The Indal River Delta

We had an unexpected day in and around Sundsvall and on the way home went for a walk in the river delta nature reserve. We didn't get as far as we usually do because the path was extremely soggy with rather deep puddles. Some of the puddles were covered in ice and snow. Mostly you could walk on the snow but in places my feet suddenly sank through into the hidden puddle underneath - what fun!
This is one of about 5 channels by which the Indal River reaches the sea.  As you can see the river channels are still ice-covered, but the snow is going from this coastal land. As we walked over this sandy rise I began thinking about how it was formed. I stated wondering about ice-ages and land rise after the ice melted, but when I got home and checked I found the delta was mostly formed in a man-made environmental catastrophe that happened in 1796.
In 1795, about 100 km upstream from the sea, a short canal was dug to bypass a huge rapid on the river. No-one realised the 25 km long,  30 meter deep lake above the rapid had been created by a glacial dam, which had forced the river to take a new route. The new canal was built on top of that dam. In the spring of 1796 floodwaters started flowing through the canal and cut rapidly through the sand and boulder glacial dam. The entire lake emptied away in 4 hours, creating a 25 m high flood wave that swept down the valley for 100 km until it reached the sea. There it dumped all the debris, all the sand, gravel and soil it had ripped up in its journey, creating this river delta.
Sundsvall Airport is built on the upstream section of the delta and in 2014 I blipped a picture of the delta taken from a plane coming in to land.