NOTICE CONCERNING COPYRIGHT RESTRICTIONS
This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material.
The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material.
Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement.
This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law.
CHRONOLOGY OF ERUPTIONS IN CALIFORNIA
* DURING THE LAST 2,000 YEARS
Richard T. Kilbourne, Geologist California Division of Mines and Geology San Francisco, California
ABSTRACT lichenometry, palynology, tephrochronology, amino-acid racemination, thermolumines- The length of time since the latest cence, and electron spin resonance. Utiliza- eruption, along with the periodicity and tion of these dating methods will undoubted- temporal pattern of eruptions, is a useful ly add to the list of active volcanoes. tool in assessing the risk of future volcanic events. Using occurrence of an eruption in the latest 2,000 years as the definition for INTRODUCTION active volcanoes, California has at least 27 active vents with 93 dated ash- or The primary aim of this study was to lava-producing eruptions. Ten of these compile California's age-dated volcanic vents are in the Cascades; three are in the eruptions -- that is, gather age-dates -- to Mojave Desert; and the remaining 14 are in obtain a picture of eruption frequency and the Mono Basin-Long Valley region. eruption patterns in California. The time period of interest was the latest 2,000 years. Chronological data suggest that a peak eruptive period occurred in both the Cas- Definition of Active. In looking at the cades and Mono Basin provinces near the latest 2,000 years of volcanic activity in year A.D. 900 (+100). Smaller peaks of California, we are seeing the truly "active" activity are apparent in the Cascades for volcanoes. The term "active" is more of a the years A.D. 100 (+100) and A.D. 1750 lay than a scientific term, but it behooves (+100). On a scale of centuries, the us to use it when we speak of volcanic eruption-frequency pattern in California hazards because it is one for which the seems to follow a Poisson distribution. This public already has a general understanding. pattern suggests that future volcanism This conference has shown that communi- would occur as a major period of eruption, cation is essential for scientists to properly lasting perhaps more than a century, serve the public in predicting hazards. followed by centuries of decreasing activity until the next cycle is started. More data The term "active volcano" has been are needed before any periodicity for this defined in a recent edition of the American cycle can be established. Geological Institute Glossary (1980) as: "A volcano that is erupting, also, one that is Dating methods most useful in this study not now erupting but is expected to do so. are: dendrochronology, historic observation, There is no precise distinction between an Carbon-14, rate of formation of obsidian active and a dormant volcano." This hydration rinds, stratigraphic tephrochron- definition is imprecise and, as stated, and ology, and declination magnetostratigraphy. can be confused with dormant volcano, Other methods deserving wider application which has been defined as: "A volcano that for dating youthful volcanic events include: is not now erupting but that has done so
4-76977 29 within historic time and is considered likely these questions, they are usually from the to do so in the future." chronological records of its previous eruptive history. The author feels there is a need for a revision of the definition of the term Just as confirmation of the theories of "active volcano." As used in this article, continental drift and the astronomical and as I would propose its standardization theories of glaciation has been advanced (Kilbourne and Anderson, 1981 ): An active with age-dating, so too may age dating volcano is one that is now erupting or one someday enable us t& recognize a period- that is known to have erupted within the icity to volcanic eruptions. This would be a past 2,000 years. The term "potentially major breakthrough in the science of active volcano" is proposed to replace the volcanic predictions. term "dormant" and to represent a volcano that has erupted in the past two million Dating methods found to be most useful in years but that is not known to have erupted this compilation and listed in order of in the last 2,000 years. estimated reliability are: dendrochronology, historic observation, Carbon-14, rate of These definitions have the advantage of formation of obsidian hydration rinds, strat- being precise, mutually exclusive, and not igraphic tephrochronology, and declination overburdened with loosely defined concepts magnetostratigraphy. Other methods such such as "historic time" and "considered as lichenometry, palynology, amino-acid likely to erupt in the future." racemization, thermoluminescence, and electron spin resonance have the potential Uses of Age-Dating in Volcanology. The to date young volcanic eruptions but have usefulness of chronological studies of vol- not been used to date any of the specific canic eruptions lies primarily in volcanic eruptions compiled in this study. Volcanic eruption prediction. Simply stated as a events dated only by K-Ar methods or by modified converse of Hutton's principle of their general youthful appearance were not uniformitarianism: The past is a key to the added to the list. The margin of error in future. Probably nine of ten of the world's these methods is considered too great to eruptions this century were from volcanoes accurately date events of the past 2,000 that have previously erupted within the past years. 