Dating mt st helens rocks
At such speeds, the projecticle explodes on impact and carves out a round bowl-shaped depression on the surface. How can you distinguish an impact crater from a volcanic crater?Volcano craters are above the surrounding area on mountaintops while the craters from impacts are below the surrounding area with raised rims.
Impacts as large as the one that led to the demise of the dinosaurs in much more recent history were happening about once a month. Select the photographs to display the original source in another window.There are still small chunks of rock orbiting the Sun left over from the formation of the solar system.This assumes, of course, that the cratering rate has been fairly constant for the last few billion years.The heavy bombardment of about 3.8 billion years ago must be taken into account when using the crater age dating technique.The rock on the surface of the planet or moon is bent backward, upward, and outward so the amount of material ejected is much larger than the projectile.
Large craters will have a central peak formed by the rock beneath the impact point rebounding upward and they may also have terracing of the inner walls of the crater from the collapsing of the crater rim inward.
Volcanism is any eruption of molten lava onto the surface.
The molten rock has a lower density than solid rock so it rises.
The longer the surface has been exposed to space, the more craters it will have.
If you know how frequently craters of a given size are created on a planet or moon, you can just count up the number of craters per unit area.
The size of the craters having central peaks depends on the gravity of the planet or moon: on the Moon craters larger than about 60 kilometers in diameter have central peaks while the crater diameter on the Earth needs to be larger than just 1 to 3 kilometers.