Summer 1994

L I T E New Mexico Bureau

... . ~, ¯ , ° - of ~. ~ ¯ , Mines and Mineral ’ Resources ’. "i ’. ~"’" :I:’ ""L , , (NMBM&MR) ~:.~i,~.~,~. :.. A quarterly publication £or educatomand the pul)lic- contemporarygeological topics, issues and evenls EarthBriefs Quake Shakes "~’.,#~%}?:!i’-t:’q~-.-..’.~:g;~:s ",.’:".’,:.~<~’,,.-..,.%" :.-.:.,. ~ ’,,’-, :’.; /,Y:.. ,~." : .~. ~.. :~, :%" ~.~. .’i.~; .- ~:%% %;%%~’cRY.. ¯ ,’.., :; .".: :" Y’~/,; .L" :.". : !:.’.’.i’. ":/";’,;: >"i <:.. ~.,vi..:... :...: ...... :.....,,p.-,.~.i.L ~;.~, )u.,~..:..".’.."’...,.i~ :. ". ’.":’...... t ~,’ : ’...::;: :.::."T,:. :i’ .,.-’:..’"I.F::: ;,;%" Thermal Lakes ":~.,.,:;,.’~,.:.:"’. :: :. !: ’ i:. ’q:{-. :.?"-.-:, .~.k : ;’::L{;. :.. :~:.": :.";:.~:..%~.;!,!:! This year in Yellowstone ~. ~ National Park, scientists have had ¯ ":: :;i:i;-![:;~.i/i.:.ii/:;:i.~:..i:i,Lf/;;i :i L! Tf]:i :::/,: : }i::i::,;iii ~i i :/i:idi/,!:!:~i :i!:if" a renewed opportunity to study the relationship between seismic events and tho behavior of geysers. Geysers, or hot springs that erupt y.~ ~ii~,! :) .}!~,: ,..,::i) on an intermittent basis, are SUlaplied with steam or hot water from reservoirs inside the rock. These reservoirs consist of a plumbing system of fractures in the rock that convey hot ground water to geysers and hot springs. Changes in this plumbing, either by opening or closing of fractures, can change the flow of water to the geysers, affecting their eruption ,::.:.::-,..’.~, ~ . ~\~ILI,~ ~.... ii:1~ ~i."~::i;~i~’.:::. h; ’ ",i.i :" ." .i . :.1.:~.. :.:..:’,":![.:,:,,:;.::.I",.., patterns. Earthquakes, such as the i !..’...:...~. .., ~. ¯ :.1... ii....;...’.:.: I March 26, 199.4 quake that rattled the Norris Geyser Basin in Yellowstone, can disturb the plumbing under geysers, resulting . :,::"/4’.!4:: ’ .’~ ,/.’. ¯ k.~:~-~,,... ~ ..,:." I~ !,.";.;::’.’’:.’,"~:;:;~~ : ’ . ".,.’ ~. in changes in water temperatures .... ::: ; .... ,:,I;i:’::: .! :,.:,:t ," -..~ :. ~ ~’...... :. ~:"..-. :..," : and levels, and in the magnitudes and frequencies of geyser ~ ~" ,:.,~~. ,.,., ~... ~..,/:: ’C~:.’:"::7 ! ~ !:.. ,~ ~"’:b’.’:": ". "’i:’l eruptions. ~~ ’".!:.:):."..::::.:".:..L? :. ’"".:.::T"i::...... :.:.:: ilv ...i:i(:: After the March earthquake, measuring 4.6 on the Richter scale, several geysers in the park have altered their behavior. Monarch Geyser, which had been sleei~ing "1 told you to take a picture of the for 81 years, woke up grumpy and GEYSERat Yellowstone--not the GEEZER." threw rocks, mud, and water 15 feet into the air about once a day. In the early part of the century, ThisIssue: before its dormancy, Monarch would shoot water up to 200 feet ...... 7 ...... ~ ...... skyward, higher than most Old Earth BriefsDseismic shake-up Whoreally knows where stones come Faithful eruptions. causes geysers to wake up from?--thebattle of theboulder Following the same quake, Have you ever.wondered..J-Iow Earth- Current topics in Earth Science-- Ledge Geyser erupted after a 15- quakes are measured? highLites year period of dormancy. In contrast, Steamboat Geyser, the Ancient Lakes--A Tool for [inderstand- largest geyser in the world, which ing C!!matic Change sometimes erupts to a height of nearly 400 feet, showed signs of

