From Moonscape to Landscape
[Illustration: {uncaptioned}]
[Illustration: _What last happened here about 2,000 years ago looked
much like this photograph of a volcanic eruption in Hawaii.
Bubbling, pooling, and flowing lava blanketed the landscape as
molten materials poured or gushed out of the Earth. Most volcanic
phenomena preserved at Craters of the Moon have been seen in action
in Hawaii._]
Geology of the Craters of the Moon
A 400-mile-long arc known as the Snake River Plain cuts a swath from 30
to 125 miles wide across southern Idaho. Idaho’s official state highway
map, which depicts mountains with shades of green, shows this arc as
white because there is comparatively little variation here compared to
most of the state. Upon this plain, immense amounts of lava from within
the Earth have been deposited by volcanic activity dating back more than
14 million years. However, some of these lavas, notably those at Craters
of the Moon National Monument, emerged from the Earth as recently as
2,000 years ago. Craters of the Moon contains some of the best examples
of basaltic volcanism in the world. To understand what happened here,
you must understand the Snake River Plain.
Basaltic and Rhyolitic Lavas. The lavas deposited on the Snake River
Plain were mainly of two types classified as basaltic and rhyolitic.
Magma, the molten rock material beneath the surface of the Earth, issues
from a volcano as lava. The composition of this fluid rock material
varies. Basaltic lavas are composed of magma originating at the boundary
of the Earth’s mantle and its crustal layer. Rhyolitic lavas originate
from crustal material. To explain its past, geologists now divide the
Snake River Plain into eastern and western units. The following geologic
story relates to the eastern Snake River Plain, on which Craters of the
Moon lies.
On the eastern Snake River Plain, basaltic and rhyolitic lavas formed in
two different stages of volcanic activity. Younger basaltic lavas mostly
lie atop older rhyolitic lavas. This portion of the plain runs from
north of Twin Falls eastward to the Yellowstone area on the
Wyoming-Montana border. Drilling to depths of almost 2 miles near the
plain’s midline, geologists found ½ mile of basaltic lava flows lying
atop more than 1½ miles of rhyolitic lava flows. How much deeper the
rhyolitic lavas may extend is not known. No one has drilled deeper here.
[Illustration: _Crossing Idaho in an arc, the Snake River Plain
marks the path of the Earth’s crustal plate as it migrates over a
heat source unusually close to the surface. It is believed that the
heat source fueling Yellowstone’s thermal features today is
essentially the same one that produced volcanic episodes at Craters
of the Moon ending about 2,000 years ago._]
This combination—a thinner layer of younger basaltic lavas lying atop an
older and thicker layer of rhyolitic lavas—is typical of volcanic
activity associated with an unusual heat phenomenon inside the Earth
that some geologists have described as a mantle plume. The mantle plume
theory was developed in the early 1970s as an explanation for the
creation of the Hawaiian Islands. According to the theory, uneven
heating within the Earth’s core allows some material in the overlying
mantle to become slightly hotter than surrounding material. As its
temperature increases, its density decreases. Thus it becomes relatively
buoyant and rises through the cooler materials—like a tennis ball
released underwater—toward the Earth’s crust. When this molten material
reaches the crust it eventually melts and pushes itself through the
crust and it erupts onto the Earth’s surface as molten lava.
The Earth’s crust is made up of numerous plates that float upon an
underlying mantle layer. Therefore, over time, the presence of an
unusual heat source created by a mantle plume will be expressed at the
Earth’s surface—floating in a constant direction above it—as a line of
volcanic eruptions. The Snake River Plain records the progress of the
North American crustal plate—350 miles in 15 million years—over a heat
source now located below Yellowstone. The Hawaiian chain of islands
marks a similar line. Because the mechanisms that cause this geologic
action are not well understood, many geologists refer to this simply as
a heat source rather than a mantle plume.
Two Stages of Volcanism. As described above, volcanic eruptions
associated with this heat source occur in two stages, rhyolitic and
basaltic. As the upwelling magma from the mantle collects in a chamber
as it enters the Earth’s lower crust, its heat begins to melt the
surrounding crustal rock. Since this rock contains a large amount of
silica, it forms a thick and pasty rhyolitic magma. Rhyolitic magma is
lighter than the overlying crustal rocks, therefore, it begins to rise
and form a second magma chamber very close to the Earth’s surface. As
more and more of this gas-charged rhyolitic magma collects in this upper
crustal chamber, the gas pressure builds to a point at which the magma
explodes through the Earth’s crust.
Explosive Rhyolitic Volcanism. Rhyolitic explosions tend to be
devastating. When the gas-charged molten material reaches the surface of
the Earth, the gas expands rapidly, perhaps as much as 25 to 75 times by
volume. The reaction is similar to the bubbles that form in a bottle of
soda pop that has been shaken. You can shake the container and the
pressure-bottled liquid will retain its volume as long as the cap is
tightly sealed. Release the pressure by removing the bottle cap,
however, and the soft drink will spray all over the room and occupy a
volume of space far larger than the bottle from which it issued. This
initial vast spray is then followed by a foaming action as the less
gas-charged liquid now bubbles out of the bottle.
