After the recent tsunami disasters (Aceh, Pangandaran, Palu, Krakatau and other places) voices that are warning of a tsunami threatening Jakarta (eg. in Kompas, December 27th, page 21) or even all of Indonesia are being heard. In short: Jakarta is safe and the all-Indonesia-tsunami is nothing but a hoax.
Let me explain. To produce a tsunami, three things have to come together: Water, a trigger and a deep water setting that is close to shore. Tsunamis can be triggered by an earthquake (e.g. Aceh, 2004) or a submarine landslide (e.g. Biak,1996, Palu, 2018, Banten, 2018), an exploding volcano (e.g.Tambora, 1815, Krakatau 1883) or an asteroid impact (Madagascar, 4,800 y. B.C.?).
If this trigger happens in deep (marine) waters, it generates a wave which is – initially – not particularly high, but travels very fast. As this wave propagates into shallower water, it slows down and at the same time the wave becomes higher, several meters or tens of meters that run ashore – a tsunami. It is important to note, that this can only happen in places where deep sea is adjacent to shore. The mechanism causing high tsunami waves at the beach is actually similar to the swell causing surf-waves.
Indeed, if we plot on a map of where tsunamis have occurred (worldwide and in Indonesia), these are always areas, where deep oceans are close to land. In other words, there are not and cannot be tsunamis in shallow water, it is a law of nature. The Java Sea and Malacca Strait are shallow. Water depths are less than hundred meters over most of the area, not enough for a tsunami. Moreover, there are no volcanoes in the Java sea and Malacca Strait that could trigger tsunami waves.
We can summarize that Jakarta and the entire north coast of Java (Cirebon, Semarang, Surabaya) and the north-east coast of Sumatra (Langsa, Dumai, Tebingtinggi, etc.) is safe from tsunamis. With the same logic this applies also to West Kalimantan (Pontianak) and South Kalimantan (Banjarmasin).
To conclude, yes, there are many dangers in Jakarta, earthquakes, collapsing bridges and falling billboards, traffic accidents with fire (e.g. Bintaro, 1987), flooding from rainwaters (every year), buses without brakes or drugged drivers that run into pedestrian groups (e.g. Gambir, 2012) – so many things that could go wrong, but a tsunami is the least worry in Jakarta.