New Mexico Bureau of Mines and Mineral Resources Lite Geology, Summer1994 reduced activity, and perhaps is heading for dormancy. Changes in geyser eruption patterns are common following an earthquake, and serve to illustrate that Yellowstone Park’s geyser regions are a dynamic and complex weave of thermal and geologic processes. A few scientists speculate that some geysers change their pattern of eruptions before earthquakes occur. If so, it might be possible to predict earthquakes using geyser behavior. This hypothesis is being tested by detailed monitoring of eruption behavior of a few geysers in Yellowstone. The outcome of the data Seismic Geyser evolved from a fumarole in 1963, spitting collection awaits more earthquakes. stones and killing trees with boiling water. The evidence from previous observations, however, is that the most noticeable changes in geyser behavior begin with earthquake shaking and changes in natural plumbing. The known geothermal areas in New Mexico may be affected by earthquakes as well. Although there are presently no geysers in the Jemez Mountains or the Lightning Dock geothermal areas, changes in amounts and temperatures of water from hot springs and hot wells ! are documented in both areas and the water is hot enough to flash into eruption-causing steam under the right conditions. Earthquakes could change the plumbing systems to the geothermal fields. Hot water moving to the surface along a number of faults in Castle Geyser cone in foreground, Giantess erupting Jemez Canyon has shifted through beyond Firehole river, Upper Geyser ~asin. geologic time to.its present location at Soda Dam. Remnants of previous travertine spring deposits along the canyon walls show where plumbing systems used to be active.

Sources Elston, W. E., Deal E. G., and Logsdon, M.J., Valles caidera hydrothermal system: Marler, D. M., and White, D. E., 1975,~ismic 1983, Geologyand geothermalwaters of Geological Society of Am,erica, Bulletin, v. 99, Geyserand its bearing on the origin and Lightning Dockregion, AnimasValley, and pp. 292-302. evolution of gey~rsand hot springs of Pyramid Mountains, Hidalgo county, New YellowstoneNational Park: Geological Haines, J., "GeyserShakeup": Bozeman Mexico: NewMexicoBureau o[ Mines and Societyof America,Bulletin, v. 86, MineralResources, Circular 177, 44 pp. Chronicle,issue h)r May24, 1994, Bozeman,Montana. pp. 740-759. Golf, E, and Shevenell,L., 1987,Travertine Milstein, M., "LargeGeyser goes to deposits of Soda Dam,New Mexico, and their Hutchinson,R., August3, 1994, personal communication,YellowstoneNational Park, Sleep":Billings Gazette,issue for implications for the age and evolutionof the May3, 1994, Billings, Montana. Yellowstone, Wyoming. --story by D. Loveand S. Welch

Summer1994, Life Geolo~,,y New Mexico Bureau of Mines and Mineral Resources Castle Geyserin steam phase

Lone Star Geyser

phok~s by David Love, Senior Envinmnu’ntal Ca’ol~gi~t, NMBM&MR

.New Mexico Bureau of Mines and Mineral Resources Life Geolo~*y, Summer 1994 Have you ever wondered...

...How Earthquakes arc destruction). The intensity scale used As an example of attenuation, note Measured? most often in North America, the that the 1886 earthquake in Charleston, Modified Mercalli intensity scale, was South Carolina (estimated magnitude Richard Aster developed by H.O. Woodand E 7.2) was felt over an area of Assistant Professorof Geophysics Neumannin the early 20t" century to fit approximately 8 million square New Mexico Tech construction conditions in California kilometers, while the ~imilarly-sized Virtually everyone has seen press (California buildings have appreciably 1989 LomaPrieta earthquake was felt releases describing earthquakes around different features than Eur(~peanones!). over only about ! million square the world where the size of the The intensity scalej despite its kilometers of California as a result of earthquake has been quoted as a simplicity, is still a useful seismological the more attenuating rocks of the west magnitude. What exactly does this, tool today, particularly as a standard coast. The clearest examples of refer to, and howdo scientists assess for assessing the size of historic resonance and amp!ification effects are and quantify the size of earthquakes? earthquakes. seen in cities: This is because many As we saw in a previous article in Isoseismal contours also maybe measurements of intensity can be made Lite Geology, almost all earthquakes are used to estimatethe location, depth, in a small region and because certain caused by sudden fault slip in the and size of an earthquake when no types of .soft soil that amplifyseismic brittle upper few hundred other data are available, as deeper disturbances, such as "reclaimed" kilometers of the Earth. As most wetlands, are common. earthquake faults do not break Recent examples of extreme the surface, most of what is local amplification include highly known about earthquakes is localized and very strong ground inferred from observations of motions observed in Mexico City seismic waves that propagate during the 1985 Mexico away from the earthquake source earthquake (in areas built on an region at depth and thus can be ancient lake bed), during’the 1989 recorded ~t or near the Earth’s LomaPrieta earthquake (in the surface. Marina District of San Francisco), The earliest semiquantitative and the 1994 Northridge method of assessing the size of earthquake (in parts of Santa earthquakes is the intensity scale, Monica,California). first developedby the British The most commonly quoted engineer Robert Mallet to assess measure of earthquake size is the the damage from a disastrous magnitude. The original 1857 earthquake io southern Italy. earthquake magnitude scale was The simple idea is to measure the developed by Charles Richter in intensity of shaking, as indicated Figure 1--Diagram showing isoseismal con- 1935 for California. If you want to impress your friends, here is a by different types of structural tours, surface ruptt/re, fault surface, focus, and damage. One can then plot on a epicenter. strict definition of the Richter mapthe intensity of shaking at Magnitude: different locations and contour The base 10 logarithmof the the data to obtain a set of curves events will generally affect a wider area maximumseismic-wave amplitude (in (isoseismal contours) that indicate with equal intensity. However,local microns,or one one-millionthof a approximately equal degrees of ground shaking is highly influenced by meter) recordedon a standard Wood- shaking (Fig. 1). An isoseismal contour near-surface and regional geology due Andersonseismograph at a distance of plot thus gives an estimate of the to attenuation (the rate at which seismic 100 kin from the epicenter, wherethe spatial distribution of shaking. A wave energy is converted into heat by standardseismograph consists of a 5 -twelve-point intensity scale was friction), resonance (local buildup grammass suspendedon a torsion wire subsequently devised by the Italian seismic wave amplitudes due to with optical recordingand geologist Giuseppi Mercalli in 1902, constructive interference), and electromagneticdamping. It has a where the degree of inferred shaking amplification (soft materials which periodof O.8 secondsand magnifies ranges from I (detectable only with propagat~e seismic waves more slowly groundmotion by a factor of 3000. sensitive seismic instruments called induce higher amplitudes to conserve Mathematically,the Richter, or local, seismometers) to XII (essentially total energy).