Collectively, the numerous rhyolitic explosions that occurred on the
Snake River Plain ejected hundreds of cubic miles of material into the
atmosphere and onto the Earth’s surface. In contrast, the eruption of
Mount Saint Helens in 1980, which killed 65 people and devastated 150
square miles of forest, produced less than 1 cubic mile of ejected
material. So much material was ejected in the massive rhyolitic
explosions in the Snake River Plain that the Earth’s surface collapsed
to form huge depressions known as calderas. (Like _caldron_, whose root
meaning it shares, this name implies both bowl-shaped and warmed.) Most
evidence of these gigantic explosive volcanoes in the Snake River Plain
has been covered by subsequent flows of basaltic lava. However, traces
of rhyolitic eruptions are found along the margins of the plain and in
the Yellowstone area.
Quiet Outpourings of Basaltic Lava. As this area of the Earth’s crust
passed over and then beyond the sub-surface heat source, the explosive
volcanism of the rhyolitic stage ceased. The heat contained in the
Earth’s upper mantle and crust, however, remained and continued to
produce upwelling magma. This was basaltic magma that, because it
contained less silica than rhyolite, was very fluid.
The basalt, like the rhyolite, collected in isolated magma chambers
within the crust until pressures built up to force it to the surface
through various cracks and fissures. These weak spots in the Earth’s
crust were the results of earlier geologic activity, expansion of the
magma chamber, or the formation of a rift zone.
[Illustration: _Microscopic cross section of basaltic rock._]
[Illustration: _Microscopic cross section of rhyolitic rock. Cross
sections show vastly different textures. Rhyolitic magma contains
more silica; it is very thick and does not allow trapped gas to
escape easily. Its volcanic eruptions blast large craters in the
Earth’s crust. Basaltic magma is more fluid and allows gas to escape
readily. It erupts more gently. Here in the eastern Snake River
Plain, basaltic lava flows almost completely cover earlier rhyolitic
deposits._]
(_continued on page 28_)
Identifying the Lava Flows
At Craters of the Moon the black rocks are lava flows. The surface
lava rocks, basaltic in composition, formed from magma originating
deep in the Earth. They are named for their appearances: Pahoehoe
(pronounced “pah-hoy-hoy” and meaning “ropey”), Aa (pronounced “ah-ah”
and meaning “rough”), or Blocky. Geologists have seen how these flows
behave in modern volcanic episodes in Hawaii and elsewhere.
[Illustration: _Pahoehoe lava_]
Pahoehoe More than half the park is covered by pahoehoe lava flows.
Rivers of molten rock, they harden quickly to a relatively smooth
surface, billowly, hummocky, or flat. Other pahoehoe formations
resemble coiled, heavy rope or ice jams.
[Illustration: _Aa lava_]
Aa Aa flows are far more rugged than pahoehoe flows. Most occur when a
pahoehoe flow cools, thickens, and then turns into aa. Often
impassable to those traveling afoot, aa flows quickly chew up hiking
boots. Blocky lava is a variety of aa lava whose relatively large
silica content makes it thick and often dense, glassy, and smooth.
[Illustration: _Blocky lava_]
Bombs Lava pieces blown out of craters may solidify in flight. They
are classed by shape: spindle, ribbon, and breadcrust. Bombs range
from ½ inch to more than 3 feet long.
Tree Molds When molten lava advances on a living forest, resulting
tree molds may record impressions of charred surfaces of trees in the
lava.
[Illustration: _Blue Dragon Flows lava_]
[Illustration: _Breadcrust bomb_]
[Illustration: _Spindle bomb_]
[Illustration: _Wood-like lava_]
[Illustration: _Tree mold_]
[Illustration: _Lava river_]
[Illustration: _Mt. St. Helens erupts in 1980. Because the lava
contained a large amount of silica, its explosive eruption contrasts
sharply with recent basaltic flows in volcanic activity in Hawaii._]
[Illustration: Basaltic flows in Hawaii.]
Upon reaching the surface, the gases contained within the lava easily
escaped and produced rather mild eruptions. Instead of exploding into
the air like earlier rhyolitic activity, the more fluid basaltic lava
flooded out onto the surrounding landscape. These flows were fairly
extensive and often covered many square miles. After millions of years,
most of the older rhyolitic deposits have been covered by these basaltic
lava flows.
The Great Rift and Craters of the Moon. Craters of the Moon National
Monument lies along a volcanic rift zone. Rift zones occur where the
Earth’s crust is being pulled in opposite directions. Geologists believe
that the interactions of the Earth’s crustal plates in the vicinity of
the Snake River Plain have stretched, thinned, and weakened the Earth’s
crust so that cracks have formed both on and below the surface here.
Magma under pressure can follow these cracks and fissures to the
surface. While there are many volcanic rift zones throughout the Snake
River Plain, the most extensive is the Great Rift that runs through
Craters of the Moon. The Great Rift is approximately 60 miles long and
it ranges in width from 1½ to 5 miles. It is marked by short cracks—less
than 1 mile in length—and the alignment of more than 25 volcanic cinder
cones. It is the site of origin for more than 60 different lava flows
that make up the Craters of the Moon Lava Field.