2,000 years. It is also reasonable to esti- mate that 99 of 100 volcanic eruptions this Correction Factors. Authors using century were from volcanoes that have various dating methods commonly use erupted in the last two million years. Age- diff erent notations of age ("years ago," dating of the products of eruption identifies 1776, B.P., etc.). For this study, all dates these active and potentially active have been adjusted to calendar years A.D. volcanoes. Uncertainties, if expressed in the original date, have been transferred to the A.D. Age-dating can also be used to discrim- date. Due to lapses in communication be- inate between volcanoes that erupt often tween this author and an original source of a from those that erupt seldom. The particular date, a correction factor may identification of Mount St. Helens as the have been incorrectly applied. The original most active of the Cascade volcanoes date source has been quoted verbatim so (Crandell and Mullineaux, 1978 ) was based that any such error(s) could be adjusted in primarily on age-dating and led to their the future. forecast that Mount St. Helens was likely to erupt before the end of the century. Radiocarbon dates have consistently involved the most "correction," so the Another use of age-dating in volcanology methods used will be detailed here. Before is to distinguish patterns of eruptions. When changing to calendar years, C-14 dates were a volcano erupts, does this mean it will be first standardized to B.P. (before 1950) followed closely by further eruptions? larger notation and the Libby half-life ( 5568 eruptions? smaller eruptions? eruptions of years). Ages were then corrected for the other volcanoes? When we have answers to atmospheric variation with time of C-14
30 levels according to the curves of Seuss California is not a single volcanic pro- ( 1970, 1979) and Stuiver ( 1978). This last vince. Study of temporal patterns of vol- mentioned step adjusts the dates to A.D. canism is most productive through the study calendar years and recorrects for the of individual tectonic regions. California's presently accepted half-life of C-14 ( 5730 Cascade Range is such a region. A years). At this point, a few radiocarbon histogram of dated volcanic eruptions for dates on wood were further adjusted for the the Cascades (see Christiansen, 1982, this annual rings to the outside ring (presumed volume) is presented in Figure 2. This year of death). histogram suggests three periods of relatively high volcanic activity in the Source of Error. Not all eruptions of the Cascade in the past 2,000 years. It also past 2,000 years are datable nor, in some suggests a Poisson distribution for eruptive cases, even identified by geologic study. events with major periods of activity Lava flows and ash falls in active volcanic followed by centuries of decreasing regions must bury and obscure earlier flows activity. It may be significant that, at least and ash falls. It is a reasonable estimate in the most recent two periods of high that perhaps 40 to 50 percent of the major volcanic activity ( 800-1000 A.D. and tephra eruptions during the first millennium 1600-1800 A.D.), all three of California's have been recognized, dated, and included in major Cascade volcanoes, Mt. Shasta, the count presented in this paper. For the Lassen Peak, and Medicine Lake Highlands, second millennium, we recognize perhaps 75 erupted. percent of the major events. These are estimates only. In the Mono Basin-Long Valley region, the Poisson distribution of eruptions (Figure 3 ) Another problem in deciphering a is even more evident, with only one peak complete volcanic history is that of erosion period of eruptive activity between and varied wind distribution of tephra. 800-1000 A.D. Because of the easy erodability of unconsolidated volcanic materials, and the The histogram of Figure 4 shows the lack of detailed study of such deposits on a frequency of eruptions, based upon the data statewide basis, it is logical to assume that from Table 1, for the entire State of Cal- the count of eruptions presented in this ifornia. Table 2 summarizes some statisti- paper represents mainly major eruptions. cal conclusions to be drawn from the The list of dated eruptions in California is regional and statewide eruption frequen- certainly incomplete and includes only cies. The average number of eruptions over larger eruptions that have left substantial the centuries, projected into the future, ash or lava deposits in locations that are serves to alert us that the hazard should not well exposed or that have been subject to be ignored in emergency planning. The detailed tephrostratigraphic study. statistical data is preliminary at this stage but stresses the importance of gathering more geotechnical data useful for specific RESULTS time and place predictions.