Summer1994, Lite Geology NewMexico Bureau of Mines and Mineral Resources magnitude is duration magnitude scale is routinely ¯ can be seen on seismograms recorded M = log 10 ( 3000u ,,,, used to assess the size of earthquakes in virtually anywhere on the Earth with L New Mexico by the New Mexico Tech suitably sensitive instruments. Each of where um,, is the r~aximumground Seismological Observatory. these waves has its own associated displacement in microns. The Richter magnitude was magnitude scale. Seismic body waves Because of the base 10 logarithm in developed as a rough measure of travel deep into the Earth’s mantle and the definition, each unit increase in earthquake size in California, whei’e even through its core before reaching a magnitudereflects a ten-fold increase in distances between earthquakes and particular station, while surface waves, ground motion. An increase of two seismographs are commonly not more travel near the Earth’s surface. At magnitude upits corresponds to a than a few 10s of km. Manyearthquakes teleseismic distances these two types ground motion increase of 102 or 100. around the world, however, occur in of waves can be quite distinct on The instrument calibration is such that remote regions such as under the. - seismograms, in contrast with the maximumseismogram amplitude oceans and are thus recorded only at seismograms recorded close to the expected from a Richter magnitude 5 teleseismic distances of 100s to 1000s of source, which are characteristically a earthquake 100 km away is about 100 km. more complicated superposition of mm(Fig. 2). This ~corresponds to Distant large earthquakes produce body waves and surface waves. maximumground motion of about 33 two basic types of seismic waves that Surface waves are commonlythe largest signals on a teleseismic record microns, which is about 1/1000 of an $ inch. The expected ground motion for a ¯ ~ [ bodywave because they spread out over the (2- dimensional) surface of the earth, magnitude 7, on the other hand, is 100 [ while body waves must spread out times greater (3300 microns or about 1/ j~ p [ ’ 10 of an inch) which can easily be felt bodywe~e " even 100 km away. ’l~’~ [L Figure 2--Seismogramsof local and Note that earthquake magnitudes can :l.m [ Ji. distantearthquakesshowingdifferences be zero or negative, as the maximum in duration, arrival times of different k. l.ll~ati., wavetypes, and amplitudes, a) ground displacement, u,~ of an m ~ M = 0 earthquake is 1/10 that of an ]1~[~q~w’r’’"’~~ seismogramrecording a local L earthquakein southernCalifornia 15 km M = 1 earthquake, and the ground [ "~ JumbleJumble ofof sur~moesurfece&&bodybody weveawaves L t [11]1 from epicenter,MD = 1.6; displacement from an ML = -1 ea, rfhquakeis just 1/100 that of an . (b)Seismogram’fromAdirondack, New M = 1 earthquake, and so on. , , [ .... York, recording a ~leseismic earthquake L 4,200kilometers awa)6 off the coast of Seismologists study earth~iul/kes 0 sI ~me2eco.o.~o~sbe0,nnm0o~,ueUe)25 spanningthe huge range of 11 ordersof northernCalifornia, Ml=6.7. magnitude (magnitudes from 1 approximately-2 to 8). eu~~e/eal /~/~’~ ~/1AIli t~" Despite its simplicity the Richter magnitude doesn’t do too bad a job of P[Ix~/wave. Ix~l~~ ~~filllllllll[lllllll~l" w.ve ~ UV~UUIIVl quantifying the relative size of earthquakes, particularly whenthere are manystations to provide i , , , i , . , ~ , , . i , , , i , , , i , , , i , , , , measurements to average over. 200 400 600 800 1000 1200 1400 1600 Another scale that is used to measure Tlme (eeconds from beginning of quake) earthquakes at local distances (typically less than 100 km)is the duration Table 1--Momentsand magnitudes of some famous earthquakes magnitude, which assesses how long the seismic waves rattle around in the surface wave average seismic moment crust of the Earth before they become magnitude area of fault amount of slip scalar moment magnitude indistinguishable from the background sM S(lenllth x width) U (m) Me iN-m) Mu, noise. Its formula is Northridge (1994) 6.6 , 20 km x 14 km 1.4 1.2 x 10I* 6.7 Md = logt0(d)+ q San Francisco (1906) 8.2 320 km x 15 km 4.0 6.0 x 102o 7.9 Alaska (1964) 8.5 500 km x 300 km whered is theduration in secondsand q 7.0 5.2 x 1022 9.1 Chile (1960) 8.3 800 km x 200 km 21.0 0.4 x 1023 9.6 dis a factorused to makeM approximatelyequal to ML. The

