1

Geology of the Hawaiian IslandsGeology of the Hawaiian IslandsClass 19Class 19

16 March 200416 March 2004

Any Questions?Any Questions?LocalLocal

Landslides, Rock fallsLandslides, Rock falls

Our Islands Are UnstableOur Islands Are UnstableFrom Shoreline to MountainsFrom Shoreline to MountainsEven the youngest parts of the volcanoes Even the youngest parts of the volcanoes are subject to landslidingare subject to landsliding

2

3

Homework #6Homework #6Due on ThursdayDue on ThursdayGo to GG 103 Home Page, Homework #6Go to GG 103 Home Page, Homework #6Read U.S. Geological Survey Report on the Read U.S. Geological Survey Report on the Sacred Falls Slide Sacred Falls Slide Write a 1Write a 1--paragraph summary of the report:paragraph summary of the report:

What was the cause of the slide?What was the cause of the slide?Will it happen again?Will it happen again?What does the USGS recommend?What does the USGS recommend?Anything you think is important/significantAnything you think is important/significantDo you think that Sacred Falls should be reopened?Do you think that Sacred Falls should be reopened?

You may either bring hard copy to the exam on Thursday You may either bring hard copy to the exam on Thursday or send the answers via email BEFORE the exam.or send the answers via email BEFORE the exam.

Manoa Falls Debris SlideManoa Falls Debris Slide

A good example of how A good example of how and why many recent and why many recent rockfallsrockfalls have have occurred on occurred on O`ahuO`ahu..

Manoa Falls Debris SlideManoa Falls Debris Slide

In January,2002, there In January,2002, there was a debris slide was a debris slide that originated at that originated at about 1400 ft and fell about 1400 ft and fell roughly 610 ft to the roughly 610 ft to the pool below. Luckily pool below. Luckily there were no known there were no known injuries or deaths.injuries or deaths.

Overview of Manoa ValleyOverview of Manoa ValleyHighly eroded with steep walls

Rock is brittle and highly weathered

Lots of clay and alteration minerals

Thick vegetation

Has active soil creep in some areas.

Average monthly rain fall for January: 11.70 in

Total rainfall for January 2002: 22.07 in (twice norm)

Average daily rainfall for January 2002: 0.71 in

4

Rocks/soil still hanging

Rainfall Rainfall Most Rain gauges on Oahu had near Most Rain gauges on Oahu had near normal or above average rainfall for normal or above average rainfall for January.January.Wilson Tunnel, Wilson Tunnel, Nu'uanuNu'uanu, and Manoa Lyon , and Manoa Lyon rain stations each received ~22rain stations each received ~22””Totals for the 3Totals for the 3--day rain storm (January 28day rain storm (January 28--30) were in the range of 2 to 8 inches. 30) were in the range of 2 to 8 inches.

Manoa rainfall for 01-2002

0

1

2

3

4

5

6

7

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31

day of month

rain

fall

in in

ches

Rainfall 1/16-1/31 Manoa

0

1

2

3

4

5

6

7

day of month

rain

in in

ches

5

ConclusionConclusionThe most likely cause of the slide was a rapid The most likely cause of the slide was a rapid

build up in weight due to water being added build up in weight due to water being added to the soil to the soil

The water also had a lubricating effect The water also had a lubricating effect

6

Questions? Questions? Thursday Thursday Exam 2Exam 2

Will cover everything since Exam 1Will cover everything since Exam 1Will be similar in form to Exam 1Will be similar in form to Exam 1(Fill in the blank and short answer)(Fill in the blank and short answer)

Thursday Thursday Exam 2Exam 2

Lectures will be stressedLectures will be stressedText for background Text for background –– illustrates and illustrates and extends conceptsextends conceptsLook at Study Questions in TextLook at Study Questions in Text

Sedimentary RocksSedimentary RocksRocks made of fragments of other rocksRocks made of fragments of other rocksRocks precipitated from a solutionRocks precipitated from a solution

