Recall from the huge tsunami from 2004, that the ocean receded significantly just prior to it returning with such devastating effects
On this recent one a few days ago that occurred “without warning”, did the water recede? I’ve heard nothing of the sort, and it may have given at least a few minutes warning. But I’d like to have confirmation that it either did or did not significantly pull back before crashing forward.
It may be different because this one was triggered by the major landslide on Little Krakatoa, rather than by an undersea earthquake, but I’d be interested in the answer as well.
I didn’t see mention of whether there was a recession, but I did see some discussion of why the early warning system isn’t very effective - it is based on earhquakes, and not every tsunami is caused by earthquakes (underwater landslides is one example). The current system still tends to have a large number of false negatives and positives. Also, not as relevant in this case, but there is also a difference between tsunamis which are caused by fairly sudden disturbances, and tidal waves which are weather related.
To be more effective, there probably needs to a series of redundant systems, seismic detectors paired with water elevation bouys and perhaps even some sort of satellite sensors.
Also, by the time the water starts receeding, isn’t any warning going to be too late?
Tsunamis are caused by the displacement of underwater “land”, whether by earthquake or landslide. Not all earthquakes cause tsunamis because they don’t always displace anything or not enough of it. A small underwater landslide won’t cause one either.
If there was a tsunami, you always get water receding before it comes in. How much it recedes depends on how much energy it has, with more recession for higher energy.
As I understand it, the “no warning” complaint was about “no official warning”.
I got the impression that in the stricken area, the water did not recede prior to the first wave, although it may have from another area, possibly uninhabited which is why nobody noticed that.
A large landslide would force a lot of water forwards, no recession necessary.
The tsunami hit about 9:30 in the evening, which should be after sunset there. The water could have receded without anyone noticing. It’s not like it makes some unusual noise or anything like that.
Wouldn’t whether the first noticeable phase of the wave to hit was a peak or a trough depend on the nature of the underwater disturbance? If there was an earthquake, I would reasonably expect it to be 50% likely that there was now more space for water to fill rather than less, so the wave would start out a trough, but it might also be true that earthquakes tend to produce these more often than not. In the case of landslides though, I would expect the first part of the wave to be a peak. I’m not as sure, but I would expect this to be the case whether a place was hit directly from the point the waves radiated from, or whether it was a wave bent around some land. I suppose after the waves were far enough away that the two waves that bent around land started to interact with each other, whether a peak or trough would arrive first might become random. Of course, it’s more likely that I’m way out of my depth (pun not initially intended) on this.
No one reported seeing water receding, and the Indonesian government is always exhorting its citizens to watch for that. No, it was triggered by an underwater landslide, and no warning system could have given a heads-up. Anyone on the beach is just screwed in such an event.
However, it has highlighted how the warning system put in place after the 2004 Boxing Day tsunami has run down through neglect and vandalism. It would not have been able to warn of last weekend’s tsunami, but it is best to have it in working order.
This eyewitness says the water did not recede.
It depends how far away it is. If it’s far enough away, the cliff of water will separate out into slow waves and fast waves. There will be the crashing of small waves along with the crashing of the big wave.
But in real life, even that is a simplification. It’s only in the last 10 years that researchers have been able to demonstrate random solitary waves suddenly appearing in the middle of the ocean.
From what I understand, the tsunami was only about a metre high; the problem was people living and recreating within a metre of the shoreline when the wave hit. At 4 a.m. on a Tuesday in March, you’d have many fewer deaths. I’ve read news reports from eyewitnesses who said they were able to run to higher ground when they heard the wave coming on like a freight train, this wasn’t a monster wave that would suck a bay dry. But I live in a tsunami zone myself, and I’ve often heard it said that a tsunami is the least survivable of all natural disasters if you’re there when it hits.