NewMexico Bureau of Mines and Mineral Resources Life Geology,. Summer1994 over the (3-dimensional) interior. big earthquakes and really big magnitude reported’ more frequently in Whenthinking about thes(two types earthquakes, as we’ll see. To obtain a your favorite newspaper, especially for of waves, imagine dropping astone more meaningful measure of large earthquakes. into a pond. Sound waves from the earthquake sources we must look more Because the seismic momentand the impact (which you don’t normally sense closely at the physics of fault slip. moment magnitude are determined by unless you are a fish) travel deep into It turns out that whena fault slips, straightforward calculations from the the pond, while surfa~:e waves are seen the mechanical process is equivalent to dimensions and amount of slip on the traveling away along the air/water a force operating on a lever arm of some fault and from the stiffness of the rocks interface. The sound-like waves in ¯ length, or a mechanical moment(the around the fault, it is possible for seismology are body waves, and the "units are torque, or Newtonstimes paleoseismologists to estimate the size concentric ripples moving away from meters). The seismic scalar momentof of earthquakes that may have occurred the source (the rock) at the surface are an earthquake is just the size of this on faults in the past. Furthermore, surface waves. The body wave torque, and is defined by seismologists can use the same technique to assess the size of an magnitude, is M0= ~Sp earthquake that mayoccur on a mb = logl0(A/T) + where ~ is the average amount of slip recognized fault in the future. To where the standard practice in the U.S. on the fault, S is the area of the fault, performthese calculations, it is is to measure the maximumamplitude, and/~ is a scale factor with units of force necessary to estimate the length and A, in microns, of the initial teleseismic per unit area, or pressure, called the width of the fault in question as well as P-wavearrival, T is its period (typically rigidity. The rigidity describes how the probable amount of slip and the less than 3 seconds), and Q is a term hard it is to bend the rocks in the rigidity of t~e rocks near the fault zone. that depends on distance and source earthquake source region with a A final measureof the size of an depth and minimizes the difference shearing motion. Both ~ and S can be earthquake is the total amount of between m~and other magnitude scales estimated from modern seismograms energy released in the slipping of the (there are always additive constants in and/or from ground rupture or fault. This is expressible in terms of the these formulas for this reason, and why aftershock patterns, while Ix is seismic~ momentas 0 it’s called m~instead of Mv no one estimated from laboratoryrock- E--M0(O/Ix) = 6S~ seems to know). The surface wave squeezing experiments.’ The scalar where ~ is the average shear stress (the momentdefines a magnitude scale ’magnitude is, similarly, force per unit area pushing the fault called the moment magnitude Ms = log10(A/T)+l.66 logA+3.3 along in units of pressure) along the M~s 2/3 loglo Me - 6.0. fault during the earthquake. Typically, where A is the maximumsurface wave ~is on the order of 100 times the amplitude and A is the source-to- Table 1 shows some surface-wave pressure of the atmosphere at the receiver distance in degrees (e.g., magnitudes and seismic moments for a few famous earthquakes.Note that the Earth’s surface, or in metric units, about quarter of the way around the Earth 10s Newtons per square meter. The would be D = 90°. Surface and body surface-wave magnitude (Ms) values aren’t all that different for the three very. energy released in a large earthquake is wave magnitudes may differ by up to gigantic. For the Chile earthquake it is several units, as shallower earthquakes large earthquakes in the table (Ms is release moreenergy near the Earth’S; actually smaller for the Chile event than E -, 10s x [800 x 10~] x [200 x 10s] x 21 surface and hence generate for the Alaska event) but the seismic = 3.4 x 1017 Joules proportionately larger surface waves moment and its corresponding moment For comparison, the energy released than deeper earthquakes. Surface wave magnitude show just how much larger mechanically the Alaska/rod Chile in a 1 megatonnuclear explosion is magnitude values for several "only" about 8 x 1013 Joules, so a very earthquakes are shownin Table 1. earthquakes were than the San large earthquake releases the energy Francisco event (the Chile event is just Note that all of these magnitude equivalent to about 10,000 hydrogen scales, although useful, are purely about as large an earthquake as the bombs! Fortunately for the humanrace, empirical and relative. They also Earth is thought to be capable of generating!). As the seismic moment most of this energy goes into fracturing contain an additional problem in that, and heating the rocks around the fault for technical reasons beyond the scope becomes more routinely estimated by and only a few percent actually gets of this article, they don’t do a very good earthquake monitoring agencies, you radiated away as seismic waves. job of discriminating between merely can expect to see the moment

