Mt Ruapehu Eruption Alert

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Will one or both of New Zealand islands break up and sink in the south-western Pacific Ocean?

Update [June 30, 2008]: Ruapehu crater lake temperatures remain high

Increased risk of eruptions on Mt Ruapehu

Scientists are alarmed by an increased risk of eruptions on Mt Ruapehu. Climbers are warned about the increased gas concentrations near the Ruapehu’s crater lake that will affect some people.

In a moderate-sized eruption last year, William Pike, a geography teacher, lost part of his leg after a lahar partially buried him under tons of debris.

The crater lake temperature normally rises and drops in regular cycles. However, since the last eruption, the temperatures have remained above the of 34 – 38 °C range, a Conservation Department scientist said.

“Since September there’s been a long period of heating in the volcano, which is unusual. Normally the crater lake temperature goes up and down every nine to 15 months.

“But it has been hovering around 34-38 degrees when it normally should be lower than this.

“Basically, the temperature has stayed hot for longer this time.

“There’s no clear pattern – before the last two eruptions it was at the bottom of the cycle.”

Predicting how close the mountain was to erupting involves monitoring numerous factors, especially the crater lake temperature, the scientist said.

“It’s a combination of gas, lake temperature and magma temperature… We are issuing a warning that people should be alert if they go into the summit hazard zone.” (Source)

A train passes over a bridge over the Whangaehu River at the scene of the historic Tangiwai Rail incident after a mud flow from the crater lake of Mount Ruapehu, in the central North Island, New Zealand, Sunday, March 18, 2007. A potentially lethal mix of mud, acidic water and rocks tore down the slope of New Zealand’s Mount Ruapehu on Sunday, emergency officials said, but there was no immediate threat to life. Credit: AP Photo/NZPA, Stephen Barker (Source and Caption: Live Science) Image may be subject to copyright. See Fair Use Notice!

What’s a Lahar?

A lahar is a type of mudflow composed of pyroclastic material and water that flows down from a volcano, typically along a river valley. The term ‘lahar’ originated in the Javanese language of Indonesia.

Lahars have the consistency of concrete: fluid when moving, then solid when stopped. Lahars can be huge: the Osceola lahar produced 5,600 years ago by Mount Rainier in Washington produced a wall of mud 140 metres (460 ft) deep in the White River canyon and extends over an area of over 330 square kilometres (130 sq mi) for a total volume of 2.3 cubic kilometers (0.55 cubic miles).

Lahars can be extremely dangerous, because of their energy and speed. Large lahars can flow several dozen meters per second and can flow for many kilometres, causing catastrophic destruction in their path. The lahars from the Nevado del Ruiz eruption in Colombia in 1985 caused the Armero tragedy, which killed an estimated 23,000 when the city of Armero was buried under 5 metres (16 ft) of mud and debris. The 1953 Tangiwai incident in New Zealand was caused by a lahar. (Source)

Photo Credit: N. Banks on December 18, 1985 (USGS)

The only remaining buildings in Armero, Colombia, 72 km dowstream from Nevado del Ruiz volcano, destroyed and partially buried by lahars on November 13, 1985. Lahars reached Armero about 2.5 hours after an explosive eruption sent hot pyroclastic flows across the volcano’s broad ice- and snow-covered summit area. Although flow depths in Armero ranged only from 2 to 5 m, three quarters of its 28,700 inhabitants perished. (Caption: USGS)

Plate tectonics

Plate tectonics is a theory of geology that explains the observed evidence for large scale movements of the Earth’s lithosphere. The theory encompassed and superseded the older theory of continental drift from the first half of the 20th century and the concept of seafloor spreading developed during the 1960s. (Source)

The tectonic plates of the world (as of second half of the 20th century). (USGS)

Convergent boundary

In plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another and collide. (Source)

Will a magnitude 9.8 (M_W) earthquake centered at 42° 00′ 59″ South, 175° 05′ 07″ East herald the end of New Zealand Islands?

New Zealand’s Alpine Fault. Image may be subject to copyright. SEE Fair Use Notice!

Topography of New Zealand (NASA Visible Earth)

Credit: NASA Image courtesy JPL/National Geospatial-Intelligence Agency

New Zealand straddles the juncture of the Australian and Pacific tectonic plates. The Australian Plate is on the west side of the boundary, while the Pacific Plate is on the eastern side. The two plates converge in a scissor-like pattern. In the northern part of the boundary, the Australian plate overrides the Pacific plate, and in the southern part of the plate boundary, the Pacific plate overrides the Australian plate. New Zealand sits in the area around the cross point of this tectonic scissor pattern. (For help visualizing the process, take two index cards and arrange them side by side. On the left-hand card make a cut from the middle of the right edge toward the center. Lift up the top “flap” created by the cut and slide the right-hand card into the cut. Let go of the flap. The left-hand card is the Australian Plate; the right-hand card is the Pacific Plate.)

The collision of the two plates has built two major islands that together exhibit active volcanoes and fault systems, and these geologic features are very evident in the topographic pattern. The image above shows a topographic map of the North and South Islands of New Zealand made from radar data collected by the Space Shuttle Endeavor. Elevation is color-coded, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations. Shading reveals the direction of slopes. Northwest slopes appear bright, and southeast slopes appear dark.

The North Island lies at the southern end of the west-over-east (Australian over Pacific) plate convergence. Here, the Pacific plate dives under the North Island, and the immense heat and pressure created by this subduction process melts the deep rock. The melted rock (magma) rises to the surface through the North Island’s volcanoes and other geothermal features. Most notable are Mount Egmont on the west coast, and Mounts Ruapehu, Ngauruhoe, and Tongariro, clustered just south of the island’s center. The Rotorua geothermal field is northeast of that cluster of volcanoes, and the field appears as a scattering of bumps created by smaller volcanic eruptions.

The South Island straddles the “cross point” of the subduction scissor pattern. To the north of the cross point, the Pacific Plate goes under the Australian Plate; to the south of the cross point, it goes over top. This area around this cross point is not in either subduction zone, which explains why it lacks the volcanic activity of the North Island.

Instead, South Island features a fault system that connects the northern subduction zone to the southern one, which occurs south of South Island. The Alpine fault is the major strand of this fault system along most of the length of the island, near and generally paralleling the west coast. Its impact upon the topography is unmistakable, forming an extremely sharp and straight northwest boundary to New Zealand’s tallest mountains, the Southern Alps. Along the Alpine Fault, the plates are sliding past each other (moving horizontally) somewhere between 35-40 millimeters per year. Vertical differences between the two plates increase at a rate of about 7 millimeters per year, which is consistent with the ongoing uplift of the Southern Alps.

Elevation data used in this image were acquired by the Shuttle Radar Topography Mission aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth’s surface. To collect the 3-D data, engineers added a 60-meter (approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Geospatial-Intelligence Agency (NGA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., for NASA’s Earth Science Enterprise, Washington, D.C.  Caption: Visible Earth.

Related Links:

• Plate Tectonics, the Cause of Earthquakes
• None Shall Sleep!
• Earthquake Topics — Plate tectonics
• Plate tectonics and people
• Evolving Earth: Plate Tectonics
• Plate tectonics