Unit 3: THE LIVING MACHINE

The concept of a hot spot envisions a small source of heat fixed deep in the Earth, below the lithospheric plates (Figure 3-7). Molten rock from the heat source rises rapidly, melting its way through the overlying lithospheric plate and emerging on the surface to form a volcano. But because the plate is moving, the volcano is soon carried away from the point over the heat source, and becomes dormant. The hot spot burns its way through the lithosphere directly above it and begins to construct a new volcano. The result is an ever-lengthening line of volcanoes whose abrupt beginning at an active vent marks the location of the hot spot itself.

The Hawaiian island, other volcanic centers, and earthquake motions, such as those observed during the 1964 Alaskan Good Friday earthquake, show the correctness of the dynamic nature of Hutton's and Lyell's paradigm of a vital earth. The Neptunist pronouncement of "mountains eroding and tumbling down to the sea" is turned on it's head in the images below. Here volcanic lava flows do meet the sea, however, they are building new regions and enlarged portions of the Hawaiian Island as they enter the Pacific ocean and cool.

HM 3-25 (A-C): Earthquakes and Seismicity.

A) Earthquakes associated with the Hawaiian hotspot (National Earthquake Information Center)

B) Hotspot tracks form distinctive arcuate patterns in the Pacific basin. Their similiarity in direction strongly suggests that the hotspots themselves have remained relatively fixed with respect to the overlying lithosphere.

C) At a global scale, these hotspot tracks are some of the most noticable features on the surface of Planet Earth. Here earthquake epicenters < 100 km are shown in light blue, deeper earthquakes by yellow, volcanic centers are purple markers.

As an analogy, consider the action of a sewing machine. The needle can move up and down, but stays in one spot, repeatedly piercing the cloth which moves under the needle. The result is a line of stitches starting at the needle and proceeding away from it in the direction that the cloth is moving.

In the same way, the Hawaiian Islands are created by the fixed hot spot, and the moving Pacific plate carries the finished products away to the northwest. The line of volcanic islands defines the direction toward which the plate moves.

Figure 3-3 shows the locations of some two dozen hot spots. Many of them, such as Hawaii, are located far from plate boundaries, and others, such as Iceland and the Azores, are located on spreading ridges.

Oceanic hot spot volcanoes erupt basaltic lava that is rich in the mantle mineral olivine. Continental hot spots must melt their way through many kilometers of granitic continental crust, and so the volcanoes associated with them range from basaltic to rhyolitic in composition. Rhyolite has the same composition as granite, but is fine-grained and results from rapid cooling of granitic magma once it is erupted on the surface as lava.

The origin of hot spots is still uncertain. While Figure 3-7 shows a hot spot source extending down into the asthenosphere, that only represents how far down they have been traced to date. That they may have their origin very deep in the mantle is suggested by studies of the motions of hot spots.

Once the motions of all the major plates were worked out for the past few million years, it was found that the volcanic traces of all the hot spots could be correctly predicted by a model in which the hot spots are fixed in position in relation to one another. Recent research indicates that over long periods of geological time, the hot spots do move, but this motion is much slower than that of the lithospheric plates.

This is unlikely to be the case if their source is in the highly mobile asthenosphere. The deeper mantle is more rigid than the asthenosphere, and it has been suggested that the hot spots have their source in this less mobile region.

If so, the nature of the hot spots is truly remarkable. A source of heat, perhaps thousands of kilometers deep within the Earth, produces superhot material that gathers into a thin rising column. Almost like a laser beam it burns its way upward to the surface to produce volcanic activity like that of Hawaii and Yellowstone.

Now at last we can answer a question posed earlier: Why are there continents and ocean basins on Earth? We got as far as realizing that continents exist where the crust is thick and is composed of low density rocks such as granite. Ocean basins exist where the crust is thin and basaltic in composition. The process of isostasy then determines the relative elevations of the continents and ocean floors.

Plate tectonic theory allows us to go another step toward an explanation. Basaltic ocean crust is created at spreading ridges, and granitic and andesitic continental crust is created beneath the volcanoes associated with subduction zones. Volcanic island arcs are bits of newly created continental crust that eventually coalesce into small continents, like the Japanese Islands, or are plastered onto the edges of larger continents.

