damage on impact because it has less kinetic energy.
In addition, lighter asteroids will lose much more of their mass while burning up in the atmosphere, while hard ones will hit with a larger portion of their initial mass. Even worse, very heavy asteroids aren't slowed much by our atmosphere, so will hit faster -- and the speed in the equation above is squared so the damage goes up a lot.
That's why craters appear as circles carved in the ground, even when objects enter at strange angles.
Low-angle impacts produce oval craters, but they aren't as common.