The Professional Study of Hawaiian Volcanoes

A number of factors recommended Hawai‘i for specific research. Its volcanoes are eminently accessible. They are frequently active. And they are not so explosive that studying them puts scientists in physical danger. Many professional and lay volcanologists visited and studied the Hawaiian mountains throughout the 1800s, and detailed surveys were performed as early as the 1870s under the Hawaiian monarchy. But it wasn’t until 1911 that the first permanent observatory was built. In that year, Massachusetts Institute of Technology scientist Thomas Jagger and volcanologist Frank Perret established themselves at the rim of Halema‘uma‘u. The Hawaiian Volcano Observatory was founded the next year with funding from both MIT and Hawai‘i business officials. The work often involved active inventing, since equipment and techniques were required that no one ha ever before envisioned.

Jaggar recognized the uniqueness of Hawai‘i’s volcano country, and joined in an effort to get the area named a national park. Kilauea and the summit of Mauna Loa were included in a park established in 1916. The first observations of the volcano had been purely visual. But the arrival of scientists pushed the development of new measuring devices. Early thermometers were simple mixtures of materials that melted at different temperatures, which were inserted into the lava to get a rough idea of the heat of the molten rock.

With time and improved technology, the equipment got more sophisticated. By the 1940s, scientists still led by Jaggar were measuring a variety of volcanic phenomena that had been unknown just a few decades earlier.

Studying Kilauea

Even better technology in the 1950s allowed volcano scientists to link their distant measuring stations to the central observatory site at Kilauea’s rim. With the more sensitive equipment they could not only track earth movements, which sometimes suggested underground movement of magma, but also measure which areas were swelling and perhaps getting ready to erupt. Scientists followed the Kilauea eruption of 1955 on the lower east rift zone and the Kilauea Iki eruption of 1959, which sported huge lava fountains that people could drive to. The visual displays were dramatic but probably more interesting to the volcano scientists was using the new sophisticated equipment to study the swelling and subsiding of various parts of the summit as magma moved underground up and down, and back and forth.

In 1960, the volcano erupted next to the rural village of Kapoho. After its flows rumbled through the agricultural fields and burned home after home, all that remained was the old lighthouse at Cape Kumukahi. Following more than a dozen eruptions during the 1960s, Kilauea entered a new kind of activity; the continuous eruption of Mauna Ulu lasted five years and shifted back and forth on the rift zone, forming shield and steep-sided cones. It sent lava flows down the side of the mountain and into the ocean, forming platforms of new solid land.

Studying Mauna Loa

During the 60s the Island of Hawai‘i’s other major attraction was quiet. Mauna Loa had erupted fro 23 days in 1950, then kept its peace for 25 years, ending with a one-day eruption at the summit crater of Moku‘aweoweo in 1975 and again in 1984. Later on the same day it kicked off a new vent at an elevation of about 9,000 feet on its northeast rift zone, with high fountains in the chill mountain air. The eruption continued for three weeks, sending a long flow down the slop toward Hilo. The ribbon of black and orange lava extended for miles, but its leading edge was blocked just four miles short of Hilo. As a result, the flow broke out of the channel and sent a new flow parallel to the old one, reaching a little closer to Hilo. That channel became clogged again, and a third flow headed down slope. But by then, eruption was dropping off. On its 22nd day, it stopped.

Yet for months prior to this, Kilauea had also been active. The Mauna Loa eruption answered one question volcano observers had debated for years: could two volcanoes erupt at once, or was there a single feeding route that pumped magma to one or the other, but not both? There had been overlapping eruptions of Kilauea and Mauna Loa in 1919, although few people were aware of it. Chemical studies of the mineral and gas content of the lavas from the 1984 eruptions concluded that individual volcanoes have no connection near the surface, even though they ultimately all get their magma from deep within the same hot source in the mantle.

Kilauea’s Long One

For more than a century, from 1823 to 1924, Kilauea maintained a nearly continuous lava lake. But until Mauna Ulu’s eruption between 1969 and 1974, modern era observers had not seen anything like an eruption that poured rock continuously down the slope of the volcano. For years on end, it covered existing countryside, raised the elevation of the slope and built up new land at the seashore. Mauna Ulu sent its lavas southward down the Kilauea east rift zone over undeveloped land. The new rock covered parts of the Chain of Craters road and many archaeological sites on its way to the ocean, but no homes where threatened.