Oceanic crust, on the other hand, is very ephemeral. Created at the oceanic ridges and destroyed at the subduction zones, the floor of the ocean basins can never reach a truly ancient age. The age of the oldest ocean floor does not exceed 200 million years. This can be compared with ages for continental rocks that range back to 3,800 million years. All the ocean floor that exists today has been created since Pangea began to break up.

We need to answer one final question: Why do spreading ridges produce only basaltic crust, and why do subduction zone processes generate andesitic and granitic crust?

The process begins at the oceanic ridges, where hot mantle material wells up beneath the ridge crest and partially melts. The mantle is composed of a rich mix of many different minerals. Dominant are the dense silicate minerals olivine, garnet, and pyroxene. But also mixed in are smaller proportions of the lighter silicates that make up granite and basalt.

The partial melting beneath the ridge results in a kind of distillation or fractionation process that selectively incorporates the lighter minerals of the mantle into the oceanic crust. The process may be compard with the distillation of fermented grain, in which the more volatile alcohol is concentrated in the finished product. At the oceanic ridges, the end product is a basaltic rock, dark in color and moderately dense, though far less dense than the parent mantle rock. This becomes the thin crust of the ocean floor and is carried away rapidly by the plate tectonic conveyor belt.

At a subduction zone, the basaltic ocean crust is carried down below the trench and cooked by the Earth's internal heat along with frictional heat produced where the plates rub together. The subducted crust has been exposed to the oceanic environment for many millions of years, during which time it has been altered by chemical reactions with seawater and has accumulated a thick covering of sediment. Some of this sediment is scraped off the oceanic crust when it is subducted, but recent evidence indicates that some of it is also subducted. In addition, large quantities of water contained in the crust are also subducted.

Partial remelting of the altered oceanic crust along with subducted ocean floor sediments results in a second stage of fractionation, further concentrating the lighter minerals and producing molten rock of andesitic and granitic composition. Eventually this material is added to the continental crust by the andesitic volcanoes.

The question of whether the total volume of all the continents is now increasing with time is still a subject of debate. While new continental material is added by subduction zone volcanics, continental material is also removed by erosion, deposited on the ocean floor, and eventually subducted once again. We cannot as yet determine which, if either, of these two processes is dominant at the present time.

Turn again to Figure 3-3. Because new plate is created at the ridges and old plate is destroyed at subduction zones, plates naturally move from the ridges toward the trenches.

Consider the Pacific Plate. It is gaining new crust at the East Pacific Rise on its southeastern edge and it is being destroyed in the trenches at the north and west sides of the Pacific Ocean. As seen from its neighboring plates, its motion is from the southeast toward the northwest.

HM 3-26 (A-D): Earthquakes and Seismicity.

A) Seismicity of the Pacific Basin, Pacific plate motion is towards the northwest (upper left).

B) Pacific plate subduction is shown by the location of earthquake epicenters (> 50 km-yellow dots) and volcanic centers (purple symbols).

C) Three dimensional view of the portion of Pacific plate subduction zone near the volcanic arcs which make up Japan and the Kuril Islands. Note the deep trench along which the Pacific plate subducts beneath the nearby overriding plates.

D) Subduction zones of the western Pacific. Shallow earthquakes 0-50 km are light blue dots, earthquake epicenters between 50 and 100 km are white dots, deeper earthquakes are yellow. Active volcanic centers are shown are purples crosses.

The Nazca Plate moves in an easterly direction from the East Pacific Rise toward the Peru-Chile Trench.

HM 3-27 (A-C): Earthquakes and Seismicity.

A) Seismicity of the eastern Pacific region.

B) Seismicity of South America (National Earthquake Information Center)

C) A more detailed view of seismic activity along the southwestern coast region of South America.

The motion of North America seems more complex, but follows the same general rules. As seen from Europe, the North American Plate moves westward, away from the Mid-Atlantic Ridge. At the San Andreas Fault, the North American Plate encounters the north-westerly moving Pacific Plate. Because both plates are moving to the west, the result is the slipping motion of a transform fault rather than subduction.

HM 3-28 (A-I): Earthquakes and Seismicity.

A) Arctic Ocean earthquake seismicity (National Earthquake Information Center)

B) North Atlantic earthquake activity (National Earthquake Information Center)

C) South Atlantic earthquake activity (National Earthquake Information Center)

D) Three dimensional view of the central Atlantic Rift. Earthquake epicenters (>50 km depth) are shown as yellow dots. Note the distinct continental rises that are a result of isostasy. North is to left, south to right side of this oblique perspective image.