Tabulation of Eruptions. Table 1 is a com- In further study of recent regional vol- pilation of California's dated eruptions less canism in California, if a pattern emerges than 2,000 years old. It shows that we have that can be correlated with a causative had at least 93 volcanic eruptions from force or even one that simply establishes a some 27 active vents over the past two mil- predictable periodicity to eruptions, a sig- lennia. For the purpose of counting erup- nificant reduction in volcanic risk would be tions, each clearly distinguishable volcanic attained. With this objective, the California rock unit is considered a separate eruption. Division of Mines and Geology would The locations of prominent young volcanoes appreciate receiving any new data on the or vent areas are shown in Figure 1. age-dating of recent California eruptions.
31 ACTIVE VOLCANIC REGIONS OF small eruptions, affecting areas which are CALIFORNIA now mostly included in Lassen Peak Volcanic National Park. For the purpose of a comparative discussion, California can be divided into Lassen Peak and its two associated five active volcanic regions: Shasta, Lassen volcanoes probably represent the most Peak, Medicine Lake Highlands, Mono active region in California. Though most Basin-Long Valley, and Mojave Desert historic eruptions have been small, Lassen, (Figure 1 ). like its similar sized and active neighbor to the north, Mount St. Helens, is believed The Shasta region contains only one capable of much larger eruptions. A repeat documented active volcano, Hotlum Cone or eruption in this region could be expected Mt. Shasta itself. The record of the last within the next 100 years, but further study 2,000 years shows this large strato-volcano and geophysical monitoring is needed before to be capable of destructive explosive a forecast can be made. eruptions. Medicine Lake Highlands is one of the The most recent eruption occurred in least known of California's volcanic 1786. There are no good local eyewitness regions. More than 100 cinder cones, accounts, but the eruption was large enough domes, and lava flows are found in this to be seen by Captain La Perouse while region; most of the vents are parasitic to or sailing off the northern California coast superimposed on a large shield volcano. At (Finch, 1930). Miller (1980) describes and least four vents ( Table 1 ) are classified as documents pyroclastic flows and hot active (dated as erupting in the last 2,000 mudflows that appear to be associated with years). These include Glass Mountain, Little this most recent activity. Glass Mountian, High Hole Crater, and Cinder Butte. Heiken (1978) suggests that In planning for the next destructive its main volcanic center lies at the eruption of Mount Shasta, it is consistent intersection of several normal faults. As with the recent geologic record to expect a would be expected in a shield volcanic, most moderate to large explosive event similar in of the eruptive products are lava rather type to the most recent eruptions of Mount than pyroclastic. St. Helens. Shasta is larger than either and is presumably capable of large eruptions. It The earliest eruptions were mostly of is also reasonable to assume that such an fluid basaltic lava whereas the most recent event would occur within the next 200-300 eruptions were rhyolitic. This distinction is years. important in assessing volcanic hazards because rhyolitic magma tends to erupt The rare case of a Mt. Mazama or Mt. more explosively, producing ash and Tehama caldera-forming type eruption pumice. However, these recent rhyolitic (Christianson, 1982, this volume), though eruptions in the Medicine Lake Highlands possible because of Shasta's great size, have been small and relatively nonexplosive. seems too remote to warrant planning at this stage. This caldera-producing type of The most recent eruption in this area event has been documented as happening occurred at Glass Mountain in the spring of only once ( Mount Mazama eruption about 1910 (Finch, 1928). It was a very minor 7,000 B.P.) in the last 10,000 years for the eruption which, if it had not been witnessed, whole Cascade chain. would probably not be listed in Table 1.
