(courtesy of Google Earth)The Emperor Seamount and Hawaiian Island Chain are a geologically peculiar archipelago in the middle of the Pacific Ocean that lies thousands of miles away from any tectonic plate boundary or continent. This chain of volcanic islands are among the most geographically isolated places on earth.
The current paradigm suggest theformation of the Chain was caused bythe “hot spot” it sits atop. A hot spot isan area deep within the earth‟s interiorthat erupts Molten rock from beneaththe ocean floor. Over time, volcanicgasses and basaltic lavas from theeruptions build to sea level andcontinues the process upwards,gradually forming a volcanic island.eventually the Pacific plate functions asa conveyor belt and carries each island-volcano northwest from the hot spot atan estimated 4 inches per year. Theisland of Hawai‟i, or “The Big Island”is still under-going this process, beingthe only island on the archipelago that A diagram of the Hotspot (USGS)currently sits on the hot spot, aside fromthe submarine Lo‟ihi seamount.
Unlike the volcanoes we‟re accustomed to seeing here at home, the volcanoes of Hawaii are gently sloped with wide summits – think „naturally-occurring Tacoma Dome‟ . Because of the high-temperature magma of the hot spot, the chemical composition of these eruptions are fluid often allowing lava flows to go on for years at a time. This long, gradual process of erupting builds the gentle slopes of lava around the magma vents. Classification of shields are determined by the distance of the flows around the vents, if the flows are only a few miles across they‟re considered lava shields, examples of these from the trip are Mauna Iki and Mauna Ulu. If the mounds span more than a dozen-or-so miles, they‟re called Shield Volcanoes.Mauna Loa and Kilauea are the youngest and most active volcanoes on the archipelago. These are two classic examples of shield volcanoes. Mauna Loa, with an estimated volume of up to 19,000 cubic miles beginning at its depressed seafloor base is the largest volcano on earth in terms of mass. The slopes of these volcanoes are littered with volcanic features such as lava shields and cinder cones that formed during single eruptions from the magma chamber. Like most geologic features, shield volcanoes go through long stages of formation and de- formation. The three phases are the first alkalic stage, where small volumes of basaltic lavas form, the second is the Shield Mauna Loa’s gentle slopes Building stage, where large volumes of thoeleiitic basalt build, and finally the Second Alkalic stage where the basalt is once again alkalic with low volume. Because the location of The Big Island relative to the Hot Spot, these young volcanoes are still amidst the early building stages. Mauna Kea, Hawaii‟s tallest mountain (above sea level) is in the Late Second Alkalic stage.
Shield Volcanoes are essentiallyhuge unstable piles of basalt thatspread over time under their ownmass. During the spreading process,fracturing occurs on the flanks ofthe volcanoes and often allowsmagma to encroach into the flanks,often causing eruptions far from thesummit of the volcanoes. Theseareas of the volcano are called riftzones. Shield volcanoes like Mauna An aerial view of Mauna Loa’s northeast rift. (J.P. Lockwood, USGS)Loa usually have three rift zones,but younger volcanoes like Kilauea– that builds on the eat rift ofMauna Loa has only two rift zones.
Cinder Cones usually form during the second alkalic stage of shield volcanism. They form when there are axial cracks on the surface of tumuli that allow magma to escape from their vents. They have the physical appearance of classic volcano imagery we all saw growing up, but on a smaller scale. These structurally-weak volcanic Three cinder cones at Mauna Kea’s summit features usually erupt only once in their lives, when the last of the volcanic gases escapes their craters.
When lava first erupts from a magma vent it is usually very fluid with low viscosity. As it travels down slope, the physical properties may change based on the speed of the flow and/or the terrain it travels across. As it travels downward, the lava‟s temperature cools and subsequently gains density. Although the flow comes from the same source, physical properties like gas content of the magma, temperature and rate of travel ultimately determine what type of lava it becomes. We saw two different types of flows, pahoehoe and a‟a, which I have described above (respectively). A field drawing of two lava flows off Saddle Road
Pahoehoe lava has a smooth physical appearance, runs fluidly and can be classified into three different types: entrail, ropy and shelly. These three types of pahoehoe are classified by their texture.Entrail pahoehoe forms when pahoehoe toes travel at a relatively quick rate down slope. To entrail identify entrail pahoehoe, look for a flow with a thick, furrowed appearance. As the pahoehoe flow moves down slope, it gains viscosity and may form a plastic-like coat that allows lava to continue flowing beneath it. When this happens, the Pahoehoe ropy may form a coil-like structure due to the traveling lava, we call this type ropy pahoehoe. As the pahoehoe solidifies, it may also display a cracked, turtle shell-like texture, this type is known as shelly pahoehoe shelly
Unlike pahoehoe, a‟a is a type ofbasaltic flow that has a rough, jaggedsurface with a dense interior full of gasbubbles. It forms when thick, coolerlava breaks apart as it travels downslope. This picture of Amanda meditating on Pahoehoe is a great shot to differentiate the two different types of flows. Pahoehoe being the lighter gray basalt, and a’a the darker reddish basalt.
