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Below I've circled (in yellow) what looks like two fountains just before the Super Heavy launch. They start at T-5 seconds, just a fraction of a second before the water deluge can be seen on the launch pad. They can be seen on this video at the 9:48 mark.
That's the location of the two relief valves used to control the initial flow of deluge water to the steel plate underneath the orbital launch mount. As the water starts flowing the relief valves are opened to control the flow of water, then immediately before engine ignition the relief valves are closed in order to achieve maximum pressure.
