Igneous Rock Tuff

Mineral Sciences

Catalog Number:
401523
Object/Specimen Description:

These fragments are examples of a ignimbrite, which are synonymous with welded tuffs. The largest fragment measures around 20 cm x 14 cm x 5 cm in size, and the other fragments measure the same or less in size.

Specimen Count:
3
Collector:
A. Blankenbicker
Precise Locality:

White River Quarry

Locality:
US Pacific (CA, OR, WA)
Collecting Date:
15 May 2014
Collecting Locality:
North America, United States, Washington, King County
Cabinet:
25
Drawer/Shelf:
01
Artist interpretation of volcanism in the Ancestral Cascades, in North West United States.
Map of the western United States showing the inferred extent of Cenozoic ancestral and modern Cascades magmatic arcs in Washington, Oregon, California, and Nevada.
This dam in Washington, USA, is constructed primarily from basalt from a quarry that mines the Ancestral Cascades.
Volcanic rock quarry in Washington. Dark gray basalt covered by volcanic ash and soil. Location: White River Quarry, Enumclaw, WA.
Volcanic rocks used to protect harbor in Washington, USA.
Detailed geologic time scale.
Graphic representation of geologic time, with some well-known fossils

The White River Quarry is made up of basalt lava flows that date back to 25 million years ago and is part of what is known as the Ancestral Cascades. This time pre-dates the more well-known volcanoes in the area such as Mt. St. Helens, Mt. Rainier, and Mt. Adams. Above the old basalt lava flows are layers of younger sediments, including those deposited by glaciers and rivers, more recent eruptions, and a 4,800-year-old volcanic mudflow that covers areas all the way from Mt. Rainier to Tacoma, Washington. The old volcanic rock is very hard and dense, which makes it very useful for construction projects.

Colima volcano, in Mexico, on November 22, 1998. A collapsing lava flow broke into a pyroclastic flow, reaching 4.5 kilometers (3 miles) from the summit.
This log was burned by a pyroclastic flow 5,600 years ago. The age was calculated using carbon dating techniques. Location: White River Quarry, Enumclaw, WA.
Pyroclasitc flow at Mayon Volcano, Spet. 15, 1984. Philippines.
Artist interpretation of volcanism in the Ancestral Cascades, in North West United States.
Volcanic rock quarry in Washington. Dark gray basalt covered by volcanic ash and soil. Location: White River Quarry, Enumclaw, WA.

During an explosive eruption, a volcano ejects very hot ash, rock, pumice, and gas. This mixture can be directed up to the sky as an eruption column, or it can fall back to earth. When it falls to the ground, or when it is directed laterally (sideways), it produces a pyroclastic density current (PDC), commonly called a pyroclastic flow. These flows can move faster than 100 km/h (60 mph). Because they are loaded with rocks and pumice they can destroy almost anything in their path including trees and buildings. These are one of the most hazardous volcanic processes and have claimed many human lives. Sometimes PDCs deposit ash, pumice, and rock that are hot enough to melt back together. If such deposits are thick enough, the pumice are squeezed flat.