Ca Geology Chp 5

Front 1

What are the three main areas of recent major volcanic activity in CA?

Back 1

Cascade Province (Part of the Cascade Range)

The Modoc Plateau

Long Valley Caldera/area

Front 2

___ is an 800 km/500 miles chain of young volcanic mountains that reach from British Columbia to northernmost part of CA. Called the __ in CA. Geography in CA is more similar to its Northern geography parts. Of the 12 major volcanic cones, ___ is the second highest (behind Washington's Mt. Rainer) and the largest in volume. The other large cone in CA is ___, (last erupted between 1914 and 1921). Both summits are covered with snow and slopes forested. These volcanoes are made because of the active subduction of the ___ and ___ plates. Rocks formed by eruptions from chain during last 3 million years known as High Cascades series while older rocks predating the cones are known as Western Cascades Series

Back 2

Cascade Range;

CA's Cascades Province;

Mt. Shasta

Lassen Peak;

Gorda and Juan de Fuca Plates;

Front 3

___ is a high relatively flat country cut by valleys. Arid because high ranges block Pacific storms. Made up of young volcanic rocks. Less explosive than Cascades. Mainly lava flows like Lava beds.

Back 3

Modoc Plateau

Front 4

Kilauea simply flows that can destroy stuff but evacuations protect most. __ 1980 Washington killed 60 (would have been more if not evacuated) Geologist killed. 2 million cubic meters of ash had to be removed from highways. Cost 1.1 billion even though considered small. ___ 1991 Phillipines 5-7 cubic km of debris (last was 1 km). Killed 350 people, 2 U.S. air bases, thousands homeless.

Back 4

Mt. St. Helen;

My. Pinatubo

Front 5

Differences in the violence of volcanic eruptions can be explained by the ___ of the ___ feeding the volcano. By sampling and analyzing molten lava & volcanic rocks, geologists can determine the chemical composition of magmas.

Back 5

Chemistry of the magma;

Front 6

Although their chemistry is highly variable, lavas can be grouped into three broad categories. In all three, silica is the predominant component. Name them.

Back 6

Mafic (basaltic)

Intermediate (andesitic)

Silicic (felsic)

Front 7

Lava. Less silica (50%), high iron and magnesium (15%-20%). 90% of all the lava erupted worldwide is this type. Very fluid because iron and magnesium keep the silica molecules separated which prevents clumping. Move fast. Low in gas. Produces relatively well-behaved lava flows and fountains. Predictable. Makes what type of volcanic rock?

Back 7

Mafic (basaltic) lava;

Basalt (dark in color)

Front 8

Lava. Has a silica & iron-magneisum content that is in middle. Sluggish viscous clumpy flows. High in gas. Gets stuck in volcanic vent because of its high viscosity. Makes eruptions explosive maybe devastating. Unpredictable because stuck in vent. Makes what type of volcanic rock?

Back 8

Intermediate (Andesitic) lava;

Andesite (gray or brown in color)

(Mt. St. Helens & Mt. Pinatubo fed by intermediate to silcic magma and both violent)

Front 9

Lava. High silica (70%) and low in iron and magnesium. Sluggish High viscous clumpy flows because silica molecules tend to clump together or polymerize, even though the lava is still a fluid. Very High in gas (mostly steam and carbon dioxide). Makes eruptions explosive maybe devastating. Unpredictable because stuck in vent. Makes what type of volcanic rock?

Back 9

Silcic (felsic) lava;

Rhyolite, but can make volcanic glass obsidian if lava cools too quickly to crystallize.

Front 10

Chains of active volcanoes are concentrated near plate boundaries. Volcanoes occur at both ___ and ___. Some volcanic centers, like Hawaiian chain or Yellowstone volcanic area found within plates because they are over __ in the mantle. "Ring of Fire" is mostly __ composition (named after Andes mountains there). These are associated with active ___, some between O-C plates and others O-O plates.

