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charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: [Starlink] Small Tonga update X-BeenThere: starlink@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Starlink has bufferbloat. Bad." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 15 Jan 2023 09:41:49 -0000 Off-topic, but given the interest on this list last year, here's an=20 update one year on from Shane Cronin, the lead volcanologist on the=20 Hunga Tonga Hunga Ha'apai volcano, on what they're learned: https://theconversation.com/a-year-on-we-know-why-the-tongan-eruption-was-s= o-violent-its-a-wake-up-call-to-watch-other-submarine-volcanoes-175734 You'll notice that he mentions unanswered questions, in particular a=20 local tsunami of unknown origin that was 18-20 m high. I'm marginally involved with this whodunnit. Basically, they know the=20 height of the wave because the tsunami knocked out an automated weather=20 station on Kanokupolo Peninsula that collected data every 10 minutes and=20 transmitted it back to its Tongan base every hour. The station was=20 located about 20 m above mean sea level and transmitted its last batch=20 of data at 0500 UTC, half an hour after the destruction of the domestic=20 cable but still 44 minutes before the international cable went down. No=20 transmission was received at 0600 UTC, indicating that the station had=20 been destroyed by then. Unfortunately, that one hour time window is a=20 bit large given tsunami travel times. I'd been aware of this for a while, but was contacted in early December=20 by one of the tsunami modellers involved, who filled in a crucial gap in=20 my knowledge: The weather station had actually been sitting on a=20 cellphone tower! Which I hadn't realised so far ... So we're currently=20 trying to find out from Tonga Telecom when exactly that base station=20 went down - or whether in fact they can still reconstruct this a year=20 down the track. For the tsunami folk, a lot hinges on that piece of=20 information, as this'll determine where the waves came from. The caldera=20 collapse that Shane mentions is one option, but one of the problems with=20 this theory is that there is no clear seismic signature. USGS recorded=20 quakes in the area at 4:40 UTC and another at 5:30 UTC, but these had=20 magnitudes of 4.8 and 4.7 respectively, and were both located a bit to=20 the south of the volcano and were also quite deep (10 km, but that seems=20 to be very approximate). So they don't quite fit the bill, apparently. Another marginally comms-related aspect of the eruption aftermath is the=20 damage it's doing to Tonga's power grid. A lot of the local power=20 network runs on poles above ground, and the lines consist of a blank=20 aluminium earth wire and isolated wires carrying the supply current.=20 These run cheek-to-jowl with the earth wire but aren't mechanically=20 bonded to it. What has happened now is that volcanic ash that was=20 deposited on the lines has worked its way to between the earth wire and=20 the insulated wires, and by the rubbing motion in the wind, the ash is=20 working its way into the isolation, progressively breaking it down and=20 causing the lines to short. So they're likely looking at having to=20 exchange much of their overhead cable. Shane told me about this in late=20 November and actually showed be a few samples that the Tonga power=20 people had given him. Plus he was quite concerned about a number of lookalike volcanoes in the=20 area showing signs of activity now. One submarine one they went over had=20 a pre-eruption bathymetry of 11 m below sea level but had inflated to a=20 wee bit less than that. My own little write-up from last year is here:=20 https://dl.acm.org/doi/10.1145/3570748.3570759 --=20 **************************************************************** Dr. Ulrich Speidel School of Computer Science Room 303S.594 (City Campus) The University of Auckland u.speidel@auckland.ac.nz http://www.cs.auckland.ac.nz/~ulrich/ ****************************************************************