Eight Major Eruptive Periods. Most of the lavas exposed at Craters of
the Moon formed between 2,000 and 15,000 years ago in basaltic eruptions
that comprise the second stage of volcanism associated with the mantle
plume theory. These eight eruptive periods each lasted about 1,000 years
or less and were separated by periods of relative calm that lasted for a
few hundred to more than 2,000 years. These sequences of eruptions and
calm periods are caused by the alternating build up and release of
magmatic pressure inside the Earth. Once an eruption releases this
pressure, time is required for it to build up again.
Eruptions have been dated by two methods: paleomagnetic and radiocarbon
dating. Paleomagnetic dating compares the alignment of magnetic minerals
within the rock of flows with past orientations of the Earth’s magnetic
fields. Radiocarbon dating makes use of radioactive carbon-14 in
charcoal created from vegetation that is overrun by lava flows. Dates
obtained by both methods are considered to be accurate to within about
100 years.
A Typical Eruption at Craters of the Moon. Research at the monument and
observations of similar eruptions in Hawaii and Iceland suggest the
following scenario for a typical eruption at Craters of the Moon.
Various forces combine to cause a section of the Great Rift to pull
apart. When the forces that tend to pull the Earth’s crust apart are
combined with the forces created as magma accumulates, the crust becomes
weakened and cracks form. As the magma rises buoyantly within these
cracks, the pressure exerted on it is reduced and the gases within the
magma begin to expand. As gas continues to expand, the magma becomes
frothy.
At first the lava is very fluid and charged with gas. Eruptions begin as
a long line of fountains that reach heights of 1,000 feet or less and
are up to a mile in length. This “curtain of fire eruption” mainly
produces cinders and frothy, fluid lava. After hours or days, the
expansion of gases decreases and eruptions become less violent. Segments
of the fissure seal off and eruptions become smaller and more localized.
Cinders thrown up in the air now build piles around individual vents and
form cinder cones.
With further reductions in the gas content of the magma, the volcanic
activity again changes. Huge outpourings of lava are pumped out of the
various fissures or the vents of cinder cones and form lava flows. Lava
flows may form over periods of months or possibly a few years. Long-term
eruptions of lava flows from a single vent become the source of most of
the material produced during a sustained eruption. As gas pressure falls
and magma is depleted, flows subside. Finally, all activity stops.
When Will the Next Eruption Occur? Craters of the Moon is not an extinct
volcanic area. It is merely in a dormant stage of its eruptive sequence.
By dating the lava flow, geologists have shown that the volcanic
activity along the Great Rift has been persistent over the last 15,000
years, occurring approximately every 2,000 years. Because the last
eruptions took place about 2,000 years ago, geologists believe that
eruptions are due here again—probably within the next 1,000 years.
[Illustration: _From the air the Great Rift looks like an
irregularly dashed line punctuated by tell-tale cones and craters._]
[Illustration: _Chainlike, the Hawaiian group of islands traces the
migration of Earth’s crustal plate over an unusual undersea heat
source. The Hawaiian chain of islands and the Snake River Plain map
similar happenings._]
(_continued on page 34_)
Indian Tunnel
[Illustration: {uncaptioned}]
Indian Tunnel looks like a cave, but it is a lava tube. When a
pahoehoe lava flow is exposed to the air, its surface begins to cool
and harden. A crust or skin develops. As the flow moves away from its
source, the crust thickens and forms an insulating barrier between
cool air and molten material in the flow’s interior. A rigid roof now
exists over the stream of lava whose molten core moves forward at a
steady pace. As the flow of lava from the source vent is depleted, the
level of lava within the molten core gradually begins to drop. The
flowing interior then pulls away from the hardening roof above and
slowly drains away and out. The roof and last remnants of the lava
river inside it cool and harden, leaving a tube.
[Illustration: _Lava tube_]
[Illustration: _Great horned owl_]
Many lava tubes make up the Indian Tunnel Lava Tube System. These
tubes formed during the same eruption within a single lava flow whose
source was a fissure or crack in the Big Craters/Spatter Cones area. A
tremendous amount of lava was pumped out here, forming the Blue Dragon
Flows. (Hundreds of tiny crystals on its surface produce the color
blue when light strikes them.) Lava forced through the roof of the
tube system formed huge ponds whose surfaces cooled and began to
harden. Later these ponds collapsed as lava drained back into the lava
tubes. Big Sink is the largest of these collapses. Blue Dragon Flows
cover an area of more than 100 square miles. Hidden beneath are miles
of lava tubes, but collapsed roof sections called skylights provide
entry to only a small part of the system. Only time, with the collapse
of more roofs, will reveal the total extent of the system.
[Illustration: _Icicles (ice stalactites)_]
[Illustration: _Lava stalactites_]
Stalactites Dripped from hot ceilings, lava forms stalactites that
hang from above. Mineral deposits Sulfate compounds formed on many
lava tube ceilings from volcanic gases or by evaporation of matter
leached from rocks above. Ice In spring, ice stalactites form on cave
ceilings and walls. Ice stalagmites form on the cave floor. Summer
heat destroys these features. Wildlife Lava tube beetles, bushy-tailed
woodrats (packrats), and bats live in some dark caves. Violet-green
swallows, great horned owls, and ravens may use wall cracks and
shelves of well-lit caves for nesting sites.