Than all the activity stopped and Mauna Ulu seemed to be an anomaly. That perception changed a decade later when in 1983 another east rift zone eruption of Kilauea began that went on, and on. It was centered 12 miles out from caldera, a long running eruption that set a new standard.

Volcano science was now more advanced than for any previous Kilauea eruption. Sensors detected magma movement even before eruptions occurred. Tiltmeters measured the expansion and contraction of the summit and rifts of Kilauea. As the eruption continued, new technologies were added to the geologists’ tool boxes. Global positioning system satellite receivers, which became commonplace during the eruption, could measure with incredible accuracy the movement of the earth around the volcano. The result was that the eruption of Kilauea that started in 1983 is probably the best-studied volcanic activity in the history of the planet.

The eruption began, as many do, with a subsurface rumble. The sophisticated seismic system , with its heart at the Hawaiian Volcano Observatory headquarters on the edge of Kilauea’s caldera, recorded swarms of earthquakes. These indicated that magma was moving deep underground and pushing into new channels creating a path for itself by ripping the rock apart. Just after midnight, the earth opened up at Napau Crater and fountains of orange lava danced into the night sky. The eruption spread up and down the east rift zone of Kilauea, to Pu’u Kamoamoa, on to Pu’u Kahauale’s and back to Pu’u Kamoamoa. After ten hours the fountaining stopped briefly, but resumed with a 200-foot-high curtain of lava.

New Fountains

Scientists continued to measure the activity that occurred underground. On January 6, there were more fountains at Pu’u Kahauale’a and Pu’u Kamoamoa. The next day that activity went on and Pu’u Kalalua was added to it. Now, the eruption settled in, and lava began pooling and then spilling off the side of the mountain in a glowing flow.

The Kalapana coastline, downslope of Kilauea’s east rift zone, was not heavily populated. The Royal Gardens subdivision had roads but the developers had provided little else; no phones, water lines, electricity. Its network of paved roads headed steeply up the slope of the volcano. The 1,500 lots were on acre each, but most lacked any kind of structure. About 50 had some variety of building on them, often very simple, rustic homes for total of 150 people or so. The first flows headed directly toward the subdivision. More than half the residents were evacuated, but the lava stopped, and the moved back.

Volcanic Fumes

People living downwind in the South Kona area began feeling the discomfort living next door to an ongoing eruption. The volcanic fumes made their eyes water, and caused worsening health problems for those with respiratory ailments. Acid rain damaged vegetable and flower crops. Smoke from forest fires further degraded the air quality.

Flows continued to start and stop; some were the slower-moving pahoehoe, appearing fluid and with a smooth surface that often had a ropelike texture; ‘a’a flows tended to be thicker, with a leading edge of broken rock called clinker. On March 2, the first building burned as an ‘a’a flow rolled in on Queen Avenue in Royal Gardens. A house-trailer burned right after it, the first home lost to lava flows since the Kapoho eruption in 1960.

Within four months a quarter of the subdivision’s empty lots were covered in black lava and eight buildings were reduced to ashes. By the end of the year, another eight had been destroyed.

The eruption now appeared to by centered and was creating a new cone. It was near the printed letter “o” on some maps that geologists used. After consulting with the Hawaiian community, the vent was named ‘O’o, and the cinder cone Pu’u ‘O’o, after a native bird of the forests, those feathers were used for the capes of chiefs. Elders differed over the exact meaning; some preferred ‘o’o the name of the bird, while others argued for o’o, meaning completed, or matured.

The eruption went on in episodes; dramatic activity with towering fountains, then pause, then more eruption. Scientists gave each episode a new number. But since the magma appeared to be using the same underground channel to feed each eruption, and since the lava emission occurred in the same limited complex of vents, it was all considered part of Kilauea’s long one.

