Some Stuff and Links on Volcanoes

(Gabi Laske)

Last modified: 10 Jan 2020 (link to HMY page on plate tectonics added)
Modified: 13 Dec 2017 (link to Artisan Elevators added)
Modified: 03 Dec 2013 (link to Mt. Vesuvius blog added)
Modified: 25 May 2011 (link to Iceland volcano threat added)
DISCLAIMER: This web page is not a complete web site!
It only provides supplemental material (PDF files) that is not distributed in my classes. It shows a few examples of what we find in San Diego County. This web site also holds a few links to exciting volcano web sites for the playful and curious. For more info on volcanoes, go to my SIO15/ERTH15 "Natural Disasters" course web sites:

Downloads (PDF files)

- 2001 course handout (4 pages)
- PDF table of magma types (same as table on page 4 of handout)
- PDF table of largest volcanic eruptions
- PDF table showing the recurrence time of eruptions
- PDF table of basic volcanic features
- PDF geological map of S.D. county
- glossary for this lecture (PDF)

Examples of Intrusive and Extrusive Structures

Intrusive Structures Extrusive Structures
Mt. Woodson, SD county a shield volcano in Iceland
the batholith in Yosemite a composite volcano in New Zealand

Volcanic Features

-the birth of a pyroclastic flow (New Zealand)
-a lava fountain
-Pu'u O'o, a vent of Kilauea erupting since 1983 , also a lava fountain

Igneous Rocks in S.D. county

There are three geological sections in S.D. county:
- the coastal province
- Pensinsular Ranges
- the Desert Slope

download high-res pdf

The Peninsular Ranges are dominated by intrusive rocks (e.g. Mt. Woodson, Iron Mt., Hot Springs Mt.) pushed to the surface during the ~ 70 Mio years of the Cretaceous. These replaced the older sediments that got eroded away. Only few patches of these sediments exist in the NE corner of the county in the mountains. Older volcanic rocks, that are related to andesitic subduction volcanism, can be found at the western edge of the batholith.
EXAMPLES: Black Mt., San Miguel Mt. near Chula Vista, Double Peak near Excondido, Otay Mt., Fortuna Mt./State Highway 52, Helix Highlands, Del Cerro Highlands.
Younger volcanism is related to the opening of the Gulf of California and only can be found in S.D. county
EXAMPLES: Table Mt. near Jacumba (incl. lava flows), the Volcanic Hills, Vallecito Mts. and Fish Creek in the desert; and a small dike off Scripps beach.

San Diego County Timeline

Ordovician500 Mio yr oldest sedimentary rocks; submarine environment
Triassic200 Mio yr Pangea breaks apart; sediments get exposed and eroded; S.D. area somewhere south of equator
Jurassic190-136 Mio yr subduction of the Farallon Plate (now gone); andesitic volcanism in Peninsular Ranges
Cretaceous136-65 Mio yr intrusion of batholith and uplift of Peninsular Ranges, creating metamorphic rocks (e.g. Julian Schist); andesitic volcanic rocks eroded as well as sedimentary rocks that are replaced by batholith
Tertiary(Miocene)17 Mio yr volcanism related to opening of Gulf of California; Baja now on Pacific Plate and moving north relative to North America

Cool Volcano Web Sites

Smithsonian Institute; this site describes volcanoes world wide, some in great detail (e.g. monitoring logs).

University of North Dakota and Oregon State University; this site describes volcanoes world wide, has cool pictures

Michigan Technological University; this site has useful links to other sites

Award-winning site at San Diego State University;

Visit a U.S. Geological Survey Observatory:
USGS Volcano Home Page
Alaska Volcano Observatory
Cascade Volcano Observatory
Hawaii Volcano Observatory
Long Valley Observatory
Yellowstone Observatory

Cool Links Found by Visitors

Goto SIO15/ERTH15 "Natural Disasters"

Gabi Laske (

Gabi's web site
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