E) Western United States seismicity (National Earthquake Information Center)

F) Seismicity of the United States. The earthquakes on the left portion of this figure are related to the active plate boundaries of the North America plate. Earthquakes in the central and right hand portion are "within plate" events. The most significant seismic hazard for the central and eastern United States is the New Madrid fault region outlines by seismicity along the western borders of Kentucky and Tennessee.

H) Seismicity and volcanic activity. Volcanic centers are shown by white crosses, 100 km buffer zones are drawn around the volcanic centers. earthquake epicenters (less than 50 km in depth) are shown as dark red dots.

I) Central America and the Gulf of Mexico. The Caribbean plate, the deep basin-region north of South America, is clearly seen in this region. Oblique perspective image with north at top.

These motions can become very complex, since the direction of motion of a plate, as it appears to you, depends on where you happen to be standing. It is rather like the case of a ferry slowly moving away from its dock. To someone on the dock, the ferry is moving out to sea. But to someone on the ferry, it can appear as though the dock is moving away from the ferry. In the same way, someone standing on South America sees Africa moving away to the east, while an observer on Africa sees South America moving away to the west.

As a final case, consider the Indo-Australian Plate. It is moving to the north, away from the spreading ridge in the Indian Ocean. On its north-central boundary, there is indeed a subduction zone marked by the Java Trench. But its northwestern edge falls along the northern boundary of India -- the Himalayas.

HM 3-29 (A-H)

A) Seismicity of Australia region (National Earthquake Information Center) showing the Indonesian volcanic arc. The motion of the Indian-Australian plate is towards the north. Subduction zones marking the western edge of the Pacific plate are easily seen. Note the extensive subduction zone marking the western edge of the Philippine plate.

B) Seismicity of the Indian Ocean, clearly showing the rifting of the African plate, and motion between the Arabian-African, African-Indian/Australian, Africa-Antarctica, and Indian/Australian-Antarctica plate pairs. National Earthquake Information Center.

C) A view of seismicity of the South Pole. Note that spreading between the Antarctic- Indian/Australian plates results in the northward motion of the Indian/Australian plate. Seismic events associated with other spreading and subduction zones are clearly seen as well as events associated with the rifting of the African plate (National Earthquake Information Center).

D) Earthquake activity of central Asia (National Earthquake Information Center).

E) Three dimensional view of Indian plate collision with Eurasia, (north is along the top edge of the image). This collision has produced the highest present-day mountain system on the surface of Planet Earth.

F) Oblique perspective view of the collision zone between the Arabian and Indian plates with the southern edge of the Eurasian plate (earthquake epicenters > 50 km are marked with small yellow dots).

G) The Mount Everest region as seen from space (NASA image). Mt. Everest is in the central area, glaciers and moraines are clearly seen (refer to Unit 8, The climate puzzle: Climates of the Earth, for many additional information regarding glaciers and moraines).

H) A portion of Tibet as seen from the space shuttle, note the lack of vegetation (NASA image). It has been suggested that the weathering of rock in this large uplifted and mostly unvegetated area led to a decrease in the amount of atmospheric carbon dioxide gas (an important greenhouse gas, see Unit 8). This decrease in atmospheric carbon dioxide may have contributed to global cooling and the present cooler climate of Planet Earth.

Here we see two continents in the act of colliding. India, in its long northward trek from its original home near Madagascar, has rammed into the underbelly of Asia, and the result is the highest mountain range on Earth. Much the same is happening in the Alps, where the northern motion of Africa is forcing Italy against the European continent.

HM 3-30 (A-D): Earthquakes and Seismicity.

A) Seismicity of Europe (National Earthquake Information Center)

B) Seismicity along the southern boundary of the Eurasian Plate. The approximate boundary between the Eurasian and North America plate is shown by the yellow line near longitude 120E.

C) Earthquakes associated with the spreading between the African and Arabian plates are seen in the Red sea and northwestern Indian ocean. Earthquakes associated with the collision of the northern edges of the African and Indian plates with the Eurasian plate are expressed as a east-west zone of seismicity across the upper portion of this figure.

D) Shallow earthquakes (light blue dots) and active volcanic centers (purple crosses). Note the Mid-Atlantic and African spreading systems, and seismicity resulting from the collision of the African and Eurasian plates in the Mediterranean region. The seismic activity in southern Norway (at the top of the image) is associated with lithospheric rebound. During glaciation (about 12,000 years ago), this lithospheric region was slightly depressed by glacial ice loading. Since the melting of this mass, lift caused by isostasy is occurring. Associated with this lift is limited and small magnitude seismicity. Similar processes result in occasional small earthquakes in eastern Canada.