Summer1994, Lite Geology NewMexico Bureau of Mines and Mineral Resources Who really knows where stones come from?

If you have ever applied yourself to back, whichis whyhe is paintingstones. your garden in early spring, to dig out, Greenone year, blue the next, white another. once and for all, every rock-only to S, omeday whena blue stone showsup he return the next season to find a new ,will havehis proof crop of rocks to pick out-you can This is for the samereasons sea shells are understand why people ponder this found halfway up MountEverest, the whole universal problem. The June 1991 issue load of plate tectonicsis drivenby stones of the Badger Comm~’Tater,the maga- crawlingtheir wayhome. If people had le~ zine of the Wisconsin Potato and stones plumbalone in the first place noneof Vegetable Grower’s Association~ this wouldhave happened.What with all featured an insightful article on this the coal dug out of the groundand shipped dilemma. Excerpts from the article, thousandsof miles away,the copperand "Where stones come from," by Justin iron ore andgold...the surfaceof the earthis Isherwood, are reprinted with permis- crawlingto beat heck. sion and appear in italics. Justin There is always a Scientist or two Isherwood is a potato grower from among any farm coven, and mytho- Plover, WI, and is a regul~ir columnist logical stone lbre sets them off. for the BadgerCommon "Tater. "...Stones don’t think, crawl, or get magnitude 7 earthquake squashed out of the ground .... Ever Farmers often ponder where stones feel the bottom of a rock? Colder than come from. It troubles some more than dirt, ain’t it? Cold in May when the others, usually for the reason those top of the rock is hot enoughto fry who are not troubled do not own stony sausages. Cold and wet. Sometimes land. after weeks of warmweather you find Farmers think about stones ice there. Tain~t the ice that does it because they have picked stones, picked though, it’s the dark side of that rock them last year and the year before. sucking water that does it. Frost heave Picked stones as far back as they can won’t get you any altitude even if you remember and their pa too. Every wait a thousand years. But the cold spring more stones, stones where none side of a rock sucking water day after existed before...In the farmships why day, season after season, brings rocks stones reappear every spring is up from thousands of feet down. We routinely discussed. Village folk argue ain’t never gonna be free of stones. If magnitude 8 earthquake other things, troublesome subjects like it was frost alone, we’d have won the national debt, greenhouse effect, and war a couple of generations ago. It acid rain. Transitory things like ain’t ice, it’s them stones sucking apartheid, black holes and stock prices. water just like a hydraulic cylinder But in the glacial valleys, in the lifts the stones out of the ground." dim rural taverns late at night they talk stones and why stones come back We encourage our readers to to the fields year after year like migrat- write to us with scientific, or ing geese. humorous explanations about One farmer confesses he has taken where stones-especially the to painting the rocks he picks because reappearing kind-come from, or to he swears they look like the ones he share other stories of folk geology. picked several years previous... He Sotu’ce believes stones comeback, howhe throws Isherwood,J., (1991) Wherestones come magnitude 9 earthquake "emon a rock pile and they zoon’t’stayput, from, in Houlihan,T. (ed), Badger instead crawlofflike woundeddogs to lick Common’Tater: WisconsinPotato and their woundsand return to the field...Stones VegetableGrower’s Association, Antigo, have a hominginstinct. Dump"era in Wisconsin,v. 43, no. 6, pp. 38-39. Romania,he says, and they’ll find their way

