Mountain Terrain, Weather, and Hazards

examples of fold mountains. When the squeezing of a range is intense, the rocks of the mountain mass first
fold but then may break, and parts of the rocks are pushed sideways and override neighboring formations.
This explains why older rocks are often found perched on top of younger ones. Isolated blocks of the over
thrust mass may form when erosion strips away links connecting them with their place of origin. Almost
every range of folded mountains in the world exhibits an over thrust of one sort or another.

Volcanic Mountains
1-26. Along convergent plate boundaries volcanic activity increases. As it is forced underneath an
overriding neighbor, continental crust melts and turns to magma within the mantle. Since it is less dense
than the surrounding material, it rises and erupts to form volcanoes.

These volcanoes are found in belts, which correspond to continental margins around the world.
The best known is the “Ring of Fire” encircling the Pacific Ocean from Katmai in Alaska
through the Cascades (Mount Rainier and Mount Saint Helens) down through Mexico’s
Popocatepetl to the smokes of Tierra del Fuego. This belt then runs west down the Aleutian
chain to Kamchatka, south to the volcanoes of Japan and the Philippines, and then east through
New Guinea into the Pacific. Smaller volcanic belts are found along the Indonesian-Southeast
Asian arc, the Caucasus region, and the Mediterranean.

Volcanic activity also arises at boundaries where two plates are moving away from each other,
creating deep rifts and long ridges where the crust has cracked apart and magma wells up to
create new surface material. Examples of this are the Mid-Atlantic Ridge, which has created
Iceland and the Azores, and the Rift Valley of East Africa with Kilimanjaro’s cone.

Complex Mountains
1-27. Most ranges are complex mountains with portions that have been subject to several processes. A
block may have been simply pushed upward without tilting, with other portions folded, domed, and faulted,
often with a sprinkling of volcanoes. In addition, these processes occur both at the macro and the micro
level. One massive fold can make an entire mountain peak; however, there are folds measured by a rope
length, and tiny folds found within a handhold. A mountain front may be formed from a single fault, but
smaller faults that form ledges and gullies may also be present.

ROUTE CLASSIFICATION
1-28. Military mountaineers must be able to assess a vertical obstacle, develop a course of action to
overcome the obstacle, and have the skills to accomplish the plan. Assessment of a vertical obstacle
requires experience in the classifications of routes and understanding the levels of difficulty they represent.
Without a solid understanding of the difficulty of a chosen route, the mountain leader can place his life and
the life of other Soldiers in extreme danger. Ignorance is the most dangerous hazard in the mountain
environment.
1-29. In North America the Yosemite Decimal System (YDS) is used to rate the difficulty of routes in
mountainous terrain. The YDS classes are—

Class 1―Hiking trail.

Class 2―Off-trail scramble.

Class 3―Climbing, use of ropes for beginners (moderate scrambling).

Class 4―Belayed climbing (moderate to difficult scrambling, which may have some exposure).

Class 5―Free climbing (requires climbers to be roped up, belay and emplace intermediate
protection).

Class 5 is further subdivided:

Class 5.0-5.4―Little Difficulty. This is the simplest form of free climbing. Hands are
necessary to support balance. This is sometimes referred to as advanced rock scrambling.

Class 5.5―Moderate Difficulty. Three points of contact are necessary.

Class 5.6―Medium Difficulty. The climber can experience vertical position or overhangs
where good grips can require moderate levels of energy expenditure.

26 July 2012

TC 3-97.61

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