Cinder Cones and Spatter Cones
[Illustration: {uncaptioned}]
[Illustration: _Cinder cone_]
[Illustration: _Spatter cone_]
Cinder Cones When volcanic eruptions of fairly moderate strength throw
cinders into the air, cinder cones may be built up. These cone-shaped
hills are usually truncated, looking as though their tops were sliced
off. Usually, a bowl- or funnel-shaped crater will form inside the
cone. Cinders, which cooled rapidly while falling through the air, are
highly porous with gas vesicles, like bubbles. Cinder cones hundreds
of feet high may be built in a few days. Big Cinder Butte is a cinder
cone. At 700 feet high it is the tallest cone in the park. The shape
develops because the largest fragments, and in fact most of the
fragments, fall closest to the vent. The angle of slope is usually
about 30 degrees. Some cinder cones, such as North Crater, the
Watchman, and Sheep Trail Butte, were built by more than one eruptive
episode. Younger lava was added to them as a vent was rejuvenated. If
strong winds prevailed during a cinder cone’s formation, the cone may
be elongated—in the direction the wind was blowing—rather than
circular. Grassy, Paisley, Sunset, and Inferno Cones are elongated to
the east because the dominant winds in this area come from the west.
The northernmost section of the Great Rift contains the most cinder
cones for three reasons: 1. There were more eruptions at that end of
the rift. 2. The lavas erupted there were thicker, resulting in more
explosive eruptions. (They are more viscous because they contain more
silica.) 3. Large amounts of groundwater may have been present at the
northern boundary of the lavas and when it came in contact with magma
it generated huge amounts of steam. All of these conditions lead to
more extensive and more explosive eruptions that tend to create cinder
cones rather than lava flows.
Spatter Cones When most of its gas content has dissipated, lava
becomes less frothy and more tacky. Then it is tossed out of the vent
as globs or clots of lava paste called spatter. The clots partially
weld together to build up spatter cones. Spatter cones are typically
much smaller than cinder cones, but they may have steeper sides. The
Spatter Cones area of the park (Stop 5 on the map of the Loop Drive)
contains one of the most perfect spatter-cone chains in the world.
These cones are all less than 50 feet high and less than 100 feet in
diameter.
[Illustration: _Lichens often pioneer new life on Earth. Two plants
in one, lichens are composed of an alga and a fungus growing
together to their mutual benefit, usually on rock. Hardy and
slow-growing, lichens help break down rock to soil-building mineral
matter._
_Eventually their vegetable matter decays, helping to form the first
soils that other plants can then use. Tough in the extreme, some
lichens can be heated to high temperatures and still be capable of
resuming normal growth when returned to viable conditions._]
Life Adapts to a Volcanic Landscape
Two thousand years after volcanic eruptions subsided, plants and animals
still struggle to gain toeholds on this unforgiving lava field. Much of
the world’s vegetation could not survive here at all. Environmental
stresses created by scant soil and minimal moisture are compounded by
highly porous cinders that are incapable of holding water near the
ground surface where plants and other organisms can make ready use of
it. Scarce at best—total average precipitation is between 15 to 20
inches per year—rainwater and snowmelt quickly slip down out of reach of
the plants growing on cinder cones. Summer’s hot, dry winds rob moisture
from all living things exposed to them. Whisking across leaves and
needles the winds carry away moisture precious to plant tissues. On the
side of a cinder cone, summer day temperatures at ground level can be
more than 150°F.
The secret to survival here is adaptation. Most life forms cope by
strategies of either resisting or evading the extremes of this semi-arid
climate. To resist being robbed of moisture by winds and heat, a plant
may feature very small leaves that minimize moisture loss. To evade
heat, wind, and aridity, another plant may grow inside a crevice that
provides life-giving shade and collects precious moisture and soil
particles. Another plant may spend about 95 percent of the year dormant.
It may rush through the germination, sprouting, leafing out, blooming,
and fruiting stages and return to the dormancy of its seed stage in just
two weeks. The dwarf buckwheat has adapted to life on porous cinders by
evolving a root system that may spread out for up to 3 feet to support
its aboveground part, which is a mere 4 inches high. This buckwheat only
looks like a dwarf because you can not see its roots.
(_continued on page 40_)
Plants Adapt to a Volcanic Landscape
[Illustration: {uncaptioned}]
Water is the limiting factor in plant growth and reproduction both on
the lava fields of Craters of the Moon and on the surrounding
sagebrush steppe. Plants have developed a combination of adaptations
to cope with drought conditions. There are three major strategies:
1. Drought tolerance Physiological adaptations leading to drought
tolerance are typical of desert plant species. The tissues of some
plants can withstand extreme dehydration without suffering permanent
cell damage. Some plants can extract water from very dry soils.
Sagebrush and antelope bitterbrush exemplify drought tolerance.