Example: LimestoneExample: Limestone

Sedimentary Stages in the Rock CycleSedimentary Stages in the Rock Cycle

Sedimentary Rock ClassificationSedimentary Rock ClassificationLevel 1: Level 1: DetritalDetrital vsvs ChemicalChemicalDetritalDetrital sediments formed of material sediments formed of material eroded and transported before being eroded and transported before being depositeddepositedChemical sediments precipitated Chemical sediments precipitated directly from solutiondirectly from solution

7

Relative Relative vsvs Absolute AgeAbsolute AgeRelative: Rock “A” is older (or Relative: Rock “A” is older (or younger) than rock “B” younger) than rock “B” Absolute = knowing the age of a rock Absolute = knowing the age of a rock in yearsin yearsUsually geologists first establish Usually geologists first establish relative ages then try to get absolute relative ages then try to get absolute age datesage dates

Oldest rocksOldest rocks

Youngest rocksYoungest rocks

Principle of SuperpositionPrinciple of Superposition

Principle of CrossPrinciple of Cross--cutting cutting RelationshipsRelationships

Something (such as a dike or fault) Something (such as a dike or fault) that cuts across a layer must be that cuts across a layer must be younger than the layeryounger than the layer

Unconformity Unconformity Results from interruption of deposition Results from interruption of deposition Represents a long period of time during Represents a long period of time during which there either was no deposition, or which there either was no deposition, or earlier deposited material was eroded earlier deposited material was eroded awayaway

Summary of Geologic Events in a Summary of Geologic Events in a small areasmall area

8

Hydrologic cycleHydrologic cycle

How precipitation is apportioned How precipitation is apportioned between runoff into the ocean, between runoff into the ocean, evaporation and infiltrationevaporation and infiltration

The Hydrologic CycleNumbers are x1000 km3/yr

Rainfall In HawaiiRainfall In HawaiiMuch of the water that infiltrates Much of the water that infiltrates into the ground remains there and into the ground remains there and becomes part of the groundwater becomes part of the groundwater system.system.Averages about 190 cm (75 ") per Averages about 190 cm (75 ") per year for the island chainyear for the island chain

Rainfall In HawaiiRainfall In HawaiiNot evenly distributedNot evenly distributedSome areas receive less than 25 Some areas receive less than 25 cm (10")/yrcm (10")/yrOther areas receive more than 750 Other areas receive more than 750 cm (~300") per yearcm (~300") per yearRain Shadows Rain Shadows

Rainfall In HawaiiRainfall In HawaiiAlso not equally distributed during the year Also not equally distributed during the year We have times with little or no rain and We have times with little or no rain and times with large amounts of rain that lead to times with large amounts of rain that lead to flooding.flooding.A problem in Hawaii: The areas into which A problem in Hawaii: The areas into which water drains (drainage basins) are very water drains (drainage basins) are very small (Compare to California)small (Compare to California)

Base LevelBase LevelGenerally sea levelGenerally sea levelBut, can be changed artificiallyBut, can be changed artificiallyIf its base level is changed, a If its base level is changed, a stream will either flow faster (and stream will either flow faster (and erode more) or slower (and erode more) or slower (and probably deposit some of its load)probably deposit some of its load)

Ground waterGround water

Water that occupies the voids in rocks Water that occupies the voids in rocks below the soil layerbelow the soil layerVery Important ResourceVery Important Resource

9

Water Problems in HawaiiWater Problems in HawaiiDroughtsDroughtsNot much ability to store rain waterNot much ability to store rain waterMost rain water runs off out into the Most rain water runs off out into the oceanoceanAs development increases, the As development increases, the possibility of water shortages increasespossibility of water shortages increases

Water Problems in HawaiiWater Problems in HawaiiHalf of the water we use comes from Half of the water we use comes from groundwatergroundwater> 90% of domestic water comes from > 90% of domestic water comes from groundwatergroundwaterWe cannot really control replenishment We cannot really control replenishment of groundwaterof groundwater

Porosity and PermeabilityPorosity and Permeability

Important properties of rocks that Important properties of rocks that affect groundwater recharge affect groundwater recharge Porosity = percent of pore space in Porosity = percent of pore space in a given rock or soil volumea given rock or soil volume

Porosity and PermeabilityPorosity and Permeability

Permeability = measure of how Permeability = measure of how easily water can move through a easily water can move through a rockrock

