silica
caldera
viscous
denser
subduction
divergence
hot spots
earthquakes
Explosions from composite volcanoes occur as a result of gas buildup within them. Shield volcanoes also may erupt explosively if water accumulates inside their vents.
Reflection and Refraction are what makes objects further than they apper.
A biggie: the transcontinental railroad. Because it would economically improve wherever it was, both the North and the South competed for the railroad to be in their respective territory, evidenced by the Kansas-Nebraska Act and the Gadsen Purchase and induction of California as a free state in 1860.
In addition: people could get land cheap because it was abundant and might leave to start afresh economically.
There's other stuff I can't remember as clearly, but there's a little and I hope it helps :)
Because they have the most direct sunlight possible.
Precious gems would be my best guess, it's the only natural rescource that's only in one area. Sooo.... Precious gems i guess