New Mexico Bureau of Mines and Minerai Resources Lite Geology, Summer1994 \ AncientLakes: A Tool For Understandirlg Climatic Change

Bruce Allen wind into the old lake sediments. features such as beach ridges, spits, and Departmentof Earth and Planetery Sciences, Highway 60 passes through the sand bars that formed along the University of NewMexico exposed remains of ancient Lake margins of pluvial lakes. Other more Oneof the attractions of living in Estancia (Fig. 2). The blowoufs now complete information about the rise the southwestern United States is its contain small, ephemeral salt ponds, or and fall of lake level is obtained by dry air and clear, blue skies that seem playas" Salt from these playas was studying the sediments that were to linger for weeks on end. Although harvested by the people of the Salinas deposited on the bottoms of the lakes. thunderstorms being sporadic rains Pueblos at Quarai and Gran Quivers. At Estancia, for example, whenthe lake during summer months, and cyclones Evidence for the expansion and was freshened and expanded in size, bearing moisture from contraction of ancient lakes provides aquatic wormsand other bottom- the Pacific Ocean sweep dwelling organisms through the region colonized the lake during winter months, bottom and mixed the the overall climate of the Estancla uppermost layer of the Southwestis dry, ra fact bottom muds in their that is borne ’out by the I search for food. scarcity of large, natural Sediments that were lakes in the region. deposited during Geological evidence highstands of the lake indicates that such was are relatively not always the case. If homogenous due to this mixing (called we could travel back in 1-40 ) time about 20,000 years, bioturbation). During during the height of the HighestShoreline of lowstands of the lake, last Ice Age, we would Ancient Lake Estanola as salinity increased, find that manyof the 2’//~ bioturbating .organisms ,2 intermontane basins in were eliminated from the Southwest were the lake bottom, occupied by large lakes. resulting in delicately These ancient lakes are laminated sediments. called pluvial lakes Still another because they formed indicator of highstands when the climate was and lowstands is the wetter than it is today. abundant remains of tiny crustaceans called New Mexico had - Modern several large, pluvial eo ostracodes ("seed ~.. Salt Ponds shrimp"). Ostracodes lakes. One such lake .T , (Playas) are used to estimate filled the bottomof the % Estancia Valley, east of changesi n the salinity the Manzano Mountains of the lake in which in central NewMexico. I they lived. Biologists The northern shore 20 miles studying modern reached the outskirts of ostracodes have what is now M0riarty, determined that certain NM(Fig. 1). At its Figure 1. Mapsho~ving location of the Estancia basin and extent species of ostracodes can tolerate and even maximumextent, Lake of former lake as indicated by stranded shorelines. ’ Estancia was about 40 thrive in water thaf has miles long and 20 miles high salinity. Other wide and covered the town sites of scientists with a powerful tool for species are able to tolerate only fresh Estancia and Willard with almost 100, understanding how the Earth’s~climate water. Changes in the abundance and feet of water (Fig. 1). Today,a few . has changedover the past several tens types of ostracodes in the deposits of , miles east of Willard, NM,huge cup- of thousands of years. Past fluctuations Lake Estancia can be used to determine shaped depressions, or blowouts, some in lake level can be documentedby when the ancient/ake was freshened a mile in diameter, have been carved by mapping the elevation of shoreline and expanded in size, and when the