Water Table is a surface that isfree to move up and down

10

Groundwater flows from high elevations to low elevations

AquiferAquiferA rock that has sufficient porosity and A rock that has sufficient porosity and permeability to readily yield groundwater permeability to readily yield groundwater to wellsto wellsVolcanic rocks among best on EarthVolcanic rocks among best on EarthConfined and UnconfinedConfined and Unconfined

Ghyben-Herzberg Lens

Potential Groundwater Potential Groundwater ProblemsProblems

Depletion of groundwater supplies Depletion of groundwater supplies Deterioration of groundwater qualitDeterioration of groundwater qualityy

Sustainable YieldSustainable YieldAmount of groundwater that can be Amount of groundwater that can be removed from an aquifer without removed from an aquifer without degrading (depleting) itdegrading (depleting) it

Water Problems in HawaiiWater Problems in HawaiiDroughtsDroughtsNot much ability to store rain waterNot much ability to store rain waterMost rain water runs off out into the Most rain water runs off out into the oceanoceanAs development increases, the As development increases, the possibility of water shortages increasespossibility of water shortages increases

WeatheringWeathering

Any rock at or near the earth's surface is Any rock at or near the earth's surface is constantly being attacked by wind, rain, constantly being attacked by wind, rain, chemicals, etc.chemicals, etc.This process is called weatheringThis process is called weathering

11

Two major categories of Two major categories of weatheringweathering

MechanicalMechanicalWhen rock is broken down into small pieces When rock is broken down into small pieces without any accompanying changes in without any accompanying changes in chemical composition chemical composition

ChemicalChemicalInvolves the change of a rock's chemical Involves the change of a rock's chemical composition.composition.

Mechanical weatheringMechanical weatheringGoes on everywhereGoes on everywhereIn Hawaii it is often not noticed because the In Hawaii it is often not noticed because the effects of chemical weathering are so effects of chemical weathering are so severesevere

Large rocks broken up into smaller pieces by mechanical weathering

By breaking up the rock into many pieces, By breaking up the rock into many pieces, there is more surface area available for there is more surface area available for attack by chemical weathering agentsattack by chemical weathering agents

Chemical weathering Chemical weathering

Very important in tropical climatesVery important in tropical climatesMost important elements are: Most important elements are:

oxygen from the airoxygen from the airwater from rainfallwater from rainfallcarbon dioxide generated by animal carbon dioxide generated by animal respirationrespiration

Most important chemical Most important chemical reactionreaction

Carbon dioxide combines with water to Carbon dioxide combines with water to form carbonic acid:form carbonic acid:

HH22O + COO + CO22 ⇔⇔ HH22COCO33

Carbonic acid then combines with Carbonic acid then combines with calcium to form calcium bicarbonate: calcium to form calcium bicarbonate: CaCOCaCO33 + H+ H22COCO33 ⇔⇔ Ca(HCOCa(HCO33) ) 22

Insoluble compoundsInsoluble compoundsLeft behind during chemical weatheringLeft behind during chemical weatheringMinerals disintegrate due to chemical Minerals disintegrate due to chemical weatheringweatheringSome elements combine with others to form Some elements combine with others to form new compounds that dissolve in the new compounds that dissolve in the groundwater and are carried awaygroundwater and are carried awayOther elements left behind to combine with Other elements left behind to combine with other elements and make new mineralsother elements and make new minerals

Clay mineralsClay mineralsMost important "residue" mineralsMost important "residue" mineralsSilicate minerals that contain variable Silicate minerals that contain variable amounts of water, aluminum, amounts of water, aluminum, potassium, sodium, etc. potassium, sodium, etc. Often form a large part of a soilOften form a large part of a soilControl the stability of soilsControl the stability of soils

SoilSoilUltimate result of chemical weatheringUltimate result of chemical weatheringSurficial material that has been sufficiently Surficial material that has been sufficiently weathered so that it is capable of supporting weathered so that it is capable of supporting plant lifeplant lifeEngineers: Soil = surficial material that can Engineers: Soil = surficial material that can be removed without blastingbe removed without blasting

12

Soils: 3 major zones• A horizon

(may include an upper “O” horizon)