[Illustration: _Dwarf monkeyflower_]
[Illustration: _Buckwheat_]
2. Drought avoidance Certain structural modifications can enable
plants to retain or conserve water. Common adaptations of this type
include small leaves, hairiness, and succulence. The small leaves of
the antelope bitterbrush expose less area to evaporative influences
such as heat and wind. Hairs on the scorpionweed reduce surface
evaporation by inhibiting air flow and reflecting sunlight. Succulent
plants such as pricklypear cactus have tissues that can store water
for use during drought periods. Other plants, such as wire lettuce,
avoid drought by having very little leaf surface compared to their
overall volume.
3. Drought escape Some plants, such as mosses and ferns, escape
drought by growing near persistent water supplies such as natural
potholes and seeps from ice caves. Many other drought escapers, such
as dwarf monkeyflower, simply carry out their full life cycle during
the moist time of the year. The rest of the year they survive in seed
form.
[Illustration: _Pricklypear cactus_]
[Illustration: _Ferns_]
Plant Microhabitats
[Illustration: {uncaptioned}]
Lava flows Most plants cannot grow on lava flows until enough soil has
accumulated to support them. The park’s older volcanic landscapes,
where soils are best developed, are clothed with sagebrush-grassland
vegetation. On younger lava flows, bits of soil first accumulate in
cracks, joints, and crevices. It is in these microhabitats that
vascular plants may gain footholds. Narrow cracks and joints may
contain desert parsley and lava phlox. Shallow crevices will hold
scabland penstemon, fernleaf fleabane, and gland cinquefoil. Deep
crevices can support the syringa, various ferns, bush rockspirea,
tansybush, and even limber pine. Not until full soil cover is achieved
can the antelope bitterbrush, rubber rabbitbrush, and sagebrush find
suitable niches. On lava flows soils first form from eroded lava and
the slow decomposition of lichens and other plants able to colonize
bare rock. These soils can be supplemented by wind-blown soil
particles until vascular plants gain footholds. As plants begin to
grow and then die, their gradual decomposition adds further soil
matter. These soil beginnings accumulate in cracks and crevices, which
also provide critical shade and wind protection. Deep crevices provide
lower temperatures favoring plant survival.
[Illustration: _Rubber rabbitbrush_]
[Illustration: _Syringa_]
Cinder gardens Compared to the lava flows, cinder cones are much more
quickly invaded by plants. Here, too, however, volcanic origins
influence plant growth. Compared to the relatively level lava flows,
steeply sloping cinder cones introduce a new factor that controls the
development of plant communities: topography. Here you find marked
differences in the plant communities between the north- and
south-facing slopes. South-facing slopes are exposed to prolonged,
intense sunlight, resulting in high evaporation of water. Because of
the prevailing winds, snow accumulates on northeast sides of cones,
giving them far more annual water than southwest-facing sides receive.
The pioneering herbs that first colonize cinder cones will persist on
southwest-facing slopes long after succeeding plant communities have
come to dominate north-facing slopes. It is on these north-facing
slopes that limber pine first develops in the cinder garden.
South-facing slopes may never support the limber pine but may be
dominated by shrubs. Unweathered cinder particles range in size from 3
to 4 inches in diameter down to very small particles. They average
about ¼ inch in diameter.
[Illustration: _Cinquefoil_]
[Illustration: _Wire lettuce_]
Ecological conditions at Craters of the Moon are generally so harsh that
slight changes can make the difference for the survival of a plant or
other organism. Life thrives in many rock crevices that are surrounded
by barren exposed lava rock of the same physical composition. These
microhabitats provide the critical shade and increased soil and moisture
content required for plant survival. Over the years, particles of soil
will naturally collect in rock crevices, which also have the effect of
funneling precipitation into their depths. Their shade further protects
these pockets of soil and water from wind erosion, excessive heat, and
evaporation and leaching by direct sunlight.
[Illustration: _Limber pines are the tree pioneers of the lava
terrain. Their seedlings often find suitable conditions for
germination in rock crevices long before surrounding landscapes
support tree growth. Most common of all the park’s trees, limber
pine is named for its flexible branches. Many park animals depend on
this tree in some fashion for their livelihoods._]
[Illustration: _Limber pine cones stay green and resinous through
their first year of development and then turn brown and woody as
their seeds mature in the second year. Cones grow to about 4 inches
long._]
At Craters of the Moon, crevices are of such importance to plants that
botanists differentiate between narrow, shallow, and deep crevices when
studying this phenomenon. Narrow crevices will support dwarf goldenweed
or hairy goldaster. Shallow crevices support scabland penstemon,
fernleaf fleabane, and gland cinquefoil. Deep crevices give rise to
syringa, ferns, bush rockspirea, tansybush, Lewis mockorange, and even
the limber pine tree. Complete soil cover and then vegetative cover can
develop on these lava flows only after crevices have first become filled
with soil.
Plants exploit other means of protection to survive in this harsh
environment. Shaded and wind-sheltered, the northern side of a cinder
cone can support grass, shrubs, and limber pine trees while the cone’s
southern face supports only scattered herbs. Most cinder cones in the
park show distinct differences of plant cover between their northern and
southern exposures. Northern exposures are cooler and more moist than
southern exposures, which receive far more direct sunlight. In addition,
here at Craters of the Moon, the prevailing southwesterly winds compound
the ability of the dry heat to rob porous cinder cone surfaces and their
living organisms of precious moisture.