The Lassen Peak region contains at least An earlier and larger 1750 event was a three volcanoes documented as active. fissure eruption producing a rhyolitic lava They are: Lassen Peak ( last eruption flow and eight lava domes. Interestingly, 1914-1921 ), Cinder Cone ( last eruption this 1750 eruption is believed to be recorded 1850-1851 ), and a dome near Chaos Crags in local Indian myths ( Kilbourne and ( last eruption 1854-1857). All of these and Anderson, 1981 ), and has been dated by most of the earlier eruptions from the Carbon-14 and obsidian hydration rind Lassen Peak region have been relatively methods. l
32 CALIFORNIA'S ACTIVE VOLCANOES
DATED AS ERUPTING WITHIN THE LAST TWO THOUSAND YEARS
Figure 1
1240 1226 420- 120° -1 -42 ° 1, SHASTA %t, MEDICINE LAKE .L 4 * HIGHLANDS 1 410- A-J«3 1 1 I r j LASSEN PEAK i 1 4,----»3, lin\ • ·,· -1 - 1 -4 C -400 -3 . 11 ----5 \\ '4.--- ill 9 ,-4 ' 6---»r« ..3.--''L-3 wt. ..1.7•-3. i- 61$-'i ( r. 2,\ 2 -4 /1. r\\ r-1 tr.»--4.-1, i 4 '. 1 /- />.'12 "\ • 1 -C•L*Fvf, A. '\ 380- (18# MONO BASIN-LONG VALLEY 2- 1 ....4 >d --3.,1>1' \ -3/ ( <' , 1,.P»-31 2-'' )4' J 1 \. 1170 370 \\ I 7 / \+ '4 4< 4%.-I _r-r--1 \\ I \ 47 h /(· \ 1160 '»-,4 f- i 7 \1 360+ - #$- 360 t./ i -.I.il - J. 122° -_.._1_------..US. t 1 h \\ LL, 1 MOJAVE DESERT * 3- 35, 35'A- rr-\-1 '' 121 ° 1-,4-3---/ * \ 1 \ * 120. J 1 > ..I- - --- 0--- 1--I- - --1-34. 340-•- 1190 I.<- .5 1 J 0 50 100 ------•.------7 1 SCALE IN MILES •- 330 330-•- I 0 -- " *- -R--.-1 --- -r-iIt 5° 1170 33 ...i.. 0I li. E : .-'(\J U0 0' 036...... '.-C .--",r--9.- . r- 3g «* I :- 0 -- 0 L r-r- > r- 0 U- 0.- '-' -0 CJ•R .r- g .5.- Z A C 0' . 5 :. B & 44 - - . •I- Ai M 40 Or-= - - SmE*=r = - = 42 9. - : 8 2.2 m = 9 : 5 ES E -0 -.LO * Cl. E 2" f - Fi i C -0 0 - - -.1 3 E• 154 f 0 a' LO . 3 - NE=•ESS -* c-•-- I =: •: i •(/) .-Il.. 442 2. 9 - -«--.Ln - -• SzoE-•«..---"v E --I.. f ;E .- :3 -8. --1 i« - 4429.- . r-Crt - U Ln00 -r- 0-- U ...0 -On . -a 8 m: +re -0. r-Inro - .--; r---c--"- 9.'. 9 --0- 4- %-C- I" -7 .0+J= N -3 F •'0 28 1: 3 . .0 . I «'=- Q u •EZ g In . U I ./ -» -7 .i Onf U - 9 . - 9 -»52 *- . -.7 39 :.- e & 22:r#35 -«" -I-Ill •i- r.ch " u Cri - 9 •2 ...I »1 e.32 -i i= /6/. . . 4. -I -C}-r--"0 .13.3-0- --I >• -- - - . 9 - = - - :. - - --».....- •1- 9... - E.-l=-0- - ur 7.CO -9I - Z.