Back 10

Divergent boundaries and subduction zones;

hot spots; intermediate/andesitic;

subduction zones;

Front 11

__ is a necessary ingredient for the production of andesite. Acts like a catalyst, lowering the melting temperature of minerals to enable partial melting in the portion of the mantle that overlies the subducting plate.

Back 11

Water

Front 12

__ magma rises at divergent boundaries & at zones where the crust is being extended within plates. Here, magma is generated by partial melting of the mantle beneath Earth's crust. Magma rises relatively rapidly along pathways created as the crust is stretched. Less dense & fluid so rises freely to surface.

Back 12

Mafic

Front 13

Volcanoes erupting only silicic lavas are found only within ___. Thought to originate from partial melting of continental crustal rocks rich in silica as magma rises from beneath the crust. High viscosity makes it rise very slowly and cool beneath surface to form plutonic rocks. Silicic lavas are less common than mafic & intermediate.

Back 13

continental plates

Front 14

Some volcanoes, Medicine lake in Casacades & Coso volcanic field in Sierra Nevada, produce both __ & __ eruptions. Rising basaltic magam can heat adjacent to crustal rocks & partially melt them to form silicic magma. Basalt can form directly from sources in the mantle. Result is volcanic area that contains both basalt and rhyolite of same age but different source magmas. Important: almost infinite variety of lavas is possible, considering the diverse types of rock that can be partially melted & the possibilities for mixing of different magmas.

Back 14

mafic and silicic;

Front 15

Geologists can use the lava & young rocks found at a locality as a clue to the tectonic setting of the area.

Cascade Province = intermediate subduction zone setting.

Modoc Plateau = mafic crustal extension

Long Valley = extension silicic lavas produced as basaltic magma rises into a more easily melted section melting & mixing to form silicic magma.

Back 15

You're a Bird dog

Front 16

___ are the most common product of basaltic volcanic eruptions. Can erupt from central or from a __ or crack along the flanks of the volcano. Lava fountains/curtains common in Hawaii. Streams can flow continuously in channel for hours or days.

Back 16

Lava flows; fissure

Front 17

Although basaltic flows less explosive than others, some more explosive events can occur. Most common product of more explosive eruptions from basaltic cones is __ or ___, which are porous fragments, pebble-sized or larger, thrown from the volcano. Fragments have frothy appearance because of abundance of __, or bubbles left by escaping gas.

Back 17

scoria or cinders;

vesicles

Front 18

Over a period of centuries or more, repeated eruptions of mafic lava from a central vent can create a __ like Medicine Lake. Broad and gentle sloping. Repeated eruptions along fissures can create broad plateaus of lava like Lake Beds rather than a cone. ___ are common features of all active volcanic terrains. Usually small cones, composed of fragments thrown from a central vent. After eruption, a funnel-shaped crater remains at the peak of the cone. Small ___, formed when blobs of lava are thrown from a vent and then fall in heaps, are also typical features of basaltic volcanic terrains.

Back 18

Shield volcano;

Cinder cones;

splatter cones;

Front 19

During large eruption of andesitic volcano, huge volumes of gas & instantly chilled volcanic glass released, along with chunks of rock from volcano itself. An explosive eruption produces wide variety of ___ materials, or fragmented debris produced by fire. Clouds of steam carbon dioxide asphyxiate people like Pompeii. __ material carried into the atmosphere is called __. Much of this is small particles known as ___, but some fragments known as ___ are centimeters in size and others known as ___ are half-meter or more. When gas trapped in vent is violently separated from lava, __ is produced which is a light volcanic glass with holes and can be carried long distances.

Back 19

pyroclastic materials; Pyroclastic materials;

tephra; volcanic ash; lapilli; volcanic bombs;

pumice;

Front 20

Flows can glow from incandescent lava fragments. These deadly avalanches known as glowing clouds or ___. ____ can be hot enough to partly weld the fragments within them. When they or volcanic ash are lithified to form rocks, they are referred to as ___.

