Mountains in motion: an ever-changing environment

The North Cascades are still rising, shifting and forming. Geologists believe that these mountains are a collage of terranes, distinct assemblages of rock separated by faults.

Fossil and rock magnetism studies indicate that the North Cascades terranes were formed in other places, some many thousands of miles south of here. Attached to slowly moving plates of oceanic rock, they drifted northward merging together about 90 million years ago. Exactly when they arrived here is still in question.

Colliding with the North American Continent, the drifting rock masses were thrust upwards and faulted laterally into a jumbled array of mountains. The collision broke or sliced the terrain into north or south trending faults that are still evident today where State Route 20 (SR 20) crosses the Straight Creek fault just east of Marblemount.

Geologists believe the rocks to the west of the fault slid more than 100 miles north of the slice to the east. The rocks to the east of Straight Creek Fault are gneisses and granites, while those to the west are completely recrystallized mudstones and sandstones. Over time, these precursors to today's North Cascades were further faulted and eroded to a nearly level plain.

During the past 40 million years, heavier oceanic rocks thrust beneath the edge of this region. Intense heat at great depths caused them to melt. Some of the melt rose to the surface in fiery volcanic eruptions at locations like Mt. Baker. The rest recrystallized at various depths to form vast bodies of granite rock.

The North Cascades have again pushed upward to majestic heights, exposing the roots of the ancient collision zone. Ice, water and wind will eventually level the se peaks, returning them bit by bit to the sea.

The rocks of the North Cascades comprise some of the most complex and least understood geology in North America. By studying the rock types found in the area and mapping the locations of the rock outcrops a "geologic picture" slowly takes form.

For more information on both the variety of rock types here and the North Cascades geologic history, look under the relief map in the North Cascades Visitor Center or at the rock display at the Diablo Lake Overlook. At the overlook notice the striking rock outcrop across SR 20. You can see lighter colored intrusions that were injected into the darker "country" rock.

Visit the park website at http://www.nps.gov/noca/geology.htm or purchase new reference books available through Northwest Interpretive Association.

Combining air and water

Water and air form the foundation of the North Cascades ecosystemchanges in their quality affect everything. Water and air are almost inseparable, as water travels through air and air travels through water. The water cycle - precipitation, saturation, evaporation, and condensation - links air and water.

Salmon and trout, in order to survive, require relatively high levels of oxygen in their waterthe water must be aerated.

Glaciers and snowfields in the North Cascades are links in the cycle of water and air. Meltwater from this ice and snow flows down streams, creeks, rivers to estuaries and on to the ocean. From the ocean, water evaporates and travels as clouds, which are blown into the mountains, depositing their water as snow or rain. The cycle is never broken.

North Cascades National Park air quality is rated Class I, or "most pristinea rating which the National Park Service works to maintain. Resource Managers monitor ground-level ozone and other indicators of air quality from stations at Marblemount, Lake Chelan, and Ross Lake. Rainwater is tested weekly to determine levels of acidity and chemical content.

Existing water quality within North Cascades National Park Service Complex is believed to be excellent. However, the waters do receive acid deposits and other air pollutants. Air pollution from vehicles, industry, wood-burning, and other sources can end up in snowfields, glaciers, and throughout watersheds. These airborne pollutants are deposited by rain and snowfall, and by the air itself. Rivers, lakes, and streams are monitored regularly for chemical content. Macroinvertebrate samples are taken in order to gauge water quality.

For more information pick up the Air Quality brochure or visit the website at http://www.nps.gov/noca/air.htm

Carved by ice

The fantastic jumble of serrated ridges, saw-toothed peaks and deep cirques is the result of several ice ages. Fifteen thousand years ago vast sheets of ice reached from central British Columbia into what are now the North Cascades. As the gigantic glaciers advanced they dragged rocks ranging in size from grains of sand to house-sizes boulders, sculpting and scouring the landscape beneath them. Glacial sculpting continues today on a smaller scale. Glaciers leave behind these mountain features:

• Cirque: Horseshoe-shaped recess at the head of a valley.(e.g. Horseshoe Basin, Boston Glacier, South Cascade Glacier)

• Arete: Saw-tooth ridge formed between adjacent cirques. (e.g. Ripsaw Ridge, South Picket Range)

• Horn: High pyramidal peak formed by cirques on three or more sides. (e.g. Mt. Shuksan, Forbidden Peak)

• Tarn: Deep rounded lakes occupying evacuated cirques. (e.g. Doubtful Lake, White Rock Lakes, Hidden Lake)

• Moraine: Accumulation of rock material on or around a glacier, derived from rockfall and from erosion of the valley sides by the glacier.