Ice cubes float in water because they are less?

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

i think the answer is

mass

volcanoes (an event in the geosphere) release a large amount of particulate matter into the atmosphere. these particles serve as nuclei for the formation of water droplets (hydrosphere). rainfall (hydrosphere) often increases following an eruption, stimulating plant growth (biosphere).