Mauna Loa Joins In

In 1984, Mauna Loa erupted as well. The staff at the Hawaiian Volcano Observatory was under tremendous strain to keep track of two eruptions at once. As Mauna Loa sent a long flow northwest toward Hilo, Kilauea ran an entirely new flow northeast toward Hilo, Kilauea ran an entirely new flow southward down the east rift zone to Royal Gardens. Civil Defense officials expanded their areas of evacuation, including a number of homes in the older neighboring community of Kalapana. By mid-April, both Kilauea and Mauna Loa had subsided without destroying any homes. But in the third week of the month, Kilauea made its first entry into an inhabited area outside Royal Gardens.

The most southerly development of the lower Puna coastline was the hillside subdivision of Royal Gardens. Immediately to the northeast, along the coast road, there was the old, predominately Hawaiian rural community of Kapa’ahu. Farther along were the clustered homes of Kalapana, which had both old lots and Kalapana Gardens, a subdivision full of mostly new residents. Beyond that were a few structures around Kaimu black sand beach. The gathering place for residents and the eruption watchers in the region was Kalapana Store and Drive-In, next to the Mauna Kea Congregational Church of Kalapana. Another gathering place was the pavilion and picnic tables of Harry K. Brown Park. All of these areas would suffer a similar fate.

Sites Lost

There were many historic sites in the region, starting with the important Waha’ula Heiau complex, dated at 1275 A. D. In addition the area had Hawaiian village remains, other heiau or temples, canoe landing sites, trails, coastal habitation and refuge caves, the famed clear waters of Queen’s Bath and mush more. It was difficult to walk far without coming across remains of early habitation.

The regular eruptions at Pu’u ‘O’o build up at cone several hundred feet high over lava flows that had raised the level of the surrounding land. By mid-1986, Pu’u ‘O’o was 800 feet higher than the land had been before the eruption. Geologists at the Hawaiian Volcano Observatory recorded 47 different episodes that started in 1983, and in the 3-1/2 years of activity, an estimated 26 million cubic meters of lava had been erupted onto the slopes of an east rift zone.

But now something changed. On July 18, 1986, the eruption abandoned Pu’u ‘O’o and moved to a series on new cracks, creating a mile-long curtain of molten rock. Activity settled in at a location that came to be known as Kapainaha, and stayed there for the next five and a half years. This site was about two miles farther out the rift zone than Pu’u ‘O’o, and put lava more directly uphill from inhabited areas. The Kupaianaha vent sent flow after flow down the mountain. By late November, hot lava was back threatening a coastal village.

Lava Moves

Lava flowing on the surface normally moves fairly slowly unless it is on a steep slope or in lava channel. But a long-lasting flow often creates a lava tube system, which changes the dynamics, especially for people with properties at the far lower end. As a flow moves, its sides and top cool and begin to crust over, while lava continues to flow inside the hardened crusts, creating a long tube, through which the hot molten rock moves without the cooling effects of winds and rain. Lava in these tube systems can be sampled through skylights, which are holes in the tops of the new tubes. Skylights often are formed when pieces of the tube roof collapse. Thus, tubes make it possible for still-fluid, fast-moving, hot lava to be delivered right down to the coast, retaining its destructive capabilities.

In late 1986 lava suddenly poured into the town of Kapa’ahu, destroying eights homes, utility lines and roads. This was a severe blow to the community. While the Royal Gardens subdivision had been mainly occupied by new residents without extensive roots in the region, the people of Kapa’ahu had lived there for generations, raising children and grandchildren in the same wood-frame houses, their favorite plants carefully tended in their yards. The lava flowed through their properties, reached the barrier of the raised Kalapana Highway, and then simply waited while more and more lava backed up behind the highway. Finally, the crusted lava lake was high enough and smoking rock slipped across the tarmac. That flow separated the eastern and western Kalapana coastline. Children in Royal Gardens’ remaining homes had to commute 50 miles through Volcano and Kea’au to get to school in Pahoa. Their neighbors, on the other side of the flow, had just a 10-mile ride. The lava went on, streaming and hissing. On the one hand, the flow poured rock continually into the sea, creating 20 acres of new land within a few weeks. But on the other hand, it followed a path of destruction, inching eastward toward Kalapana. On December 17, the first home was burned, and three days later, 17 more were gone. Many residents were evacuated to a Red Cross shelter in Pahoa, or camped nearer home in Harry K. Brown Park. Those who still had homes were able to spend Christmas there.

