The earths plates move by 'Ridge-Push' and 'Slab Pull'. At constructive plates margins, lava is extruded and new crust forms as the convection pushes the hot magma though and the slab pull is where the dense subducted plate pulls the rest of the plate along. That is the very basics of what happens. Lamp A - Off - The lava is cold, and therefore does not flow or convect. Lamp B - On - The lava at the bottom by the light is being heated, as it heats, it gets less dense and rises to the top. When at the top, it cools down, and gets more dense and then falls back to the bottom again. Convection. The heat source of the lava lamp is the light giving heat energy. The heat source in the earth is the core, and the radioactive processes (Mainly radioactive decay) that occurs within it. The lava in the lamp represents the earths mantle. The floating pieces are trying to be the earths crustal plates, and they would move over the lava (earths mantle) due to the convection. and thats how lava lamps are made