The build-up of successive lava flows has so raised the landscape that
it now intercepts wind currents that operate higher above surrounding
plains. Limber pine trees find footholds on the shaded and sheltered
northern exposures of cinder cones. Bitterbrush and rabbitbrush shrubs
that can barely survive on the lower skirts of a cinder cone’s southern
side may grow two-thirds of the way up its protected northern face. For
many species of plants the limits of habitability on this volcanic
landscape are narrowly defined. Very small variations in their
situations can determine success or failure.
Travelers often ask park rangers whether or not some of the park’s
plants were planted by people. The plants in question are dwarf
buckwheats and grow in cinder gardens. It is their incredibly even
spacing that creates an orderliness that is easy to mistake for human
design. The regular spacing comes about because of the competition for
moisture, however. The root systems of these plants exploit the
available water from an area of ground surface much larger than the
spread of their foliage. In this way, mature plants can fend off
competition by using the moisture that would be required for a
potentially encroaching plant to become established. The effect is an
even spacing that makes it appear, indeed, as though someone had set out
the plants on measured centers.
Craters of the Moon abounds with these surprising plant microhabitats
that delight explorers on foot. The bleak lava flows separate these
emerging pockets of new life, isolating them like islands or oases
within their barren volcanic surroundings.
Scientists have studied Carey Kipuka, an island of plantlife in the most
southern part of the park, to find out what changes have occurred in the
biologic community. _Kipuka_ is a Hawaiian name given to an area of
older land that is surrounded by younger lava flows. Recent lava flows
did not overrun Carey Kipuka, so its plant cover is unaltered. Shortage
of water protected it from livestock grazing that might have changed its
character. Its vegetation is a benchmark for comparing plant cover
changes on similar sites throughout southern Idaho.
For the National Park Service and other managers of wildlands,
kipukas—representing isolated and pristine plant habitat unchanged by
human influence—provide the best answer that we have to the important
question, “What is natural?” Armed with a satisfactory answer to that
question, it is possible to manage the land ecologically. Park managers
can seek to restore natural systems and to allow them to be as
self-regulating as possible. It is ironic that Craters of the Moon, a
volcanic landscape subjected to profound change, should also protect
this informative glimpse of what remains unchanged.
[Illustration: _From the park’s mazes of jumbled rock, ground
squirrels fashion homes with many entrances and exits. Opportunistic
feeders on vegetable matter, these engaging rodents fall prey to
hawks and owls from above and small predatory mammals on the ground.
They therefore serve as an important transfer point between plant
and animal layers of the park’s food energy scheme._]
[Illustration: _In the 1920s, members of the Limbert Expedition,
described on pages 50 and 51, followed the flight of doves to locate
water as they explored what later became the park._]
(_continued on page 46_)
Wildflowers
Wildflowers carpet Craters of the Moon’s seemingly barren lava fields
from early May to late September. The most spectacular shows of
wildflowers come with periods of precipitation. In late spring,
moisture from snowmelt—supplemented now and then by rainfall—sees the
blossoming of most of the delicate annual plants.
Many of the park’s flowering plants, having no mechanisms for
conserving moisture, simply complete their life cycles before the
middle of summer. This is particularly true of those that grow on the
porous cinder gardens into which moisture quickly descends beyond
reach of most plants’ root systems.
As summer continues and supplies of moisture slowly dwindle, only the
most drought-resistant of flowering plants continue to grow and to
bloom. With the onset of autumn rains, only the tiny yellow blossoms
of the sagebrush and rabbitbrush remain.
[Illustration: _Blazing star_]
[Illustration: _Monkeyflower_]
[Illustration: _Desert parsley_]
[Illustration: _Wild onion_]
[Illustration: _Bitterroot_]
[Illustration: _Paintbrush_]
[Illustration: _Scabland penstemon_]
[Illustration: _Arrow-leaved balsamroot_]
[Illustration: _Scorpionweed_]
Mule Deer
[Illustration: {uncaptioned}]
Brad Griffith could be called the mule deer man. In 1980, this
wildlife researcher began a three-year study of the mule deer herd
that summers in the park. The immediate concern was that the deer,
protected inside the park, might be overpopulating their range and
endangering their habitat. Griffith set out to find out just how the
deer use the area, what their population level is, and how certain
factors—production, mortality, and distribution—affect their
population dynamics. The mule deer use the park April through November
only, because winter brings snows too deep for the deer to find food
here. The most striking finding of Griffith’s research is that the
mule deer at Craters of the Moon—unlike mule deer studied
elsewhere—have a dual summer range. Put simply, the mule deer have had
to undergo behavior modification to live here. The deer move back into
the southern park in mid-April, living in the protected wilderness
area there. While in the wilderness area, the park’s deer routinely
live up to nearly 10 miles from open water, getting their water from
food, dew, fog, and temporary puddles. This area has higher quality
forage for these deer than any other part of their annual range. The
trade-off is that the wilderness area has almost no open water. When
the moisture content of their forage decreases in summer, usually in
July, the deer move up to the northern part of the park where there is
open water. Their habits in the northern part of the park are unusual,
too, Griffith says, because there the deer live in much closer
quarters than other herds are known to tolerate on summer ranges. They
live in this wildlife equivalent of an apartment complex until the
fall rains come. Then they move back down to the wilderness area. The
deer make this unusual summer migration, Griffith suggests, to avail
themselves of the high quality forage in the southern park. “The park
serves as an island of high quality habitat for mule deer,” he wrote
in his report. It is now known the deer will leave the wilderness area
for the northern park after 12 days with daytime highs above 80°F and
nighttime lows above 50°F in summer. “We can’t really predict this,”
Park Ranger Neil King says, “but the deer know when this is.” What is
happening is that the percentage of water in their forage plants falls
below what is necessary to sustain the deer with increasingly hot
weather. As you would expect, does nursing two fawns leave a couple
days earlier than does with only one fawn. The rate at which their
fawns survive to the fall of the year is astonishing. “This is an
incredibly productive herd,” Griffith says, “right up there with the
highest fawn survival rate of any western mule deer herd.” Park
rangers continue Griffith’s studies by taking deer census counts.
