File:Black porphyritic dacite (upper Holocene, 14 May 1915; Devastated Area, Lassen Volcano National Park, California, USA) 51.jpg

Original file (4,000 × 3,000 pixels, file size: 7.04 MB, MIME type: image/jpeg)

Summary

Description
English: This is lava from Mt. Lassen (Lassen Peak), a prominent volcano and the key scenery in Lassen Volcanic National Park. Lassen Volcano is part of the Cascade Range, a north-south linear chain of active and potentially active volcanoes in America's Pacific Northwest. It extends from northern California to Oregon, Washington State, and into British Columbia, Canada. The Cascade Range formed as a result of tectonic subduction - the offshore Juan de Fuca Plate is diving below the North American Plate. The diving plate causes melting in the mantle. The melt rises and emerges at the surface at volcanic centers. Famous Cascade Range volcanoes include Mt. St. Helens, which had a large eruption in May 1980, Mt. Rainier near Seattle, Mt. Hood, which is the highest peak in Oregon, and Mt. Mazama, which destroyed itself 7,700 years ago in an enormous eruption that produced the modern-day Crater Lake Caldera (also a national park).

Mt. Lassen is a large volcanic dome that developed by lava extruding along the northeastern flanks of a former Cascade Range feature called Brokeoff Volcano (also known as Tehama Volcano). Brokeoff Volcano is an andesitic-dacitic subduction zone stratovolcano (composite volcano). Stratovolcanoes usually have violent, explosive ash eruptions. They tend to erupt igneous materials of intermediate chemistry (between felsic and mafic). Brokeoff Volcano was active from about 4 million years ago, during the Pliocene, to about 400,000 years ago. Only the caldera exists today. Calderas are large holes or depressions left behind after a volcano destroys itself or collapses. The Brokeoff Caldera is an erosional and slow-collapse caldera that formed before about 350,000 years ago.

The Mt. Lassen volcanic dome first started forming in the Late Pleistocene, at about 29 ka. It is principally composed of dacite lava, an extrusive igneous rock that is usually porphyritic-textured. Dacite is between andesite and rhyolite in silica content. Activity through time has ranged from dacite lava extrusion to explosive ash eruptions. Mt. Lassen last experienced eruptive activity in the early 1900s (1914 to 1921).

The lava boulder shown here is in a volcanic debris flow deposit from 19 and 22 May 1915, when Mt. Lassen last had a significant eruption. The deposit consists of fine sediments, cobbles, and boulders, some of which are quite large. Clasts in the flow deposit include pinkish-reddish porphyritic dacite and gray porphyritic dacite, both of which formed at 27 ka during the Late Pleistocene, early in Mt. Lassen's history. Another clast type in the deposit is black porphyritic dacite, shown here, that formed on 14 May 1915. The whitish-colored phenocrysts (click on the photo to zoom in and look around) are plagioclase feldspar.

Locality: boulder in Devastated Area, Lassen Volcano National Park, northeastern California, USA
Date
Source https://www.flickr.com/photos/47445767@N05/36866142354/
Author James St. John

Licensing

w:en:Creative Commons
attribution
This file is licensed under the Creative Commons Attribution 2.0 Generic license.
You are free:
  • to share – to copy, distribute and transmit the work
  • to remix – to adapt the work
Under the following conditions:
  • attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/36866142354. It was reviewed on 20 October 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

20 October 2020

Captions

Add a one-line explanation of what this file represents

Items portrayed in this file

depicts

15 July 2010

image/jpeg

0.002 second

18.6 millimetre

88a93fa749114e04371a878bbcb8346fd3ce9ed0

7,379,104 byte

3,000 pixel

4,000 pixel

File history

Click on a date/time to view the file as it appeared at that time.

Date/TimeThumbnailDimensionsUserComment
current01:50, 20 October 2020Thumbnail for version as of 01:50, 20 October 20204,000 × 3,000 (7.04 MB)Ser Amantio di NicolaoUploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/36866142354/ with UploadWizard

The following page uses this file:

Metadata