There are more than one term for a deep narrow valley. Glens, canyons, ravines, fjords are terms you could use.
A narrow valley is a V-shaped valley, or river valley. A narrow valley has steep sloped sides that look like the letter V. They are formed by a strong stream.
The different types of river valleys include V-shaped valleys, U-shaped valleys, and canyon valleys. V-shaped valleys are typically narrow with steep sides, carved by erosion from a river. U-shaped valleys are wider and have more gradual slopes, formed by glaciers. Canyon valleys are deep and narrow with steep sides, often formed by a combination of tectonic activity and erosion.
They are called trenches.
A deep valley with steep sides would be called a gorge or canyon.
Trenches, or deep sea trenches.
a deep, steep-sided, narrow river valley
The term used for narrow deep valleys is "ravine."
a glen
Those deep valleys are mainly in Wales, in the southwest of Britain.
Ravine
Ravines.
The deep narrow valleys on the Moon are called rilles. These are long, winding depressions that can stretch for many kilometers across the lunar surface. Rilles are thought to have been formed by a combination of ancient volcanic activity and tectonic forces.
deep narrow valleys and mountains
Ravine, gorge, canyon.
A narrow valley is a V-shaped valley, or river valley. A narrow valley has steep sloped sides that look like the letter V. They are formed by a strong stream.
deep sea canyons
A ditch with deep sides is commonly referred to as a "gorge" or "ravine." These terms describe narrow, steep-sided valleys that are typically formed by the erosion of rock and soil by a river or other water flow. In some contexts, a "trench" may also be used to describe a similarly deep and narrow excavation.