-... i• *- 3 ;2 - U 5 2 -°.-.-S 5 :2 2 5 --00CIO=..Co U := --.c' - : & - Y /1 1% 3 2. 5:-C"" - -c - . - 9 - 9' '0 - 30 g » = * 0 I. * 0 4- -0 0 5 ZoZ- 0%• - 5 0366 - LL. : CS --m- = .- - 036 U 5 g.:pic: 5 2 8- 2 - 5 2 2 im: 2 »C >.C+J- . -I -* E 3.E :: 2 r ./ 2 .at i f 9 . .. . . » I.-- . • 490 -I- •*A• • •52 - •; • 0 5 5 8. = B "S. • • 2-=23/EX 2 -- - - 9 5 28 E:g S ME "- i 0 0 0 U. U : 0360=& 0 -%--- .- 0 -Or-r- 0- - & 72 :.0 0 :>, I f 036+, +, -00 0 •:0 5- I.0 ..=- 9 5 2•-*85254t§ *EE 2-• • •i m •f 137 E :3 gf 2 2 u . 0 -O U . 3/- u 5 5::25*£4 55-58-5 01 , - ..0 9 I. «,*-042e - 036%-- 2 •-s*.ti- 0 0*J+J -- 0 -.. 9 -. -,036/W SS..S .,09 *0 »: :0*....: 45 :=: 4 2: 41 4 4 ... I r 036-.... = •I -wl--*.---I -C.. 0C 4:.0:.CE-0 r-•:r 4C - -. .036. I . . -= •ma' I.-r- 01 I-r- -.I. -r I- «-09... I- & 85.=5:52 0 085 60 0 6 9,0...CO0.-0 e gE UE,. u u g 3 gn. 0 -C 9 - CU 4 : C K .' : 9 -I . . 0 -/ -0 036-.-J = > L - i i 0 C . a. . + 0 0 28 6 - E 5 Z -0.- "r- - >' -0 . 3 4= -=- - L -0 LU . E 0 LI . F>b ..C UDC 0(U : 0 ·'0 0. S= « ril- .. -0 .C r-1 L f 1/7 X « -> 036/ C •3 E >0 0C . . 4·h. . CO : - 0.--= E . > ,- Av . ANEEI E 036 0 8 8 0% : 3 2- Ng. Ear E- 0 C I C C 8 2.:: •o• 22 E2 4- - 0 : -0 - g . 3 82 3 > E254i:i g 2 me- .: 2 -C11 E 0 U 0 0 . 0 . ri . r.. 0. 8 . E-1 = 4 '- -C,0 = . .- fl r ::2 4- » -Ily-. CL- ri. ; 2 r. a.D . - . . . . . ;: . lilI- . e . Cl. . 2- 5 '0 = L = . «= 0 > -C XI . 0 (11 . ·C -LU • ° 5 : w 33M :2 4 /00 -Cl . : 4'> i 5 : • : »« =036 . . J - 0- - . 0 " 2 r - G - » U . = Ur- t : . » s BB •• r ;SE = - ... 036- 036 =- " " . a I --0 i % -.036--- 0. : i.22 E SE 83 53 &2 8 W.-3-W U f jj if • • -• •• CD -3 4- L Ek 3 -... - « LX « «= «.
.C •L *' U C C. 0 : .036 % C . -* = = E- JC> - = .C = 6 . 3 2 - Z r J 3 2: '0 . U '036a. 5 - 0- "- a-- -. 2/5 C. +-0 . . . - 2 4 L O L . U : -1 65 -• C »' I I " 85036. -. 5 25435% 9 3 0 ./ : 2 .- .= C & . E 0 : g .' . U f E a i fl 3 F » -9 *2 3 G g -:/ 2 U 0 . LC U 10 . - ..>5 .3 . L & 1 im E C CU 5- £ . C . 0 -6=S'. .fe 5 :0 (11 0 1 4 C -C E • =500362 *- 3 5 /2:: 3 I 036 0 C . C 0 C .Ln • 1 5 3# 1 8 10 . /4 4 - 5 g 2 :254I 22: 8 G U 3. 32: U 2 U .0 - =: S= & 3. 341 -'U 0I : 2 . : I : U fi -- 51 1 2 SES 55 m H h 2 i L - -=. c. 8 5 5 ii i W . . rn .... gl a 3 GE =3 t: 02 3 1 COI-- 0 UU=-C --I% U I0 >0 4-:-r- ZI U·- U.L -C Z0 •0 0.