As though they were two automobiles in a collision, the continents display the equivalent of crumpled fenders and twisted frames in the tortured and distorted strata of rock found in these mountain-building collision zones (see Figure 3-15).

HM 3-31 (A-B)

A) Oblique perspective view of the Mediterranean collision zone showing topography and seismicity North is located along the top of the image.

B) The collision zone between the African plate and the southern edge of the Eurasia plate in the Gibraltar region. This narrow outlet for the Mediterranean sea has been closed several times in the relatively recent past (see Unit 6 for additional details regarding the drying of the Mediterranean).

Geologists have found evidence for just such a history in the Himalayas and Alps, which are still active today, as well as in the long-dormant Urals of Russia and the Appalachians of the eastern United States.

Africa is moving to the north, driving the north of Italy into the heart of Europe to form the young Alps, just as India is forcing its way into Asia. The Urals would appear to mark an ancient collision between Europe and Asia. But what of the Appalachians?

The bend of the mountain ridges as they pass through Pennsylvania seems to hint that the bulk of the colliding mass came from the southeast. Could it have been Africa that smashed into the east coast of North America at the end of the Paleozoic, some 300 million years ago? If so, the existence of the Appalachians testifies to an event that was part of the assembly of Pangea.

In all of this we sense a mobility through the ages that seems to transcend anything that Wegener envisioned. Now that we know how the plates are moving today, is it possible to reconstruct the motions of the plates throughout the history of Planet Earth? At least a partial answer to this question comes from an unexpected source: the study of the Earth's magnetic field.

Magnetic compasses have been in use as navigational aids for at least 700 years. A magnetized needle is suspended so that it can rotate freely about a vertical axis. When it comes to rest, we find that it points approximately toward the North Magnetic Pole.

When certain kinds of volcanic rocks cool and crystallize from the molten state, they "freeze in" a memory of the direction of the magnetic field in which they cooled. In a sense the magnetic atoms in the rock act rather like fossilized compasses that can tell us which way was north at the time the rock formed.

As it turns out, rock magnetism can tell us even more about the ancient magnetic field than an actual compass could. Figure 3-16 shows the shape of the present day Earth's magnetic field.

Lines of force of the magnetic field emerge from the southern hemisphere, loop through space, and reenter the Earth in the northern hemisphere. Notice that the lines of force point down into the ground in the northern hemisphere and up out of the ground in the southern hemisphere.

Magnetic lines of force are a convenient way of representing the direction that a freely suspended compass needle would point at any location within a magnetic field. They do not really exist as lines, and the magnetic field itself is invisible. A magnetic field is capable of exerting a force on a magnetized needle, turning it so that it points in a preferred direction. We say that the magnetic field points in this direction.

At the South Magnetic Pole the magnetic field points straight up out of the ground; at the magnetic equator it is horizontal (parallel to the ground surface), and at the North Magnetic Pole it points straight down into the ground. At intermediate magnetic latitudes the angle that the magnetic field makes with the Earth's surface varies smoothly as shown in the graph in Figure 3-18. In other words, if we know the angle that the magnetic field makes with the horizontal and whether it is pointing up or down, then we can determine our magnetic latitude.

For example, if you were to find yourself imprisoned in a room with no windows, you might learn your approximate latitude by measuring the direction of the magnetic field in the room. If, say, you found that the magnetic field pointed down into the ground making an angle of 40° (down) on the vertical axis of the graph in Figure 3-18, draw a horizontal line from it to the curve, then drop straight down to the horizontal axis to find that you are somewhere around 23° North latitude. On the other hand, if you were to find that the magnetic field pointed up out of the ground at an angle of 60°, then you could conclude that you must be somewhere around 41° South latitude.

There is a problem here because at the present time the magnetic axis is tilted some 11 degrees from the geographic axis of the Earth. What we would really like to know is the geographic, not the magnetic, latitude.

Studies of rocks which are no more than a few million years old show that at any given time the magnetic and geographic poles may differ by as much as 15 degrees, but on the average, the magnetic poles are in fact centered on the geographic poles. The magnetic pole moves with time, shifting about the geographic pole in a more-or-less random manner. Over a period of a few thousand years, however, its average position is found to coincide fairly closely to that of the geographic pole. This has apparently been the case throughout most of geologic time. In paleomagnetic investigations, large numbers of samples spanning a time interval of more than a few thousand years must be examined in order to ensure that the ancient geographic latitude has been determined.