• B horizon• C horizon

Important Clay mineralsImportant Clay minerals

KaoliniteKaolinite = most common type of clay in = most common type of clay in Hawai`iHawai`i

Reasonably stable Reasonably stable MontmorilloniteMontmorillonite is also very commonis also very common

Very susceptible to incorporating waterVery susceptible to incorporating waterThe clay then swells The clay then swells

Soil Problems at U.H. Business SchoolNovember, 1979

Mass wastingMass wastingTransportation of large masses of Transportation of large masses of rockrockDownslopeDownslope movement of rock and movement of rock and soil debris under the influence of soil debris under the influence of gravitygravityVery important kind of erosion Very important kind of erosion

Mass wastingMass wastingGravity is the driving force of all Gravity is the driving force of all

mass wastingmass wasting

Angle of ReposeAngle of ReposeSteepest angle at which fragments will Steepest angle at which fragments will stand without further sliding or rolling stand without further sliding or rolling down hilldown hillControlled by:Controlled by:

coarseness and size of fragmentscoarseness and size of fragmentsuniformity of size of the fragmentsuniformity of size of the fragments

The larger and more uniform the size of The larger and more uniform the size of the fragments, the steeper the angle of the fragments, the steeper the angle of reposerepose

Talus

LandslidesLandslidesOccur when a large piece of rock and/or Occur when a large piece of rock and/or soil breaks off and slides down hillsoil breaks off and slides down hillOften initiated by earthquakes and by very Often initiated by earthquakes and by very heavy rainstorms heavy rainstorms

Spoon-shapedsliding surface

Steep Headwall

13

LandslidesLandslidesTendency to slide increases with Tendency to slide increases with increasing surface slope increasing surface slope Addition of water promotes sliding by Addition of water promotes sliding by adding weight and by reducing cohesionadding weight and by reducing cohesionFriction along the slide surface controls Friction along the slide surface controls the speed of the the speed of the downslopedownslope movementmovement

Debris flowsDebris flowsOccur when the rock/soil mass loses Occur when the rock/soil mass loses coherency and lots of water is involvedcoherency and lots of water is involvedDebris becomes mixed up completely and Debris becomes mixed up completely and flows as liquid mudflows as liquid mudOften carry large Often carry large clastsclastsCan be very destructiveCan be very destructiveMore destructive in explosive volcanic More destructive in explosive volcanic terranes where ash blankets the slopes terranes where ash blankets the slopes and then becomes unstableand then becomes unstable

Soil CreepSoil Creep

Mass movement that moves very Mass movement that moves very slowlyslowlyWeak soils on steep slopes move Weak soils on steep slopes move slowly down hillslowly down hill

LandslidesLandslidesCertain areas are more prone than Certain areas are more prone than othersothersUsually because of local geological Usually because of local geological factorsfactors

Reducing vegetation that was Reducing vegetation that was stabilizing the soilstabilizing the soilOver watering (decrease friction)Over watering (decrease friction)

LargeLarge--scale slumping and slidingscale slumping and slidingHas affected all of the islandsHas affected all of the islandsConfirming evidence has been Confirming evidence has been discovered in the past 10 years discovered in the past 10 years Major landslides have removed very Major landslides have removed very large pieces of the volcanoeslarge pieces of the volcanoes

Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Hawaiian Ridge

Rotational slumps (nonRotational slumps (non--disintegrative) disintegrative) Debris avalanches (disintegrative)Debris avalanches (disintegrative)

Landslides adjacent to the Landslides adjacent to the Hawaiian RidgeHawaiian Ridge

Slumps occur during the major shield Slumps occur during the major shield building stagebuilding stageOnce volcanism stops, the islands are Once volcanism stops, the islands are probably stableprobably stable

Landslides adjacent to the Landslides adjacent to the Hawaiian Ridge Caused by:Hawaiian Ridge Caused by:

Volcanic activityVolcanic activityEarthquakesEarthquakes

Shake the ground and cause failureShake the ground and cause failure

14

Manoa Falls Debris SlideManoa Falls Debris Slide

A good example of how A good example of how and why many recent and why many recent rockfallsrockfalls have have occurred on occurred on O`ahuO`ahu..

ManoaManoa LandslideLandslide Questions?Questions?