Summer1994, Lite Geology New Mexico Bureau of Mines at~d Mineral Resources basin floor, and the bottoms of the blowouts are beginning to fill in with sediment. Someof the earliest attempts to estimate past climates were done in the mid-1900’s by using the Estancia Valley and its shorelines to construct a hydrologic-balance model. In its simplest form, the hydrologic-balance model keeps track of the volume of ’water that enters and leaves the lake. Lake Estancia, as for manyof the pluvial lakes in the Southwest, did not overflow and the removal of water from the lake was largely through evaporation from the lake surface. Inputs of water into the lake included direct precipitation on the lake surface, Figure 2--Wind deflation of the central basin began ~8,000 years ago, runoff from the surrounding drainage resulting in the formation of numerousblowouts that presently contain basin, and ground-water discharge. ephemeral salt pp’nds, or playas. These early studies suggested that highstands were the result of both lower temperatures (lower evaporation water became salty during Iowstands The effects of dramatic changes in rates) and increased precipitation. of the lake. climate continued to be imposed on the A topic that is of great interest and The climatic history of Lake floor of the Estancia Valley, and on importance today is how quickly large Estancia, as recorded by its sediments, other desiccated pluvial lake basins in changes in climate, such as those can be read in the walls of the many the Southwest, long after the lakes recorded by Lake Estancia, mayoccur. blowouts that excavated the floor of the dried up. The large blowouts cut into’ The first good evidence that the Earth’s old ~ake. The upper 15 feet of the lake sediments at Estancia (Fig. 2), climate has undergone large and sediments exposed in the blowouts for example, began to be excavated abrupt changes in climate has come contains two thick beds of nearly pure roughly 8,000 years ago clay that are bioturbated, indicating as southwesterly winds highstands of the lake. Radiocarbon blew across the dating of the older of the two clay beds abandc)ned lake bottom. tells us that the first highstand began Dried pellets of clay suddenly about 20,000 years ago, and gypsum, scooped forming the highest set of shorelines out by the wind, were that nowlie stranded along the margins deposited nearby as of the Estancia Valley (Fig. 1). Then, just giant dunes called as suddenly, about 15,000 years ago, the lunettes, in reference to climate changed dramatically and the the crescent shape of the lake dropped to a low elevation (Fig.4), dunes. This process of ¯"~.- .,~,-._..,,..~..... ". "r ",, ¯ salinity increased, bioturbation "deflation" continued stopped, and only the most saline- until the blowouts ¯.--’oA.:: ,, ,. .~,"~"=,q’ .....,. ¯" "’,,, ."I". tolerant slbecies of ostracodes survived reached a depth of ¯ in the lake water. This contraction of the about 30 feet below the lake lasted for about 1000 years and was floor of the basin. An followed by another rapid expansion overall rise in the water beginning about 14,000 years ago (Fig. table during the past 4). This last major expansion of the few thousand years duE’ lake, however, was not as extensive or to relatively wetter Figure 3--Photograph of a blowout (large depression long-lived as the earlier highstand, and climatic conditions has excavated by the wind) in the Estancia basin. Layered by 12,000 years ago the lake began its reversed the trend sediments in the wall of the blowout were deposited final disappearance from the landscape. towards deflation of the in ancient Lake Estancia during the last Ice Age. New Mexico Bureau of Mines and Mineral Resources Lite Geology, Summer1994 ~J EstanclaValley, NM, Lake-Leveland The accumulating evidence for large 6200 Water-TableFluctuations and abrupt changes in climate and for a metastable climatic system is causing Elevationof BasinFloor climatologists to reconsider scenarios for global climate change. Prospects for "global warming" from the Deflation introduction of carbon dioxide into the atmosphere have been highly , ~ 6100 Infllllng publicized, but the prediction of the magnitude and time-scale ior such a ,/ human-caused event is hampered by an incomplete understanding of, natural ! climatic variability. Records of " 6000 ¯ paleoclimate from different parts of the 20 16 12 8 4 0 world that resolve climatic changes on ThousandsOf YearsAgo a time scale of decades, such as the one being reconstructed for Lake Estancia, will be needed in order to understand Figure 4--Flu(~tuations in lake level and water table in the Estancia basin howthe earth’s climatic system occurred during the last 20,000 years. Notice a rapid rise in lake level operates and to predict future changes -20,000 years ago and a rapid fall ~15,000 years ago, followed by several . due to both natural variability and other high lake stands. humanactivity. SuggestedReading from cores collected from the freshened the lake, just as suddenly, Allen,B.D., and Anderson, R.Y.i 1993, Greenland Ice Cap. Ice cores extend ostracodes that live in fresh water ~ Evider)cefrom western North from the present back through the last reproduced in great numbers. The -’ Americafor rapid shifts in climate Ice Ageand indicate that dramatic shifts lake/during that single climatic duringthe last glacial maximum: in temperature and other climatic episode -20,000 years ago, rose to its Science,v. 260,pp. 1920-1923. , I variables, at that high latitude, occurred high shoreline within a few decades Bradley,R.S., 1985,Quaternary within a few years to a few decades. and during the next 5,000 yeats it was Paleoclimatology:Boston, Unwin The abrupt shifts in climate suggest sustained near its highest elevation by Hyman,472 pp. that the earth’s climatic system is other brief episodes of increased Smith,G.I., andStneet-Perrott, EA., capable of "flipping" b~ack and forth precipitation (Fig. 4). 1983,Pluvial lakes of the western betweenrelatively stable states in very Although most of the moisture that Unit~.