An ordinary compass cannot give us enough information to do this, but frozen in place in a cooled volcanic rock, the magnetic atoms can. Using sensitive instruments called magnetometers, geophysicists coax from cooperative rocks information about the direction of the recorded magnetic field, enabling them to determine which way was north when the rock crystallized; and at what latitude did it form. Fortunately, some sedimentary rocks are also capable of recording the direction of the magnetic field when they form.

Here is a tool of tremendous utility. The study of paleomagnetism (the word literally means "ancient magnetism") provides us with much of the information we need to retrace the wanderings of the continents during the past several hundred million years.

Nonetheless, paleomagnetism does not give us all that we would wish. For a given continent at a given age, we can determine the ancient direction of north (that is, the orientation of the continent) and the ancient latitude. It tells us nothing about the ancient longitude.

But that is enough to tell us a great deal about the motion of the continents. Rocks of various ages in North America have been examined and yield the information shown in Figure 3-19.

We can see that in the Early Paleozoic, North America was located on the equator and was tipped far over to the right. As time went on, the continent changed its orientation rapidly in a counterclockwise direction and then shifted in latitude by moving to the north.

We can do the same thing for all the continents, but the absence of longitude control makes it hard to know just how they should be placed in relation to one another.

Yet another feature of the Earth's magnetic field comes to our assistance by providing the missing information, at least for the past 200 million years. This feature is the propensity of the Earth's field to suddenly interchange its North and South Magnetic Poles. These events are termed magnetic polarity reversals.

After a polarity reversal occurs, the magnetic field at every point on Earth points in the opposite direction to that which it had prior to the reversal. (Compare Figure 3-16 with Figure 3-17).

Polarity reversals happen very quickly, at least from a geological point of view. It may take no more than a few thousand years for the field to flip to its new opposite configuration. During the past 50 million years, polarity reversals have occurred at an average rate of a few per million years, though exactly when they occur seems to be randomly determined.

The history of polarity flips during the last five million years is shown in Figure 3-20. It was determined by collecting lava flow samples of different ages. Each sample was age dated by radioisotope methods and also was measured in a magnetometer. If the magnetization in the rock pointed north, the sample was classified as being magnetized in the normal sense. If it pointed south, the sample was classified as being magnetized in the reversed sense.

From the diagram, you can see that the magnetic field has been normal for the past 730,000 years, was reversed from 730,000 years ago until 900,000 years ago, etc. This pattern of polarity reversals has been verified by many thousands of additional samples measured since the original determination.

At first sight, the presence of polarity reversals seems to be an enormous complication in applying paleomagnetism to continental drift. In fact, the average time of polarity intervals (less than a million years) is so short compared to the time needed for significant continental motion (tens to hundreds of millions of years) that separating the two effects is usually possible.

For instance, if two rocks differ little in age but contain magnetizations that point in opposite directions, then it is clear that we are dealing with a polarity reversal and not with some sudden jump in the continent's position.

The Earth's magnetic field arises from large electric currents circulating in the liquid iron core. These currents in turn arise from convective motions of the fluid and a complex interaction between them, the electric currents, the magnetic field, and the Earth's rotation. The Earth acts like an electric generator, or dynamo, using its rotation and internal heat energy to produce electric and magnetic fields. When the polarity of the field changes, all that is needed to accomplish this is for the electric currents to reverse their direction as well. The physical motions of the Earth are not likely to be affected in this process.

HM 3-22 (A-H): FISSURE ERUPTION!
A) Curtain of fire along the northeast rift zone of Mauna Loa Volcano; the view is to the south. The height of the fountain is approximately 25 m. Geologists at left. Hawaii Volcanoes National Park. Hawaii County, Hawaii. March 25, 1984. (Images and captions from USGS).	B) Mauna Ulu phase 2; fountain and cascade into Aloi. Hawaii Volcanoes National Park. Kilauea east rift. Hawaii County, Hawaii. October 20, 1969.

C) Oblique aerial view of curtain of fire at fissure on Kilauea's east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. January 3, 1983.	D) Arching lava fountain. Kilauea east rift eruption. Hawaii Volcanoes National Park. Hawaii County, Hawaii. February 25, 1983.