[Illustration: {Map showing fall, summer, and spring migrations}]
[Illustration: _The Northern Shoshone regularly passed through the
Craters of the Moon area on their annual summer migration from the
Snake River to the Camas Prairie, west of the park. They took this
journey to get out of the hot desert and into the cooler mountains.
There they could gather root crops and hunt marmots, jackrabbits,
porcupines, and ground squirrels. As they passed through today’s
park, they left behind arrowheads, choppers, and scrapers and built
stone circles that may have been used for ceremonial purposes. These
artifacts and structures are evidence the Indians were temporary
visitors to this vast volcanic landscape._]
Indians, Early Explorers And Practicing Astronauts
Not surprisingly, archeologists have concluded that Indians did not make
their homes on this immense lava field. Astronauts would one day trek
about Craters of the Moon in hopes that experiencing its harshly alien
environment would make walking on the moon less disorienting for them.
No wonder people have not chosen to live on these hot, black, sometimes
sharp lava flows on which you must line the flight of doves to locate
drinking water.
Indians did traverse this area on annual summer migrations, however, as
shown by the developed trails and many sites where artifacts of Northern
Shoshone culture have been found. Most of these archeological sites are
not easily discerned by the untrained eye, but the stone windbreaks at
Indian Tunnel are easily examined. Rings of rocks that may have been
used for temporary shelter, hunting blinds, or religious purposes,
numerous stone tools, and the hammerstones and chippings of arrowhead
making are found scattered throughout the lava flows. Some of the
harder, dense volcanic materials found here were made into crude cutting
and scraping tools and projectile points. Such evidence suggests only
short forays into the lavas for hunting or collecting by small groups.
The Northern Shoshone were a hunting and gathering culture directly
dependent on what the land offered. They turned what they could of this
volcanic environment to their benefit. Before settlement by Europeans,
the vicinity of the park boasted several game species that are rare or
absent from Craters of the Moon today. These included elk, wolf, bison,
grizzly and black bear, and the cougar. Bighorn sheep, whose males sport
characteristic headgear of large, curled horns, have been absent from
the park since about 1920.
Military explorer U.S. Army Capt. B.L.E. Bonneville left impressions of
the Craters of the Moon lava field in his travel diaries in the early
1800s. In _The Adventures of Captain Bonneville_, which were based on
the diaries, 19th-century author Washington Irving pictures a place
“where nothing meets the eye but a desolate and awful waste, where no
grass grows nor water runs, and where nothing is to be seen but lava.”
Irving is perhaps most famous for _The Legend of Sleepy Hollow_, but his
_Adventures_ is considered a significant period work about the West and
provided this early, if brief, glimpse of a then unnamed Craters of the
Moon.
Pioneers working westward in the 19th century sought either gold or
affordable farm or ranch lands so they, like the Northern Shoshone,
bypassed these lava wastes. Later, nearby settlers would venture into
this area in search of additional grazing lands. Finding none, they left
Craters of the Moon substantially alone.
Early pioneers who left traces in the vicinity of the park did so by
following what eventually came to be known as Goodale’s Cutoff. The
route was based on Indian trails that skirted the lava fields in the
northern section of the park. It came into use in the early 1850s as an
alternate to the regular route of the Oregon Trail. Shoshone Indian
hostilities along the Snake River part of the trail—one such incident is
memorialized in Idaho’s Massacre Rocks State Park—led the emigrants to
search for a safer route. They were headed for Oregon, particularly the
Walla Walla area around Whitman Mission, family groups in search of
agricultural lands for settlement. Emigrants traveling it in 1854
noticed names carved in rocks and trees along its route. It was named in
1862 by travelers apparently grateful to their guide, Tim Goodale, whose
presence, they felt, had prevented Indian attacks. Illinois-born Goodale
was cut in the mold of the typical early trapper and trader of the Far
West. He was known to the famous fur trade brothers Solomon and William
Sublette. His name turned up at such fur trade locales as Pueblo, Taos,
Fort Bridger, and Fort Laramie over a period of at least 20 years.