Kalapana tried to get back to a normal life. The country ran bulldozers over the still-warm rocks to allow cars to drive along the original rock to the Kalapana Highway, but by the end of March 1987, lava once again crossed the road. Molten rock poured into the historic natural bathing pool Punalu’u, known as Queen’s Bath, which hissed and boiled as the lava crept through. The only remaining Royal Gardens access, a footpath, was covered, and then the flows moved westward toward National Park Service building. In June and July 1989, despite efforts to divert the flows by spraying them with water the tanker trucks, the park’s complex was lost. Thick sheets of lava seeped under the buildings, heating them until they bursting into flame. Afterwards, only iron roofing and metal girders lay on the surface of the flow.

Pali Diversion

In 1990, the activity moved back to the east. There a geological feature helped ensure the final destruction of Kalapana. The Hakuma Pali, a cliff standing between the coast and the village prevented flows from reaching the sea. Instead, they turned left and poured through Kalapana Gardens and old Kalapana Gardens and old Kalapana.

It was the end of the community. To those directly affected, the volcano seemed to be in a single-minded mopping-up mode. Lava oozed this way and that, ultimately engulfing everything. Every single home in Kalapana village was destroyed. Some thought Pele would save the churches. But the Congregational church burned. In a heroic effort, residents and friends hoisted the Painted Church, which was across the road and closer to the beach, and carried it out of harm’s way.

Yet the sense of loss went far beyond just the structures. The peaceful character of the land was altered. As earlier flows had consumed the Queen’s Bath and other prehistoric sites, this series of flows covered Kaimu Bay. Hissing lava flowed into Kalapana surfing areas.
The eruption was nearly continuous from 1986 to 1992, and it created a broad shield, Kupainaha-a new feature on the east rift zone. It produced an estimated 41 million cubic meters of lava. The communities of Royal Gardens, Kapa’ahu and Kalapana were no more. By now, 181 houses had been wiped out, along with the Waha’ula visitor center and innumerable archaeological sites. With the destruction of the buildings, and the departure of the residents, much of the media and public interest in the eruption waned. The eruption was once more less of a people story and more of a geological curiosity. But the volcano kept on.

Vast Destruction

On February 7, 1992, the eruption moved back uprift to Pu’u ‘O’o in what scientists calculated as the long-running eruption’s 50th episode. For curious non-scientists, it was too difficult and dangerous to hike out to the vent, where gasses were toxic and the lava unstable. But a comparatively safe visit could be made to the edge of activity at the shoreline. But a comparatively safe visit could be made to the edge of activity at the shoreline. Visitors frequently took extreme risks and walked over cooling flows to get near where lava was pouring into the sea. The coastal lava benches regularly collapsed, and officials were kept busy trying to control thrill-seekers who did not understand the danger. It was a year-round show that attracted thousands, despite acrid clouds of steam containing hydrochloric acid and sulfur dioxide. At the shoreline, the area covered by lava was almost six miles wide.

Campers Surprised

Local attention continued to be focused on the shoreline through the early and middle 1990s, then a change in upslope activity reoriented public attention. On January 30, 1997, two campers in Napau Crater were awakened by shuddering ground and an unearthly roar. Kilauea had changed sites again. The terrified campers scrambled to safety as the volcano broke through again where the eruption had started back in 1983.

There were several episodes of fountaining, but then Kilauea grew quiet. Three weeks later, some observers began predicting that the flurry of activity had been a last gasp; the eruption could be over. Yet with episodes 55, Pu’u ‘O’o kicked back into gear. At first just some rising and falling of lava deep in the crater itself and the lava lake next to it, but soon the flow of magma to the Pu’u ‘O’o kicked back into gear. At first just some rising and falling of lava deep in the crater itself and the lava lake next to it, but soon the flow of magma to the Pu’u ‘O’o site was re-established, and the eruption was back in familiar territory. No one knew how long it would last.

