If this cause essay were about a volcanic eruption, it might go something like:
"Pressure and heat built up beneath the earth's surface; the effect of this was an enormous volcanic eruption."
The next example shows an effect essay, one that would explain all the effects that happened after a specific event, like a volcanic eruption.
arrows that lead causes and effects
If this effect essay were about a volcanic eruption again, it might go something like: "The eruption caused many terrible things to happen; it destroyed homes, forests, and polluted the atmosphere.