Back 20

nuee ardente; pyroclastic flows;

tuff;

Front 21

Among the most deadly hazards during a large eruption of an andesitic volcano are ___. Eruption instantly melts the snow and ice on flanks, mixing in huge amounts of ash & debris, & sends saturated mixture down the steep sides of the mountain at incredible speeds. Disastrous, raises river levels, filling channels with debris.

Back 21

volcanic debris flows

Front 22

Over a period of several thousand years, eruptions of intermediate lava can form a huge volcanic mountain known as a ___ or ___. Summit craters & steep symmetrical sides. Shape reflects that it is composed of viscous pyroclastic material as well as lava flows. Can be partly or completely destroyed by catastrophic eruption. Ex. Oregon Volcano Mt. Mazama. Many eruptions & after magma was removed from vent, top collapsed to form depression.

Back 22

Stratovolcano or Composite Cone

Front 23

A circular depression formed by the collapse of an area above a volcanic vent. Centers might undergo cycle of volcano building & destruction, with new cones occupying the site of a destroyed mountain. Ex. Mt. St. Helens blown away in 1980, and since then, a new dome called a ___ is being built in the summit crater.

Back 23

Caldera; resurgent dome

Front 24

Silicic lava similar to andesitic eruptions. Explosive lots of debris. Rhyolite pumice, tephra, ash flows. Commonly produce ____ and glass flows. Because high-silica lava is thick & pasty, oozes slowly from vents and does not travel far before solidifies. Generally steep-sided.

Back 24

obsidian domes (Ex. Medicine Lake volcano & Mono-Inyo volcanic chain.

Front 25

__ is a stratovolcano built by eruptions from four main volcanic vents. More than 100,000 years to construct. Andesitic, pyroclastic, and debris flows, but few deposits of ash. Avg. interval between eruptions 600. 13 in last 10,000. Two eruption centers have been very active in the last 10,000 yrs. What are they? Glaciers that were present until 15,000 yrs ago eroded the two older cones. No evidence of glaciation in new ones.

Back 25

Mt. Shasta;

Hotlum Cone and Shastina Cone (composed of dacit domes a material w/ between andesite & rhyolite).

Front 26

Within the uplifted plateau lies ___, a recently active shield volcano between Cascades & Modoc Plateau Provinces. Excellent place to view results of basaltic to silicic volcanic eruptions. Many volcanic features formed within past few thousand years, & youngest flows too place no few than hundred years ago. Cinder cones, explosion pits, splatter cones found near vents. High on slopes of volcano are younger & more silca-rock rocks. Glass mountain & Little Glass Mountain source for tools & trade materials used by Modoc Indians. Youngest basalt flow at Mammoth Crater less than 100 yrs old. Greater volume than Mt. Shasta.

Back 26

Medicine Lake volcano;

Front 27

To the north of Medicine Lake lies the bare, flat, but rough-surfaced country of ___. This is a land of dark basalt flows, sparsely vegetated due to the desert climate. Famous for its network of tunnels & caves. Tunnels are ___, some of which carried mafic lava from vents. As fluid lava streams along a channel, a solid crust or roof might form on the surface and sides of these channels, because the outer surfaces cool more rapidly. Lava can drain out. Many roofs of tubes have collapsed providing access to tunnels.

Back 27

Lava Beds National Monument;

lava tubes

Hint 27

Last major war between U.S. & Natives fought in Modoc Plateau 1800s. 150 Modoc Indians VS 650 U.S. troops. Natives eluded them for 7 months by taking advantage of volcanic terrain and escape routes. Only captured after betrayed by fellow Modocs.

Front 28

Memorial Day May 30th 1914, Ike McKenzie of Chester witnessed huge cloud of steam from ___, signaling the beginning of the 1st volcanic eruption in the U.S. since the 48 states united. Not much people there. 1914-1921. People only died cuz went to look at it on top. Spring 1915 lava flow, debris flow, devastated area destroying trees. Today, hot springs & ___, areas where volcanic gas & steam boil from vents, reminds visitors of the recency of volcanic activity here. Geologist discovered eruptions were minor events (catastrophic in past).