Mauna Loa

Massive, rising nearly three miles above sea level, and extending another three miles down to the sea floor, Mauna Loa is the biggest volcano on the planet in terms of volume. But its time is passing. Geologists figure the center of Mauna Loa has drifted past the Hawaiian hot spot, though it is still being fed magma. Kilauea, which may be nearly right over the hot spot, is believed to be fed directly, while Lo’ihi is apparently at the leading edge of the hot spot. Both Kilauea and Lo’ihi have formed on the flanks of Mauna Loa, yet are considered to be distinct volcanoes.

Mauna Loa itself erupted 23 times in the past century. Two of these eruptions, in 1940 and 1949, lasted more than 100 days. One in 1903 lasted 60 days, and none of the rest went on for more than 50. Most commonly, the duration was for a week or two. The volcano sent out very fluid lavas, which moved quickly down the slopes. Five flows have reached the ocean since 1868.

Archibald Menzies

The first European to climb Mauna Loa was Archibald Menzies, a famed botanist who visited with Captain George Vancouver in 1793 and 1794. Menzies arranged with the new king. Kamehameha, for a trek up the mountain. It is an indication of how difficult the travel was that he only made it to the summit on his third attempt. In these days of paved roads and high-powered vehicles, it is almost impossible to understand the difficulties faced by early travelers.

The volcanic landscape and the distances on the Island of Hawai’i argued for an initial approach by ocean. Menzies left his ship on a double canoe with 20 paddlers. Their first night was spent at Honaunau, just a short distance down the coast. The next day’s run was a long one, to Honomalino, a small sandy bay where they loaded up on coconuts and spent the night. The sea was rough when they arrived at Manuka for the third night, and the black cliffs and boulders of the coast appeared dangerous. Menzies could not see how they were going to land, but the double canoe’s crew set up just offshore and waited for the right wave.

Perilous Landing

The botanists’s account continues in a tone of amazement: “With this surge they dashed in, landed up on a rock from which we scrambled up the precipice and in an instant about 50 or 60 of the natives at the word of command shouldered the canoe with everything in her, and clambering up the rugged steep, lodged her safety in a large canoe house upon the brink of the precipice, to our utmost astonishment. “They were able to watch as a second canoe was successfully brought ashore the same way.

The dexterity of the Hawaiians in the ocean, even where it crashed onto the rocks, was a matter of fascination to these Europeans. Menzies found it amazing that the native residents were able to convert the rugged landscape into a place for sport. He wrote of daring female cliff divers: “A number of young women…stripped themselves quite naked upon the summit of a pending cliff and taking a short run vaulted one after another from the brink of it headlong into the sea regardless of the foamed and agitated appearance of that element, and as it were setting its wildest commotions at defiance, for at this time the surf ran very high and dashed with furious force against the cliff, yet they dexteriously disentangled themselves and clambering up the rock again, repeated their leaps several times with seeming satisfaction till they were quite fatigued. The cliff was at least thirty feet height and so very rugged with packed rocks which were not and they deluged with a boisterous surf, that to look down the precipice was enough to intimidate any one not accustomed to such extraordinary feats of activity.”

Plantation Hike

The expedition then went on by foot up the southeastern side of the island. They passed through fields of grass, and plantations of bananas, kalo and sweet potatoes. Menzies the botanist made not that in this dry countryside, the natives mulched their cultivated fields with grass “to preserve them from the powerful heat of the sun.”

They passed through Punalu’u and reached Kapalala, where they began a direct route to the summit. Although the eruption records don’t refer to a Kilauea eruption in 1794, Menzies felt there must have been one because of the smoke and ash blowing down the southeast plank. He complained the air was “very thick” and “very tormenting to our eyes.” They headed uphill on February 13 frp, an elevation of 1,800 feet. Menzies used a barometer, using the declining atmospheric pressure that occurs when with rising altitude to calculate his elevation above sea level. By the end of the day they had reached 3,510 feet. The next afternoon, they found frost on the ground. On February 15, they passed the tree line at 10,543 feet, and camped at 11,515 feet. The weather was below freezing, and since they were too high to find wood for a fire, they burned their walking sticks to cook hot chocolate, which they drank with a little rum.