g 9 Z- .e «' • tO m g: 0 3% : 2 880.•0 5 =- * . .- 0 •-0-a.0042 0 0Ch 0 2 3 6 eg C" Ch CO CO CO ,- r• ma•0 Eto •035•0 # 304 $5Ln 5 NE•cr r, SES - - -
34 1 I. ". 9 -- -" .5 400 C '::. 9 = C ro - 10i 9+ * . 9 « A-: 0 22 gS . 0 . -...... 1- 2 g =.>, 4, ".. . +J- i '«- *= ..f W . -10 . .E036*9036r-- =-0 • . -0- .0 -" CLI I - -- 036- SSES El R 'ng- := :: ..-.-- • •0 32 •BSE Z :: 2 ... 2 372549: 9'* C,-0 ./ C *:-.. fc Cn 9-- ./- -...0 ..0.9 -. .... - - -- =-. ... .- - - -0360 4- 01 CO .0-ie co. .5 9== 8, 1, 0 " • : 8 .0 9. E 0, (nue Cm. :A cri0 & &-3 . L - 3- C =..--+ --9- 08 (=29A '. --.C' - =.--e -0 . U 2: 1 E .= - ... . I - 9 9.-9 - - . I Ii.9 - - - A . - - -. * .=C . r +-C 0 -'r-•O 9..«' -C . -O - " . . 1/' -00 . - ... .0.. m ( 5254:56.m : 4 -. 9-.9, •9... 9C S.- al 0 CU •=r - 9 * E 2 ••••B 8• k :E 3 93 - »., - .H -1 I1.0 - :: 2-2. 2 Or- 5• --a n I-. . -0 -r- 0 L » 3 . u :=:I036m 1-- - ... .= 5 -*84 c c"I r\- r.-.- -1- :8 68 55 . 0-CO 21 ./C =.- « 9 - .(DC •I I. 9- . . .9 • % rn : 2 --0-C 9 e -0 U " r- 442=. I .-0 - . ..1 . . 99 22 b 93:2 6- •00 & 0:3 : 50 - 010 g 2036.9.036•k 22 4oom c 9 ...... = - 2N '-'e•.0.- 2. I. . I. . 59 : : 8:1 EE . +, fe - =- .- : rn . A * -
35 DATED CALIFORNIA VOLCANIC ERUPTIONS CASCADES AND MODOC PLATEAU
-15
-10 NUMBER PER 200 YEAR -5 PERIOD
0 0 400 800 1200 1600. 11981 YEAR A.D.
Figure 2
DATED CALIFORNIA VOLCANIC ERUPTIONS MONO BASIN-LONG VALLEY
-15
- 10 NUMBER PER 200 YEAR -LL -5 PERIOD
»rl 1 0 0 ' 460 ' 800 i260 ' 1660 1981 YEAR A.D.
Figure 3
-25
-20
-15 NUMBER PER 200 YEAR 10 PERIOD
-5 L 0 0 400 ' 800 • 1260 ' 1660 ' 1981 YEAR A D. DATED VOLCANIC ERUPTIONS-CALIFORNIA
Figure 4
36 Table 2. Simple statistical predictions - volcanic eruptions in California for the next oentury.
Region Pattern Eruptions/Century
Actual Average Factored Average Visual Extra- dated eruptions polation of past 2000 years past 2000 years* frequency histogram of next century
Mono Poisson 1.85 2.77 1.5 Cascades Poisson 2.55 3.77 1.75 All California Poisson? 4.4 5.54 3.3
* Assuming eruptive frequency has been progressively obscurred, the following factors (multipliers) were used to compensate for this presumed loss of data: 0-200 A.D. x 2.5; 200-400 A.D. x 2.25; 400-600 A.D. x 2.0; 600-800 A.D. x 1.75; 800-1000 A. D. x 1.5; 1000-1200 A.D. x 1.45; 1200-1400 A.D. x 1.35; 1400-1600 A.D. x 1.25; 1600-1800 A.D. x 1.15; and 1800-1981 x 1.0.