Lava tubes come in all shapes and sizes. On the trip we explored the depths of two massive lava tube caves and also observed several that ranged from a few inches to several feet in diameter. Lava tubes start as any other flow channel, as the lava cools the outside margins begin to solidify, the hardening process eventually forms a roof structure and unlike most flows that harden completely, these flows leave a core of flowing lava that is surrounded by the margins. Once the flow has run its course, the lava channel empties leaving a hollow tube, similar to if you were drinking out of a straw that had walls formed by a margin of your hardened beverage. Inside of a bigger lava tube
When lava travels through woodedareas or forests, most of the treesbecome engulfed by fire, butsometimes, moisture-rich woods insome trees may cool the lava thatsurrounds it. As the flow graduallyrecedes, the hardened lava thatsurrounds the tree remains, leaving a Lava treecast around the tree. The layer of lavathat encompasses the tree inhibitsfurther growth and eventually kills it,but the hardened pillar remains, makingit a lava tree.In a case where the lava flow continueswithout receding the area, trees maybecome overpowered by the flow. Overtime, the trunk may decay and leave avertical, well-like tube that we call a Tree moldtree mold.
A caldera is a sunken depression atthe top of volcanoes. Calderas canoccur as either of the following:Explosive calderas are the outcomeof an outward explosive eruptionfrom avolcano, Crater Lake inOregon is an example of this.Collapsed calderas are pit craterson a larger scale. As lava lakes aredrained from underground anderuptions occur, sunken orcollapsed summits may result dueto the weight of the edifice.Kilauea Caldera, a 2.5 by 2-milecaldera that is currentlyexperiencing activity within its Halemaumau crater within Kilauea Calderalimits at the Halemaumaucrater,was a collapsed crater that we sawon the trip.
There are two different types of craters, explosion craters and pit craters.Pit craters are formed by tensional stress caused by the recession of magma, resulting in the upper-most crust sinking and collapsing into the receded area beneath, creating a scarp. In contrast, explosion craters form when a subterranean explosion occurs and erupts debris or tephra from the source. Mauna Ulu Crater
Faults are abrupt fractures in a volume of rock that has undergone significant displacement. When energy is released from fault systems, seismic activity usually occurs. During the trip, we studied the Koa‟e fault zone with renowned geologist Don Swanson of Hawaii Volcanoes Observatory. The Koa‟e fault zone is an area that connects Kilauea‟s southwest and east rift zones. Seismic activity at Koa‟e is caused by the massive weight of Kilauea Volcano and has been home to earthquakes that have left cracks up to 80 meters deep in some places. This area is known as one of the world‟s most active fault zones.
A scarp, or “pali” in Hawaiian, is an expression of faulting as a result of activity or fault movement that causes structural displacement. Scarps contain fractured rocks and can be very steep. HoleiPali slump scarp is a type of fault landslide that drops debris into the ocean and can cause a tremendous threat that I will talk more about in the Hazards section of the project.
Within this fault zone lies an areaknown as White Rabbit, named after a1960s song by the psychedelic bandJefferson Airplane. This fault is one ofKoa‟e‟s numerous thrust fault scarps.White Rabbit is a 2.5 km-long fault thatfaces uphill towards Kilauea‟s summitand is a continuation of the east rift. Thelast major faulting event was anearthquake that took place on ChristmasEve 1965 that caused an 8 foot verticaloffset of a 500-700 year-old flow.
Ring faults are circular fractures that develop around emptied magma chambers. Kilauea Caldera is surrounded by a circumferential ring fault that also functions as a binding for Kilauea‟s southwest and east rifts Part of Kilauea caldera’s circumferential ring fault system
Steam vents are series of roughly parallel vents that are caused by shallow sources of magma (1 kilometer or less) that steams groundwater from below the ground‟s surface.Sulfur banks are the result of deep faults extending down to the magma layer where volcanic gasses seep from the Sulfur vent ground when mixed with the groundwater steam. The sulfuric gasses are rich with hydrogen sulfide, carbon dioxide and sulfur dioxide. Green crystal deposits and a brownish to red clay substance are known to form around the surface of the vents due to the released gasses from the steam. Steam vent
Being a resident of Hawaii may bea dream to some people, but itdoesn‟t come without its fair shareof risks.Because Hawaii is essentially ahuge chain of either inactive oractive volcanoes, obvious volcanicrisks like explosive eruptions, lavaflows, towering lava fountains andthe release of dangerous volcanicgasses may occur.Other other dangers such asearthquakes and tsunamis are also A former part of Chain of Craters Road wheremore likely to occur in Hawaii than a Pahoehoe flow took overother places in the world, creating ahazardous environment for all of itsinhabitants, not just humans.
