It's actually made of the Moon Pool water and was originally made by the Irish mermaid Eva (whom the comet was named after) in 1740; and is again made by Bella, Cleo and Rikki in the show. The tower was used to stop a comet from hitting the earth in both situations.
Tower of Light is seemingly a tower of water made from the Moon Pool. Cleo, Rikki and Bella had devised a plan to recreate the Tower of Light using their mermaid powers.
First, Cleo used her hydrokinetic power to form water in the shape of a pillar and to bring it up. Next, Rikki used her hydro-thermokinetic power to heat up, energize and create thermal pressure from inside the water pillar, causing it to build up electricity. Lastly, Bella's gelidkinetic powers had created shape to control the water and formed a pillar- in combination with the thermal structure inside it. As it formed more pillars circling around them, the girls' powers struggled to intake more and more pressure of the Moon Pool to create a vortex.
Finally, Bella's other power of substanciakinetic had hardened the water, creating a vortex of intense pressure of water and was sent off as "a tower of light" effect. That tower was sent off towards the comet, and knocks it back to the other direction.
|Aerokinesis • Atmokinesis • Combined Atmokinesis • Cryokinesis • Electrokinesis • Pyrokinesis • Tower of Light|