After the discovery of gold in Idaho’s Salmon River country, a party of
emigrants persuaded Goodale to guide them over the route they would name
for him. Goodale was an experienced guide: in 1861, he had served in
that capacity for a military survey west of Denver. The large band of
emigrants set out in July and was joined by more wagons at Craters of
the Moon. Eventually their numbers included 795 men and 300 women and
children. Indian attacks occurred frequently along the Oregon Trail at
that time, but the size of this group evidently discouraged such
incursions. The trip was not without incident, but Goodale’s reputation
remained sufficiently intact for his clients to affix his name to the
route. Subsequent modifications and the addition of a ferry crossing on
the Snake River made Goodale’s Cutoff into a popular route for western
emigration. Traces of it are still visible in the vicinity of the park
today.
Curiosity about this uninhabitable area eventually led to more detailed
knowledge of Craters of the Moon and knowledge led to its preservation.
Geologists Israel C. Russell and Harold T. Stearns of the U.S.
Geological Survey explored here in 1901 and 1923, respectively.
Taxidermist-turned-lecturer Robert Limbert explored the area in the
early 1920s. Limbert made three trips. On the first two, he more or less
retraced the steps of these geologists. On his third and most ambitious
trek, Limbert and W. L. Cole traversed what is now the park and the
Craters of the Moon Wilderness Area south to north, starting from the
nearby community of Minidoka. Their route took them by Two Point Butte,
Echo Crater, Big Craters, North Crater Flow and out to the Old
Arco-Carey Road, then known as the Yellowstone Park and Lincoln Highway.
These explorations and their attendant publicity in _National Geographic
Magazine_ were instrumental in the proclamation of Craters of the Moon
as a national monument by President Calvin Coolidge in 1924.
Since Limbert’s day, astronauts have walked both here and on the moon.
Despite our now detailed knowledge of the differences between these two
places, the name—and much of the park’s awe-inspiring appeal—remains the
same. It is as though by learning more about both these niches in our
universe we somehow have learned more about ourselves as well.
[Illustration: _In the mid-1800s the Oregon Trail served as a major
route to the West for pioneers. But when hostilities developed along
the trail with the Shoshone-Bannock Indians, many of the emigrants
began using an alternate route known as Goodale’s Cutoff. This trail
went further north and passed through the present-day park
boundary._]
(_continued on page 52_)
Early Explorers and the Limbert Expedition
[Illustration: {uncaptioned}]
The first known explorations of these lava fields were conducted by
two Arco, Idaho, cattlemen in 1879. Arthur Ferris and J.W. Powell were
looking for water for their livestock. The first scientific
explorations were carried out by Israel C. Russell, surveying the area
for the U.S. Geological Survey in 1901 and 1903. Beginning in 1910,
Samuel A. Paisely, later to become the park’s first custodian, also
explored these lava fields. In 1921, the U.S.G.S. sent two geologists
here, Harold T. Stearns and O.E. Meinzer, with a geologist from the
Carnegie Institute. Based on this field work, Stearns recommended that
a national monument be created here. Also during the early 20s, the
explorations of Idaho entrepreneur Robert W. Limbert caught the
public’s fancy. A report of the explorations of “Two-gun” Bob Limbert
was published in the March 1924 _National Geographic Magazine_.
Limbert was a Boise, Idaho, taxidermist, tanner, and furrier. He was
also an amateur wrestler and quick-draw artist who later performed on
the national lecture circuit. Reportedly, Limbert once challenged Al
Capone to a pistol duel at 10 paces. Evidently Capone declined.
Limbert made three treks into the lava fields between 1921 and 1924.
He first explored the more easily accessible northern portion of the
lava fields. Limbert’s third expedition crossed the area from south to
north, however, starting from Minidoka.
The Limbert Trek
[Illustration: _On his third expedition, Limbert, Cole, and a dog
traversed the lava flows from south to north. The photos that
appeared in_ The National Geographic Magazine _in 1924 were taken on
various expeditions._]
With Limbert were W.L. Cole and an Airedale terrier. Taking the dog
along was a mistake, Limbert wrote, “for after three days’ travel his
feet were worn raw and bleeding.” Limbert said it was pitiful to watch
the dog as it hobbled after them. The landscape was so unusual that
Limbert and Cole had difficulty estimating distances. Things would be
half again as far away as they had reckoned. In some areas their
compass needles went wild with magnetic distortions caused by high
concentrations of iron in the lava rock. Bizarre features they
found—such as multi-colored, blow-out craters—moved Limbert to write:
“I noticed that at places like these we had almost nothing to say.”
Limbert and Cole discovered ice caves with ice stalactites. They found
water by tracking the flights of mourning doves. They found pockets of
cold water (trapped above ground by ice deposits below the surface)
covered with yellowjackets fatally numbed by the cold. They drank the
water anyway. In desert country, said Limbert, one can’t be too picky.
Between Limbert’s lively article in the _National Geographic
Magazine_, and the reports of geologist Stearns, President Calvin
Coolidge was induced to designate part of the lava fields as Craters
of the Moon National Monument on May 2, 1924.
[Illustration: {untitled}]
[Illustration: {untitled}]