Describe one way that incised meanders form.?

Answer 1

http://walrus.wr.usgs.gov/infobank/programs/html/school/moviepage/18.02.10.html
USGS site sourced from Annenberg/CPB Resources - Earth Revealed - 20. Running Water II: Landscape Evolution

An "incised meander" can be produced as a result of rejuvenation and uplift. Incised meanders differ from normal meanders because they are cut below the level of a river's former floodplain. They result from down-cutting along the deepest part of a river's channel, the "thalweg." The down-cutting is so rapid that the river preserves a meandering pattern while deepening its valley.

Answer 2

What is above is correct. An example is after an ice age. The weight of ice is lifted off the land which gradually rises, this makes the gradient of the river steeper so the river has more energy which is used to erode downwards creating an incised meander.
This can also happen if the land is raised for instance by tectonic uplift as the plates collide