E) Mauna Ulu. A'a flows at base of Holei Pali; geologist in foreground for scale. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. February 28, 1971.	F) View of surface pattern at east end of Mauna Ulu summit lake, just west of septum breach. Kilauea east rift, Hawaii Volcanoes National Park. Hawaii County, Hawaii. August 27, 1972.

G) Mauna Loa Volcano. A'a flow front. Fast moving front of flow, characterized by low toe (1-3 m.) and explosed fluid core. Flow front at 1800 meter elevation. Hawaii County, Hawaii. April 5, 1984.	H) Squeeze-out from a'a flow front west of Alae. Mauna Ulu. Kilauea east rift: Hawaii Volcanoes National Park. Hawaii County, Hawaii. April 14, 1972.

HM 3-23 (A-J): The low viscosity of the magma allows it (while very hot) to flow almost like a firely water. Downslope from the erupting volcanic center volcanic tubes where they break to the surface combined with the considerable momentum of the dense magma can result in spectacular fountains of magma
A) Arching lava fountains from vents on east flank of Mauna Ulu. Kilauea east rift. Hawaii County, Hawaii. October 15, 1970. (Images and captions from USGS).	B) Spatter cone formed during the April 30, 1982 eruption in Kilauea caldera. The approximate diameter of the vent is 2 m. Photo catches spatter in mid-air. Hawaii Volcanoes National Park. Hawaii County, Hawaii.

C) Mauna Ulu fountain. Hawaii Volcanoes National Park. Hawaii County, Hawaii. September 6, 1969.	D) Mauna Ulu dome fountain (artesian type); phase 10, 50-75 m in height. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. October 11, 1969.

E) Mauna Loa Volcano. Oblique aerial view, looking west, of echelon eruptive fissures in Pohaku Hanalei area at dawn. Hawaii Volcanoes National Park. Hawaii County, Hawaii. July 6, 1975. Erupting magma, note release of gas associated with the magma during rainstorms the rain vaporizes when it strikes the hot surfaces produces instant zero visibility. Combined with the low and often featureless slope this is a significant risk to people studying the volcanic activity.	F) Oblique aerial view of fountains long echelon fissures on the northeast rift zone of Mauna Loa Volcano. Pohaka Hanalei cinder-spatter cone is at the upper left. Hawaii Volcanoes National Park. Hawaii County, Hawaii. March 25, 1984.

G) Lava tube. Here lava is flowing rapidly through an underground tube. The insulating crust allow the magma to retain most of it's heat and remain very fluid, flowing very long distances. To researchers, these tubes are a significant danger (the crust over the tube can be very thin or unstable). Lava tube P72 skylight. Mauna Ulu. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. February 7, 1973.	H) Mauna Ulu. D. W. Peterson sampling lava tube. Kilauea east rift, Hawaii Volcanoes National Park. Hawaii County, Hawaii. January 30, 1973.

J) Makaopuhi lava lake, aerial view; lava cascades at left. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. March 5, 1965.	K) Incandescent accretionary lava ball approximately 0.75 m long, Royal Gardens, Kalapana, east rift zone of Kilauea Volcano. Hawaii County, Hawaii. July 2, 1983. The lower temperature has significantly increased the viscosity of the magma and it is beginning to harden.

HM 3-24 (A-F): Hawaiian flows entering the Pacific ocean
A) Lava flow blocking highway, people provide scale. Hawaii Volcanoes National Park. Hawaii County, Hawaii. June 1989.	B) Oblique aerial view southwestward of hydraexplosion clouds over the lava front at the ocean. In the background, under the plane wing, the lava fountains and fume cloud are visible. The 1959-60 Eruption of Kilauea Volcano. Hawaii Volcanoes National Park. Hawaii County, Hawaii. January 15, 1960.

C) Mauna Ulu. Lava enters sea at bay between Kaena Point and Kealakomo. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. September 17, 1972.	D) Mauna Ulu. Lava enters sea at Kaena Point. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. September 17, 1972.

E) Mauna Ulu. Spatter from explosion of lava at shore. Kilauea east rift. Hawaii Volcanoes National Park. Hawaii County, Hawaii. April 12, 1971.	F) Mauna Ulu. Lava enters sea west of Apua Point. Kilauea east rift, Hawaii Volcanoes National Park. Hawaii County, Hawaii. April 10, 1973.