37 Based on the chronology and types of past The youngest dome in the Cima volcanic eruptions, future activity in the Medicine field is the only vent presently documented Lake Highlands might be small eruptions of as active ( last eruption about 1500 or 1650, ash and pumice tephra, perhaps a lava flow see Table 1 and Katz and Boettcher, 1980). or cinder cone, but probably not explosive or The region as a whole contains several far-reaching in their impact. Glass young basaltic lava flows and cinder cones Mountain, a historically active site, and the of undetermined age. As with earlier seismically active area around the town of eruptions, future activity is likely to be Tennant and Stephens Pass would appear to outpourings of lava and construction of be likely sites for future eruptions in the cinder cones -- not a particularly hazardous regions as suggested by Christiansen ( 1982, type of eruption in a sparsely populated area. this volume).
The Mono Basin-Long Valley region, which ( DISCUSSION follows the Christiansen has recently been the site of unusual paper.) earthquake activity and seismic swarms ( Sherburne, 1980), contains a chain of more than a dozen active craters and domes. At REFERENCES least 30 eruptions have been dated as occurring in the last 1,981 years ( Wood, American Geological Institute ( AGI), 1980, 1977; Kilbourne and others, 1980). The Glossary of Geology, 805 p. latest eruption was a minor phreatic explosion occurring in 1890. It is Bailey, R.A., 1982, The Long Valley-Mono, documented only by a single newspaper Coso, and Clear Lake volcanic fields, in report describing the unique phenomena that this volume. would be associated with a sublacustral ( Mono Lake) volcanic explosion. Brewer, W.H., 1930, Up and down in Cali- fornia: Yale University Press, p.458-66. The Mono Basin-Long Valley region was first studied in detail by Russell ( 1889). It Chesterman, C.W., 1955, Age of the obsid- has long been recognized as an area of ian flow at Glass Mountain, Siskiyou recent volcanism and spectacularly scenic County, California: American Journal of volcanic landforms. Most of the domes and Science, v. 253, p. 418-424. coulees (viscous lava flows with blocky, steep-fronted form ) are rhyolitic. This Christiansen, R.L., 1982, Volcanic hazards region is quite removed from the plate in the California Cascades: Mt. Shasta, boundary tectonics of the Cascade Range Medicine Lake Highland, and Lassen Park, and is one of two active intracontinental in this volume. volcanic vent areas in the United States ( San Francisco volcanoes in Arizona being Crandell, D.R., Mullineaux, D.R., 'Sigafoos, the other). R.S., and Rubin, M., 1974, Chaos Crags eruptions and rockfall-avalances, Lassen The mechanism for eruption (Kilbourne Volcanic National Park, California: and others, 1980) in this region may include Journal of Research of the U.S. large earthquakes and earthquake swarms Geological Survey, v. 2, n. 1, p. 49-60. that open fractures through which lava begins rising to the surface. Such swarms Crandell, D.R., and Mullineaux, D.R., 1978, have been associated with other rhyolitic Potential hazards from future eruptions volcanoes ( Minakami, 1974). The author of Mt. St. Helens volcano, Washington: agrees with Bailey's ( 1982, this volume) U.S. Geological Survey Bulletin 1383-C, recent assessment that this region has a 26 p. high potential for eruption within the next 50 years. Day, A.L., and Allen, E.T., 1925, The vol- canic activity and hot springs of Lassen The Mojave Desert appears to be the least Peak (California): Carnegie Institute active of the five named volcanic regions. Washington Publication 360,190 p.
38 Finch, R.H., 1928, Lassen Report No. 14: Division of Mines and Geology, Special The Volcano Letter, n. 161, p. 1. Report 150, p. 7-22.
