In what may be the most impractical discovery I've ever made, it came to my attention last week that sea caves make serviceable mobile phone amplifiers.
Last weekend I was on a 27m liveaboard dive boat that was cruising California's Channel Islands. One of the best parts of the trip is that mobile phones work only intermittently even along the mainland-facing shores of the island - and most of the time not at all. The freedom from the internet compounds the sedative effects of scuba diving from a rocking boat.
On the last day before heading back to Santa Barbara we found ourselves in remarkably calm water near Santa Cruz Island. The captain took advantage of the weather to pull the boat deep into Painted Cave, a gigantic coastal cave carved from the island by wave action. Depending on who you ask, Painted Cave is the first or second largest (or longest!) sea cave in the world.
As the captain puttered the boat into the cave many of us raced to the front of the boat to snap pictures. Mostly mobile phones, as the big cameras were safely stashed in Pelican cases or awkward underwater lighting rigs.
I pulled up my camera to take a couple of shots when I felt it chirp in my hand. Text message received! I could hear a few other phones around me making noise as well. I don't recall how many bars I had - one or two at the most - but sure enough, the shape of the cave was concentrating the signals from across the water of Santa Barbara enough to restore basic service.
From Santa Barbara to Santa Cruz is something like 74km over open water. While it's not impossible to get an occasional signal, it's generally unusable. (The signal comes from what I presume are the mainland towers, not towers on the island; I believe only Avalon has cell towers on the Channel Islands.) But the shape of the cave, with its sharply descending walls, were acting like a simple reflector. At least that's my theory. If anyone has tried the same thing in Painted Cave I'd love to hear about it.
In the meantime, consider this a free survival tip. If you're ever stuck on warm, dry island, be sure to climb down into the nearest slippery sea cave to see if you can get a signal to the mainland. Just watch out for angry sea lions.