Deep beneath the upper visible layer a small crevice develops. It is gradually widened as more and more little pieces of gravel travel to its beginnings. As they settle they force the two sides apart. They scrape and scratch as they find their niche in the ever growing internal crevice. The places that they damage become raw and easily irritated with further touch.
Over time water seeps in and settles in the spaces between the gravel. It is joined by lava that bursts hot onto the surface then dies down quickly as the water cools it. Sometimes there is no sign that the lava has erupted and other times there is a scar that remains raw and vulnerable.
No one sees the seething mass of water, lava and gravel but it is felt by those who carry it. Deep within them, unseen but niggling like a slither of glass lodged in your foot. Each step inches it in deeper. Its presence changes your walking stance. Your motivation to walk is dictated on how painful it is.
It can be a single last piece of sand settling to the slowly filled crevice that is the final piece before everything thrusts upward and with velocity. All the sediment becomes airborne no longer able to be borne settled deep within.
Everything and everyone in close proximity is suddenly coated. There is no innocent bystander, there is only duck and cover. The name of this eruption from buried deep within is simply ANGER.