Summer.1994, Life Geology New Mexico Bureau of Mines and Mineral Resources .e ¯ ,h 1. g h L I T E S EARTH SCIENCE UPDATE

Upcoming Events November18 and 19,1994 TeacherResources: The Fall Conferenceof the NewMexico Howto Teach with Topographic Maps,’ November3-5,1994 Science Teachers Association and New for grades 5 through 10, is a 24-page NewMexico Science OlympiadFall Mexico Math Teachers Association booklet containing student activities, Workshopfor teachers will be held on will be held in Albuquerque at the and includes a topographic map by the the campus of New Mexico Tech in Hilton Hotel. For more U.S. Geological Survey. Teachers and Socorro. For MoreInformation call information, contact Cindy Lauster, students can learn to read topographic Vannetta Perr~ (505) 835-5678. 11520 Pase6 del Oso NE, maps, and even construct a topo map of Albuqueruqe, NM 87111. their ownschool yard. Contact: National Science TeachersAssociation, Publication Sales;1840 Wilson Blyd., Lite Geology evolves: Arlington, VA22201; phone (800) 722- Lite Geologybegan as a small Earth-science publication designed and scaled for 6782 or (703) 243-7100. The price NewMexico. Our subscription list has grown tremendously during the past two $7.95 plus $3.75 shipping. years, and nowincludes a large numberof out-of-state readers. In order to keep up with the demandfor this publication from outside of NewMexico, we will charge Su’rface of the Earth coior~relief map $4.00 per year for out-of-state readers, which covers the cost of printing and poster measures31 x 43" and is a mailing Lite Geology. The subscription year begins with the Fall issue, and ends computer-generated color image of the with the Summerissue to correspond with the acaderdic year. This current issue, topography of the world. The price is Summer1994, is thelast of the free issues that you will receive if you reside $20.00 which includes shipping (for outside of NewMexico. Wethank all of our readers for their enthusiastic support, U.S.A. orders). To order, request Report and hope that all of you will continue to subscribe. If ybu have questions about MGG--5from National Geophysical your subscription, please cal! Theresa Lopez at (505) 835-5420. Thanks! ---ed. Data Center, NOAAE/GC4, 325 Broadway, Boulder, CO 80303--3328; phone (303) 497--6338. Lite Geology Creative Dimensions 1994 Catalogof Science kits, materials and books lists *Please send me Lite Geology D **($4.00 enclosed for out-of-state subscribers] an abundance of fo~il and mineral activity and investigative kits. For a NamP free copyof this catalog, write to: Mailing address Creative Dimensions, P.O. Box 1393, Bellingham, Washington, 98227. City State Zip

Science Fare 1994 Catalogoffers a range Howdid you hear about Lite Geology? of science supplies, including rock Are you a teacher? specimens and mineral study kits. For a free catalog, write to: ScienceFare, 8246 At what school dO you teach? Menaul Blvd NE, Albuquerque, NM Grade level? 87110. Subject(s)

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New Mexico Bureau of Mines and Mineral Resources Lite Geology, Summer1994 L I T E

" ~k I t 4 geologlststudies hot sprlngs... As a follow-up to our last issue, we have continued to explore is published quarterly by NewMexico earthquakes. We hope that our readers will be more able to interpret Bureau of Mines and Mineral Resources news about earthquakes-why they occur, how they are measured,;and (Dr. Charles E. Chapin,Director and State how they influence local geology, such as in the geyser fields of Geologist), a division of NewMexico Tech Yellowstone. Although New Mexico does not have geysers to explore, (Dr. Daniel H. Lope~,President). there are a few geothermal areas in the state that have hot springs. The Purpose: to help build earth science NMBM&MRhas about a dozen publications that discuss New Mexico’s awareness by presenting ed’ucato~ and geothermal resources. These Bulletins, Circulars, and Hydrologic Reports the public with contemporarygeologic are listed in the current price list available through the NMBM&MR topics, issues, and events. UseLite Geology Publications Office, (505) 835-5410. See you next issuel as a source for ideas in the classroomor for public education. Reploductionis Lite Geology Staff encouraged with proper recognition of the source. All rights reservedon copyrightedmaterial reprinted with permissionwithin this issue. Lite GeologyStaff Information Editor: SusanJ. Welch GeologicalEditors: Dr. DaveLove and Dr. Charles Chapin Educational Coordinator:Barbara Popp Graphic Designer: Jan Thomas Cartoonist: Jan Thomaswithinspiration from Dr. Peter Mozley Editorial Assistants: TobyClick and Lois Gollmer Creativeand TechnicalSupport: - NMBM&MRStaff ~lailing Add~ss NewMexico Bureau of Mines and Mineral hot sp, rings Resources, Socorro, NM87801. Phone (505) 835-5420.For a subscription information,please call or write. Life Geologyis printed on recycled paper.

L I T E ~o, lsras~ g, gy U.S.P(~TAGE New Mexico Bureau of Mines PAID and Mineral Resources Publications Office Socorro, NM87801

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Summer1994, Lite Geology New Mexico Bureau of Mines and Mineral Resources