The mass number of an element is equivalent to the number of Protons and Neutrons in the element. For example Oxygen has eight protons and neutrons, therefore its mass number is 16. You could also calculate this by simply rounding the atomic weight of the element to the nearest whole number. Oxygen's atomic weight is 15.994, which as you can see, would be rounded to 16 :)
Im not sure but i think its all the above
The hazards from the volcanoes include lava and pyroclastics, tephra and , lahars and climate alteration. Fertile soil and geothermal energy are beneficial results of volcanic eruptions. Much of El Salvador for example is convered with volcanic ash and this has been a fertile growing medium for coffee plants.
