earths magnetic field, also known as the geomagnetic field
The cataracts kept lower Egypt from coming up the Nile to trade. It made trade decline between the two.
A hot spot is an area on Earth that exists over a mantle plume.Hot spot volcanoes occur far from plate boundaries. Because the hot spot is caused by mantle plumes that exist below the tectonic plates, as the plates move, the hot spot does not, and may create a chain of volcanoes on the Earth's surface.