Back 28

Lassen Peak;

fumaroles

Front 29

Lassen Peak itself is a plug dome of dacite that rose on the eastern flank of a huge hole created by a very large blast about 200,000 years ago. Almost destroyed large stratovolcano near it named ___. 2 other big eruptions too. One sent a lot of Rockland ash and was worse than eruption of Mt. Mazama. Other occurred 3.4 million yrs ago that sent ash flow down Sacramento Valley. Rhyolite flows w/ pumice. Today found as volcanic tuff named Nomlaki tuff.

Back 29

Mt. Tehema aka Brokeoff Mountain

Front 30

Mafic and andesitic flows began but then silicic domes & flows. Series of high silica eruptions began near Mono Glass Mt. resulting in series of domes & flows by ash and ash flows. Change in lava chemistry occurred as a large fairly shallow magma chamber developed beneath ___. Eventually, roof ruptured causing catastrophic eruption of rhyolite magma. Ash blown high in air extended very far Kansas. Deposits from the eruption are known as ___. The sudden emptying of the magma chamber caused the ground above it to collapse, forming an oval depression called ___. Eruptions still continue w/ pyroclastic & obsidian flows creating a ___ (rising at rate of 2/3 cm a year). Quiet period, but erupted again. No eruptions last 100,000 years, but magma still there and unrest. seismic activity occurred in 80s, but nothing happened.

Back 30

Long Valley; Bishop tuff;

Long Valley Caldera;

resurgent dome

Hint 30

Carbon dioxide leaked killing many trees. Numerous hot springs suggest magma is present beneath the surface.

Front 31

The __ is a system of vents 45km long that overlap with the Long Valley Caldera. Chain is linear & activity might be controlled by a fault in the underlying rocks. More recent activity than most of Long Valley eruptions. Highly viscous lava slow & steep front edges. Obsidian flows striking features of this. Many rhyolite domes, flows.

Back 31

Mono-Inyo Volcanic Chain (Mono Craters chain)

Front 32

Each eruptive source has a distinctive chemistry, ashes erupted from each source show slight variations in composition even from the same volcano individually different. When eruption occurs, composition of the lava remaining in the magma chamber changes slightly. Over time, the magma chemistry can also change because new molten material is produced.

Back 32

Because instantaneously cooled, glass gives geologists a particularly accurate look at the chemistry of lava at the time of the eruption. Each ash has a unique chemical "fingerprint". Used to trace source, size of eruption, history, frequency (recurrence interval), correlating sediments by radio metric methods. Good marker bed.

Front 33

1980s Long Valley Caldera thousands of small to moderate earthquakes occurring at fairly regular intervals, a pattern known as ___. Thought it was gonna erupt but didn't. Monitoring programs all volcanic areas. Examining dating volcanic deposits to predict. ___ are prepared for each area outlining the areas likely to be impacted by future volcanic events.

Back 33

harmonic earthquakes;

volcanic hazards maps;

Front 34

Materials mined for commerical use. Volcanic cinders are reddened fragments of basalt thrown from volcanic vent & often piled up into cinder cones. Used as base material for roads & railroad beds, decorative rocks, lightweight concrete blocks. Pumice is aggregate in lightweight concrete & acoustical insulating materials, soap., soil conditioner. Volcanic ash base material in Ag pesticides or insecticides and ceramics. Obsidian traded by Natives and used as scapels. Hydrated glass is known as perlite used in aggregates for plaster & fire-resistant wallboard.

Back 34

Have you heard of God the Mother?

Front 35

Recent volcanic activity in the Modoc Plateau Province and in the Basin & Range Province is a result of crustal extension. Lavas erupted in these areas are both mafic & silicic. Medicine Lake Highlands is the major volcanic center in the Modoc Plateau Province, & basalt flows from this area have formed Lava Beds National Monument.

Back 35