Hawaii Shelf Collapse 122005

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Hawaii Shelf Collapse 12-2005

• The following set of slides is of a recent shelf
  collapse on the Big Island of Hawaii. During the
  2005 Advanced Geology trip to Hawaii, we hiked
  out to a viewpoint that was close to where this
  collapse took place. The day we hiked out there,
  there was a minor collapse that essentially led
  to this major one. We of course hiked well
  inland of the coast.
• Current lava pictures were taken from
  http//hvo.wr.usgs.gov/kilauea/update/video
  slides 3,4, 19, 22, 27, 32, 33, 34 taken by Dan
  Brownstein
• The images are all from June 29th to Dec 3rd 2005

Slide Show by Daniel Brownstein
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We were standing several hundred feet upslope of
the circle (see next slide). Note that there are
several breakouts just beyond that. This picture
is from June 30th and we were there on the 29th.
Check out the fractures (red and blue ovals) that
were right below us in the delta. This is where
the collapse took place. Everything to the left
of that fracture (the red one) is in the ocean
now. The new cliff is 100 ft!
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What we saw from that vantage point
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The steam plume on June 29thvisible from over
40 miles away
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We were right here on June 29th!
Our approximate path
July 7 2005
Approx ¼ mile
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Close up of lava delta July 2005. Note huge
crack formed the previous day. To the left of the
crack is spatter that came out of the crack
when it formed. Lava is visible entering the
ocean at the bottom left
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Why Shelves Collapse

• Lava pours into ocean chaotically
• Layer upon uneven layer leads to a small delta
• Undercutting by ocean destabilizes delta
• Eventually the delta will collapse
• This sometimes forms a series of steps
• A drop down ledge is called a bench
• Next slide diagrams this process

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1
2
3
4
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November 1st
X
We were here
December 1st
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November 1st
December 1st
45 acres of land fell into the ocean
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Before (above)After (below)
Point A
Point B
Point A
Point B
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Where you shouldnt stand
Pictures of current flow into ocean over new cliff
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Note that after 2 dayssmall delta/cone has built
up below lava falls
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1. Note location of lava tube (now exposed in
cliff face) 2. Note gypsum/sulfur deposits that
formed along new crack near cliff facethese
commonly form along fractures above underground
lava (see next slide)
Dec 2 2005
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Puu Oocurrent site of eruptionalong Kilaueas
East Rift Zone
From herelava travels mainly underground to
ocean via lava tubes
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Lava tubes form because the surface of a lava
flow will cool first. Basalt is an excellent
insulator and keeps lava underneath new crust
relatively hot, which allows it to flow rapidly.
When lava cools, it becomes thicker (more
viscous) and slows down.
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Lava tube cavewhen lava stops flowing it can
leave behind a cave like this one. This lava
tube is part of a miles long set of tubes on
Mauna Loa
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Current pahoehoe flows. Note that within the
flow there are black specks. These are
solidified pieces of basalt, which slows down the
lava
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Pahoehoe
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When solidified, pahoehoe looks like this
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Skylight into Lava Tube Since the top portion
of the tube is relatively thin, pieces of the
tube can collapse, forming a skylight.
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Skylight into Lava TubeOctober 2005
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Psychotic Geologists
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The geologic history of Hawaii is filled with
examples of much more catastrophic island
collapses

• These collapses can create mega tsunamis with
  waves over 2000 feet tall. Shells carried from
  such waves have been found thousands of feet
  above sea level on some of the Hawaiian
  volcanoes.

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Note re-growth of delta (only 3 weeks after
collapse) Also, the shelf is showing signs of
new fracturing
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The Kohala CoastBig Island
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The Na Pali Coast (3500ft)Kauai