Finch, R.H., 1930, Activity of a California Kilbourne, R.T., and Anderson, C.A., 1981, volcano in 1786: The Volcano Letter, Volcanic history and "active" volcanism in n. 308, p. 1. California: California Geology, v. 34, n. 8, p. 159-168. Finch, R.H., 1937, A tree ring calendar for dating volcanic events, Cinder Cone, Las- Loomis, B.F., 1926, Pictorial history of sen National Park, California: American Lassen volcano, 108 p. Journal of Science, v. 33, p. 140-146. Malone, S., 1982, The Mount St. Helens Friedman, I., 1968, Hydration rind dated Eruptions: Seismic monitoring for rhyolite flows: Science, v. 159, February eruption prediction, ill this volu me. 23, p. 878-880. Miller, C.D., 1980, Potential hazards from Harkness, H.W., 1875, A Recent Volcano in future eruptions in the vicinity of Mount Plumas County: Proceedings of the Cali- Shasta volcano, northern California: U.S. fornia Academy of Sciences, v. V, p. Geological Survey Bulletin 1503,1980. 409-412. Powers, Howard A., 1932, The lavas of the Heath, J.P., 1960, Repeated avalanches at Modoc Lava Bed quadrangle, California: Chaos Jumbles, Lassen Volcanic National The American Mineralogist, v. 17, n. 7, p. Park: American Journal of Science, 253-284. v. 258, n. 10, p. 744-751. Russell, C., 1889, Quaternary history of Heiken, G., 1978, Plinian-type eruptions in Mono Valley, California: U.S. Geological the Medicine Lake Highlands, California, Survey, Eighth Annual Report, Part 1, and the nature of the underlying magma: p. 1-495. Journal of Volcanology and Geothermal Research, v. 4, p. 375-402. Seuss, H.E., 1970, Radiocarbon Variation and Absolute Chronology: Proceedings of Ives, P.C., Levin, B., Robinson, R.D., Rubin, the 12th Nobel Symposium, 01sson, M., 1964, U.S. Geological Survey Radio- editor, Stockholm, Almquist and Wiksell, carbon Dates VII: Radiocarbon, v. 6, p. 595-605. p. 37-76. Seuss, H.E., 1979, A calibration table for James, D.E., 1966, Geology and rock conventional radiocarbon dates, in magnetism of Cinder Cone lava flows, Proceedings of the Ninth International Lassen Volcanic National Park, Cali- Conference on Radiocarbon Dating, Los fornia: Geological Society of America Angeles and La Jolla, p. 777-784. Bulletin, v. 77, p. 303-312. Stuives, M., 1978, Radiocarbon timescale Katz, M., and Boettcher, A., 1980, The tested against magnetic and other dating Cima Volcanic Field, 1!1 Fife, D.L., and methods Nature, v. 273, p. 271-274. Brown, A.R., editors, Geology and mineral wealth of the California Desert: South Townley, S.D., and Allen, M.W., 1939, Des- Coast Geological Society, p. 236-241. criptive catalog of earthquakes of the Pacific Coast of the United States, 1769 Kilbourne, R.T., Chesterman, C.W., and to 1928: Bulletin of the Seismological Wood, S.H., 1980, Recent volcanism in the Society of America, v. 29, no. 1, p. 1-297. Mono Basin-Long Valley region of Mono County, California, in Sherburne, R.W., Wood, S.H., 1977a, Distribution, correlation, editor, 1980, Mammoth Lakes, California and radiocarbon dating of late Holocene earthquakes of May 1980: California tephra, Mono and Inyo craters, eastern
1 39 California: Geological Society of U.S. Geological Survey, Contract America Bulletin, v. 88, p. 89-95. no. 14-08-0001-15166,77 p.
Wood, Spencer H., 1977b, Chronology of late Wood, S.H., and Brooks, R., 1979, Panum Pleistocene and Holocene volcanics, Long Crater dated 640-40 years, B.P., Mono Valley and Mono Basin geothermal areas, Craters, California: Geological Society of eastern California: Final Technical America, Abstract with Programs, v. 11, Report, March 1977, sponsored by the no. 7, p. 543.
40