1. Glacial Erosion:

* The Starting Point: Fjords begin as valleys carved by glaciers. These massive ice sheets move slowly, grinding away at the bedrock, creating deep, U-shaped valleys. The glaciers' sheer weight and abrasive power are what create the characteristic steep sides and narrow, deep shape of a fjord.

2. Sea Level Rise:

* Flooding the Valleys: As glaciers melt and retreat, global sea levels rise. This rising sea level floods the glacial valleys, turning them into the deep, narrow inlets that we know as fjords.

3. Post-Glacial Rebound:

* Land Slowly Rising: After the weight of the glaciers is lifted, the landmass begins to rise. This is called "isostatic rebound." In some cases, the land rises faster than the sea level, creating a shallow "threshold" at the fjord's mouth.

4. Other Factors:

* Tectonic Activity: The presence of faults or other tectonic features can influence the shape and formation of fjords.

* Climate: Fjords are typically found in high-latitude regions with cold climates, where glaciers can form and persist.

Key Characteristics of Fjords:

* Deep and narrow: Fjords are much deeper than the surrounding sea.

* Steep sides: They have steep, often almost vertical walls.

* U-shaped: The cross-section of a fjord is typically U-shaped, a legacy of glacial erosion.

* Thresholds: Fjords often have a shallow, rocky threshold at their mouth, created by post-glacial rebound.

So, in essence, fjords are formed by a combination of glacial carving, sea level rise, and land rebound – a testament to the powerful forces that shape our planet.