Rum and Coconuts

On the morning of the 16th, 10 days into the expedition, their only remaining provisions were a few coconuts, a little chocolate and part of a bottle of rum. Menzies reached the edge of Mauna Loa’s summit caldera, Moku’aweoweo, just before noon. He calculated its elevation at 13,635 feet, which is just 40 feet short of modern figures. Decades later, observers still made errors of thousands of feet guessing its height. The summit caldera had cliffs 400 yards high, Menzies figured, and was a mile across. The bottom of the caldera was flat, with a rough texture and hot steam rising from two or three places at its edge

The next well-documented climb up Mauna Loa was by another Scottish botanist, David Douglas, who later died in Hawaii under mysterious circumstances. He also went up on the route from Kapapala in January 1834, and had to trudge through deep snow to reach the edge of Moku’aweoweo.

Hawaiian Guides

While these men may have led the first expeditions that include Europeans, it seems clear that they walked in Polynesian footsteps. After all, both were shown the proper route by Hawaiians. It is near the present ‘Ainapo trail, which even today is on of the three main routes to the summit. In 1794’ Ainapo provide the shortest distance to the top from a place where provisions could be acquired at that time.
The first serious surveying trip apparently went up near the present-day Mauna Loa Trail. This ascends from Kilauea along the northeast rift and reaches Moku’aweoweo form the east or northeast, while Menzies and Douglas approached from the southeast. The United States Exploring Expedition, under the command of Lt. Charles Wilkes of the USS Vincenne, headed up in December 1840. The men built a small compound on the mountain, with high wall to break the force of the wind during their stay. Wilkes spent nearly a month there. His choice of routes provides one proof that the Hawaiians knew the way up the mountain: they told Wilkes that he had taken the wrong way, and indeed he had difficulties that could have been avoided. Wilkes nevertheless produced the first surveyed chart of the top of the world’s biggest mountain in terms of height and mass from bottom to top.

Since that time, Mauna Loa has been thoroughly studied. Instruments track every shudder and quake. But hiking the mountain is still an extreme challenge, a four or five day affair, even starting at 6,662 feet at the end of Mauna Loa Strip Road, and even with the help of two cabins, on 7 miles up the trail, and the other 11 miles further on, neat the summit. Travelers still come from all over the world to make the climb.

Lo‘ihi

HAWAII’S YOUNGEST VOLCANO, 20 miles off the southeast coast of Hawai‘i, has its summit still 3,100 feet below the surface of the ocean. Like Kilauea, Lo‘ihi is growing on the (undersea) slope of Mauna Loa, the largest active volcano in the world. Studies of the earthquakes under Lo‘ihi show that the shallower events are near the present location of the volcanic seamount, but down deep the converge with the quakes under Kilauea. Scientists feel this shows that Kilauea and Lo‘ihi are tapping the same magma source, the Hawaiian Hot Spot, as does Mauna Loa. However, studies of the actual rock erupted by the three volcanoes show that it is chemically different. It’s not clear why this is the case.

For a long time, Lo‘ihi lay undiscovered, and even after scientists became aware of it, they weren’t sure it was an active volcano. That changed with improved earthquake monitoring techniques. In 1970, equipment on the Island of Hawai‘i registered a swarm of earthquakes and scientists were able to calculate their location: Lo‘ihi. The volcano has been fairly quiet in recent years, but in July 1996 Lo‘ihi broke into most active swarm of quakes ever measured on any Hawaiian volcano: more than 4,000 within a month.

Deep Submersible

By this time, scientists had the technology to go down and see what was going on. Using a deep submersible vehicle, a specialized submarine, they found the quake of 1996 had left a vast caldera. Not surprisingly, it was shaped much like the one atop Kilauea. Other features of the undersea mountaintop had been obliterated. Scientists believed the magma chamber under the summit suddenly filled underground cracks rather than erupting onto the surface. The earthquakes resulted from shuttering associated with the cracking of rock as magma forced its way up through the ocean floor. The scientists who arrived within days of activity also found it was difficult to see anything because Lo‘ihi was shrouded in clouds and sediment.