Volcanic eruptions may come in several forms. A lava fountain, like the one that occurred at Kilauea Iki, is a visually astounding eruption that spews lava thousands of feet into the air.I‟ve discussed lava flows, a slow-moving eruption that occurs often in on the island of Hawaii. The two types of eruptions I‟ve listed above can be easily monitored and their vicinities can be evacuated to avoid potential hazards to life. Explosive Eruptions To be considered an explosive eruption, there needs to be a form of tephra, airborne lava fragment, erupted into the air. Explosive eruptions in Hawaii are believed to An explosive eruption at Kilauea occur due to groundwater coming into contact with magma and creating steam. This tremendous force of steam can cause an eruption if a present lava lake recedes below the water table and collapses, allowing the built-up pressure of the steam to escape in the form of an eruption.
Pele’sHair Ash In-order from smallest to Lapilli largest, tephra comes in all shapes and sizes. Pele‟s hair Cinders is different among most other units because of its hair-like appearance. Blocks Bombs
Organizations like the U.S. Geological Survey‟s Hawaiian Volcano Observatory monitors volcanoes and earthquakes to observe patterns of past, current and future eruptions and study the process of the activity. Monitoring of ground and volcanic activity includes real-time video (HVO courtesy of USGS) capture, seismometer testing, tiltmeter recordings, GPS mapping and sample-taking.
The most common rock type found in Hawaii is the igneous basalt. Basalts are usually dark, fine-grained in texture, and are extrusive. Basalt is a rock that forms when lava cools and solidifies and is common throughout the world, but seen everywhere in Hawaii because of the islands‟ volcanic make- up.TheBlack Sand Beach (Punaluu Harbor) was produced by the rapid cool down of a volcanic explosion, causing the fine black sand debris.
The most common mineral observed on the trip was olivine. This magnesium iron silicate crystallized from magnesium-rich magmas that are low in silica. The olivine we saw in Hawaii were always features on basalt, a mafic rock, but can also occur in ultramafic rocks like peridotite.The Green Sand Beach of The Big Island gets its name from the greenish color of the sand there that is caused by eroded olivine from basalt. Under the magnifying glass, I saw that the sand appeared to have an 80 – 90% olivine content, a much higher level than in previous years.
PumiceIs a lightweight highly-pressurized volcanic rock that is created by rapid magma eruptions. Reticulate Reticulate gets its name from the hexagonal shape of its holes. It is a type of pumice that is found only at volcanoes that erupt basalt. It has a soft spongy texture with a 98% Part of a CE ~1500 reticulate layer at Kilauea bubble content
Rain shadow Elevation Zones Most of Hawaii‟s rainfall comes Hawaii has six distinct from windward trade winds while elevation/vegetation zones that the leeward flanks stay relatively include (from sea level): dry. This makes for an enormously 1. lowlands diverse climate for an island of its 2. mid-elevation woodlands size. 3. rainforest 4. upland forests and woodlands 5. subalpine 6. alpine/aeolian (Courtesy of NOAA Climate Services)
Succession Succession is an ecological process by which a community sees changes over time, then progressively forms into a stable community. Succession is often triggered by geologic catastrophes like eruptions, earthquakes or tsunamis. Primary succession is when a former landscape is destroyed and there are little to no living organisms left behind. In Hawaii, Primary succession is common because of its highly active volcanoes. Secondary succession is when an environment is disturbed, but not obliterated like an environment that Kipukas are islands of older lava that have been would undergo primary succession. In surrounded by more recent flows. Primary succession secondary succession, living organisms surrounds this particular kipuka. can remain, but in smaller numbers. A forest fire is a leading example of a cause for secondary succession
Hawaii‟s rich cultural history began when Polynesian rigger canoes first arrived on the islands around CE 500. These settlers brought with them most of Hawaii‟s trademark tropical plants, animals and a rich tradition of agroforestry and farming.Hawaiians are known to have always revered their natural surroundings, especially the islands‟ volcanic features. Pele, the A painting of Pele at Jaggar Museum Hawaiian goddess of volcanoes is said to live within Kilauea caldera, where she often shows her magnificence through displays of eruptive power.Reverence was also displayed through rock carvings, known as petroglyphs, near the shore where new mothers were believed to have gave their newborns umbilical cords as an offering of unity with nature and their family. Hawaiian petroglyphs
Google Earth. Web. 10 Oct. 2011. <http://earth.google.com/>.Hazlett, Richard W., and Donald W. Hyndman. Roadside Geology of Hawaiʻi . Missoula, MT: Mountain Pub., 1996. Print.Stone, Charles P., Linda W. Pratt, and Danielle B. Stone. Hawaiis Plants and Animals: Biological Sketches of Hawaii Volcanoes National Park. Honolulu, HI: Hawaii Natural History Association, 1994. Print.USGS Hawaiian Volcano Observatory (HVO). Web. Oct. 2011.<http://hvo.wr.usgs.gov/>.