River cuts deep into its bed after Noto earthquake

On January 1, 2024, a big earthquake hit the Noto Peninsula^*1, a part of Japan that sticks out into the sea. The earthquake had a magnitude^*2 of 7.5. In the north and west of the peninsula, the land rose by up to 5.2 meters. Now a group of researchers^*3 says this rising land changed a river very fast. They watched a "waterfall" move almost one kilometer up the river in less than one year.

The researchers come from eight universities and research centers in Japan. Tohoku University led the group. The leader is Takahashi, an assistant professor^*4 at the university's International Research Institute of Disaster Science. The group announced the results on September 16, 2026. Their paper appeared in the journal^*5 Communications Earth & Environment on September 14. Anyone can read it for free.

The group studied the Hakka River in the west of the peninsula. At the mouth of this river, the land rose by almost 4 meters. So the end of the river was suddenly much higher than the sea. The water fell down this step like a waterfall.

The researchers studied about one kilometer of the river, from the mouth going inland. They used radar^*6 images from right after the earthquake and photos taken from the air. They also flew drones^*7 over the river many times. The drones used lasers^*8 and cameras to make 3D models^*9 of the land. The researchers compared the models over time.

The results were surprising. In less than one year, the river cut its bed down by up to 2 meters. The top of the "waterfall" moved up to 770 meters up the river. Floods^*10 did most of the work. The waterfall jumped up the river during heavy rain in July 2024, and again during very heavy rain on September 20 to 22, 2024. That rain came about eight and a half months after the earthquake and caused big floods in many rivers in the area. Today the waterfall has reached a small dam^*11 built by people, and it has stopped there.

The river cut so deep that it uncovered old layers of sand and mud. These layers were left near the river mouth about 7,400 years ago, in the Jomon period. The old riverbed was left high above the new river. This makes a new river terrace^*12. The researchers say this is the first time in the world that anyone has watched a river terrace form so soon after an earthquake, and in such fine detail. It shows that terraces on the coast and terraces along a river can form at almost the same time.

The researchers also saw other changes. The river washed away the fine sand and mud first. Big stones and broken pieces of concrete^*13 stayed on the riverbed. This hard layer slowed the cutting down for a time. But the water then cut into the banks^*14 on both sides. The river became more than 60 meters wide.

More than two and a half years have passed since the earthquake. The researchers say the riverbed may keep going down, and the river may keep getting wider, for more than ten years. This could happen along about 10 kilometers of the Hakka River from its mouth. The water has already damaged the ground near the dam and near the posts that hold up bridges. Some walls along the banks have already fallen down. The researchers say the same thing is very likely happening in other rivers in the north of the Noto Peninsula.

1. *1 peninsula: A piece of land with water on three sides
2. *2 magnitude: A number that shows how strong an earthquake is
3. *3 researchers: People who study something carefully to learn new things
4. *4 assistant professor: A teacher and researcher at a university
5. *5 journal: A magazine where researchers print their work
6. *6 radar: A machine that uses radio waves to make pictures of the ground
7. *7 drones: Small flying machines with no pilot inside
8. *8 lasers: Thin lines of strong light used to measure things
9. *9 3D models: Pictures on a computer that show the shape of the land in three dimensions
10. *10 floods: Times when a lot of water covers land that is usually dry
11. *11 dam: A wall built across a river to hold back water
12. *12 terrace: A flat step of land that is higher than the land next to it
13. *13 concrete: A hard, gray building material made from sand, small stones, cement and water
14. *14 banks: The land along the sides of a river