[konaice]

all potatoes compared to a 400 meter asteroid impacting earth. Even with warning. The events you mentioned are not even in the same ball park. An asteroid of that size would be off the scale. Trust me

Nope. That's not that big, and it also depends on the angle of impact. a 400meter asteroid hitting mid ocean would cause a title wave but other than that the affects would be short lived. Hit on land it would throw a lot of stuff into the atmosphere, but probably not as much as Mt. St. Helens, and certainly not as much as Krakatoa.

[dumpdaschle]

The 1908 Tunguska explosion was supposedly caused by an asteroid only 60 meters in diameter. That event felled an estimated 60 million trees over 2,150 square kilometres but did not leave a crater. It is believed that the asteroid exploded at an altitude of about 8 kilometres.
source - http://en.wikipedia.org/wiki/Tunguska

[dumpdaschle]

From this link - http://www.space.com/scienceastronomy/astronomy/asteroid_paine_september.html

In 1815 a volcano on the Indonesian island of Tambora exploded and produced a crater similar in size to that from a 500-yard asteroid. About 20 cubic miles of ejecta was released (for comparison, the Mount St. Helens explosion in 1980 released about a quarter of a cubic mile of ejecta).

In the case of Tambora, it has been estimated that 10,000 people died directly from the explosion and 80,000 more died in the region from indirect effects, such as starvation. In addition, the ash is thought to have caused the "year without a summer" in 1816, when there were widespread crop failures across North America. The final death toll was probably in the hundreds of thousands. A similar event today might kill millions.