All Hawaiian volcanoes begin as submarine volcanoes, and rise as much as three miles before they break the surface of the ocean. Lo‘ihi actually started in somewhat shallow waters, since it already stands on the submerged slope of another volcano. The early eruptions of Hawaiian volcanoes generally can’t be detected by the eye at surface. The pressure of the deep ocean water prevents explosive events, but the volcanoes still erupt, and lava is released. One feature of these eruptions is pillow lava, large mushroom or pillow-shaped extrusions with comparatively smooth surfaces. This undersea rock, which hardens very fast in the cool ocean water, tends to be brittle and glass-like. Submerged volcanoes are torn and shaken by earthquakes just like surface volcanoes, and their appearance can be changed dramatically.
Lo‘ihi is a very steep volcano, much-fractured and thus porous. Sea water is thought to flow readily among its surface rocks. Some geologists also believe that a strong future eruption could produce a huge landslide, large enough to create a catastrophic tsunami. However, like so much speculation about volcanoes, this is an educated guess, a theory that might or might not be valid.

Slides

AS GEOLOGICAL FEATURES, volcanoes are often steep but are not a solid mass. Their rock is extensively fractured, and different portions are subjected to a range of forces, such as gravity or the expansion and contraction of active volcanoes. Sometimes those forces cause sudden movements in the form of deep unfelt earthquakes, measurable only with sensitive equipment. More powerful movements can produce massive changes on land and in the surrounding sea. Just as a motion in a bathtub causes ripples in the water, a movement of land along the coast can cause tsunami, ocean waves that result in extreme damage to shoreline areas many miles away.

You can do a simple experiment to show how many earthquakes occur. Wet your hands, then dry them and press the palms together. Now begin forcing them in different directions. Push the right hand toward the fingers and the left hand toward the wrist. If the hands are dry, but not too dry, friction holds them in place until the pressure grows sufficiently to overcome it. Eventually, your hands slip, then stop, with the fingers of the right hand now overlapping those of the left. The same principles apply for huge land masses.

Quake Falls

In an earthquake two sections of land are forced in different directions by pressures deep in the Earth. Generally at established fault lines, they slip, and the sudden release of energy produces vibrations that travel through the rock, creating an earthquake.

Sometimes such an earth movement can cause dramatic settling and changes in the landscape. A powerful earthquake in 1975 caused a section of volcanic coastline to suddenly subside; at Halape, where the resulting tsunami killed two people, the subsidence left a grove of coconut trees standing in several feet of sea water. Hawaiian traditions record other severe earthquakes that also caused land changes.
But perhaps the most impressive quake-related land movement is a missive event in which a whole section of the island disappears in a giant undersea landslide. Underwater mapping techniques now suggest that there have been many such slides around most of the larg islands. Mapping of the sea floor has located large debris fields, many of them at the bottom of sea cliffs.

Such events must be so huge, and associated with such forceful tsunami, that it’s a good thing no human has seen one. Certain geologists believe evidence of coral and other debris at 900 feet in elevation on the Island of Lana‘i are the result of tsunami associated with a massive Hawai‘i marine avalanche.

Moloka‘i’s Cliffs

Some of the highest sea cliffs in Hawai‘i are on the north coast of east Moloka‘i. Ocean floor mapping shows basalt boulders and other debris extending out 100 miles north of those cliffs.

There is a similar phenomenon on O‘ahu’s north coast, off the steep cliffs that stand mauka of Kane‘ohe and the region on both sides of it. There are slide areas off Kaua‘i and Ni‘ihau as well. In all, scientists have located 15 big slide areas around Hawai‘i’s islands. They consider them to be massive, even on a planetary scale.

 

The big slides provide students of Hawai‘i volcanoes with a remarkable tool. By breaking away sections of land that have been laid down roughly horizontally, they provide a cutaway view of the geological history of the Islands in the form of layer upon layer of old lava flows.
One could reasonably speculate that enormous landslides – large enough to create tsunami – are not a daily threat, particularly on the older islands with dead or dormant volcanoes. Presumably these volcanic slides where huge cliffs broke off into the ocean occurred in the distant past, before Hawai‘i was populated. But through study and dating of these fields of slide debris still has to be done. And who can say what a volcano has in store? After all, Lo‘ihi is a very young island and might have a sudden growth spurt that could surprise us all.