what type of glacier forms a u shaped valley
U-shaped valley U-shaped valleys, trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular.[1] They have a characteristic U shape, with steep, straight sides and a flat or rounded bottom (by contrast, valleys carved by rivers tend to be V-shaped in cross-section). Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring.[2] When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice, called glacial till or glacial erratic.
Valley A valley formed by flowing water, or river valley, is usually V-shaped. The exact shape will depend on the characteristics of the stream flowing through it. Rivers with steep gradients, as in mountain ranges, produce steep walls and a bottom. Shallower slopes may produce broader and gentler valleys. However, in the lowest stretch of a river, where it approaches its base level, it begins to deposit sediment and the valley bottom becomes a floodplain.
Mount St. Helens With the recent volcanic activity starting in 2004, the glacier lobes were pushed aside and upward by the growth of new volcanic domes. The surface of the glacier, once mostly without crevasses, turned into a chaotic jumble of icefalls heavily criss-crossed with crevasses and seracs caused by movement of the crater floor.[15] The new domes have almost separated the Crater Glacier into an eastern and western lobe. Despite the volcanic activity, the termini of the glacier have still advanced, with a slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe. Due to the advance, two lobes of the glacier joined together in late May 2008 and thus the glacier completely surrounds the lava domes.[15][16][17] In addition, since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice onto its surface below; there are two rock glaciers to the north of the eastern lobe of Crater Glacier.[18] Crater Glacier is the only known advancing glacier in the contiguous United States.[19]
Backshore Sediments in this area are well-sorted and well-rounded. Its grain sizes are mainly coarse sand and medium sand, which are larger than that in littoral barrier dune.The sedimentary structures include parallel bedding and low-angle cross-bedding.