Graehl (2009) Sand deposition mech

SAND DEPOSITION MECHANISMS IN HOLOCENE MARSH STRATIGRAPHY FROM A

TSUNAMI PRONE LOCALITY, CRESCENT CITY, CALIFORNIA, SOUTHERN

CASCADIAN MARGIN

by

NICHOLAS ADAM GRAEHL

A Thesis

Presented to

The Faculty of Humboldt State University

In Partial Fulfillment

of the Requirements for the Degree

Bachelor of Science in Geology

May 14th, 2009

SAND DEPOISTION MECHANISMS IN HOLOCENE MARSH STRATIGRAPHY FROM A

TSUNAMI PRONE LOCALITY, CRESCENT CITY, CALIFORNIA, SOUTHERN

CASCADIAN MARGIN

By

Nicholas A. Graehl

iii

ABSTRACT

SAND DEPOSITION MECHANISMS IN HOLOCENE MARSH STRATIGRAPHY FROM A TSUNAMI PRONE LOCALITY, CRESCENT CITY, CALIFORNIA, SOUTHERN

CASCADIAN MARGIN

Nicholas A. Graehl

The objectives of the current study were to describe the stratigraphy of South Crescent Marsh

and to identify the candidate processes responsible for anomalous sand sheets in this coastal

freshwater marsh. Understanding the depositional mechanisms for the emplacement of

anomalous sands in coastal marshes will aid in the interpretation of marsh stratigraphy. To

investigate the stratigraphy at South Crescent marsh, 18 gouge cores were extracted along a

transect perpendicular to Crescent Beach that bisected the adjacent beach berm and South

Crescent Marsh. The subsurface stratigraphy was mapped approximately 200 meters east from

the western most edge of the marsh. All one-meter-long gouge cores were extracted at closely

spaced intervals to better asses the continuity of the subsurface stratigraphy and to facilitate in

layer correlations across the marsh. Four laterally continuous sand sheets were documented

within the stratigraphy of South Crescent Marsh. Because the marsh is a prime wash-over setting

located at MHHW behind a relatively small beach berm, elevated ocean levels from both

tsunamis and storms have an equal chance of inundating this area. Therefore the candidate

mechanisms responsible for the deposition of these four sand sheets are (1) near-field tsunamis

generated from the CSZ, (2) far-field tsunamis generated from within the Pacific Rim, and (3)

storm-waves caused by extreme climatic conditions. Findings from this study cannot attribute

with certainty which process caused the deposition of each of the sand sheets.

iv

DEDICATION

To my future child,

may we live life as a surprise like your birth will sure be

v

ACKNOWLEDGEMENTS

This work was supported in part by Lori Dengler of the Humboldt State Geology

Department. Her expertise, guidance, and genuine support were beneficial to the completion of

this report. A big thank you goes to Harvey Kelsey for project guidance and the technical review

of this paper. His work with paleoseismic investigations is an inspiration. Redwood National

Parks gave permission for this work in South Crescent marsh. Thanks to Chris Turner for helping

survey the study site, Bud Burke for letting me explore my thoughts about this project in Senior

Seminar, Curt Peterson for sharing his thoughts and work with me. And finally, to my wife,

Launa, who helped encourage and inspire me throughout this endeavor. This project would not

have been possible without her support, including incredibly good home-cooked food, countless

reviews, and most of all her unconditional love.

TABLE OF CONTENTS

ABSTRACT .................................................................................................................................... 3

DEDICATION ................................................................................................................................ 1

ACKNOWLEDGEMENTS ............................................................................................................ 1

INTRODUCTION .......................................................................................................................... 1

Crescent City ....................................................................................................................... 2

Setting ................................................................................................................................. 3

METHODS ..................................................................................................................................... 4

Selection of Study Site ........................................................................................................ 4

Field Study .......................................................................................................................... 4

RESULTS ....................................................................................................................................... 6

Stratigraphy ......................................................................................................................... 6

Mud ......................................................................................................................... 7

Muddy-peat ............................................................................................................. 7

Peaty-mud ............................................................................................................... 7

Peat .......................................................................................................................... 7

Sand......................................................................................................................... 7

Sand Sheets ......................................................................................................................... 8

Sand Sheet I ............................................................................................................ 8

Sand Sheet II ........................................................................................................... 8

Sand Sheet III .......................................................................................................... 9

Sand Sheet IV ......................................................................................................... 9

DISCUSSION ............................................................................................................................... 11

Sand Sheet I ...................................................................................................................... 11

Sand Sheets II and III ........................................................................................................ 11

Sand Sheet IV ................................................................................................................... 12

CONCLUSION ............................................................................................................................. 14

REFERENCES ............................................................................................................................. 15

LIST OF TABLES ........................................................................................................................ 18

Visual and Tactile Estimation of Lithology ...................................................................... 19

Sand Sheet Attributes from South Crescent Marsh .......................................................... 20

Individual Core Attributes ................................................................................................ 21

LIST OF FIGURES ...................................................................................................................... 22

Tectonic Overview and Northern California Tsunami Sites ............................................. 23

Magoon’s 1964 Far-Field Tsunami Inundation Map ........................................................ 24

Location of Study Site and Surrounding Area .................................................................. 25

South Crescent Marsh Oblique Aerial Photos .................................................................. 26

Transect and Cross Section of South Crescent Marsh ...................................................... 27

Simplified Stratigraphy of All South Crescent Marsh Cores............................................ 28

APPENDIX A ............................................................................................................................... 29

Cores 1 - 4 ......................................................................................................................... 30

Cores 5 - 8 ......................................................................................................................... 31

Cores 9 - 12 ....................................................................................................................... 32

Cores 13 - 16 ..................................................................................................................... 33

Cores 17 - 18 ..................................................................................................................... 34

APPENDIX B ............................................................................................................................... 35

Survey Data ....................................................................................................................... 36

SAND DEPOISTION MECHANISMS IN HOLOCENE MARSH STRATIGRAPHY FROM A TSUNAMI PRONE LOCALITY, CRESCENT CITY, CALIFORNIA, SOUTHERN CASCADIAN MARGIN

- 1 -

INTRODUCTION

The Cascadia Subduction Zone (CSZ) is a ~1200 kilometer long convergent margin that

lies offshore roughly parallel to the Pacific coast and extends northward from Cape Mendocino,

California to Vancouver Island, British Columbia. The CSZ has generated at a minimum, seven

great (moment magnitude Mw ≥8) earthquakes over the last 2000 years (Atwater et al., 1995).

CSZ earthquakes vary in time ranging from 100 to 1200 years between subsequent quakes with

an average recurrence interval of approximately 500 years among sites that have a record dating

back 3500 years (Kelsey et al., 2005).

Coastal wetland and marsh stratigraphy along the CSZ exhibit evidence of tsunami

inundation and coseismic subsidence from tsunamis generated by great CSZ earthquakes (Clague

and Bobrowsky, 1994; Atwater et al., 1995). Anomalous sand sheets that are contained between

mud and peat are commonly interpreted to have been deposited by near-field tsunamis

coinciding with great earthquakes (Clague and Bobrowsky, 1994; Kelsey et al., 1998; Peters et

al., 2001). The last CSZ rupture took place on January 26, 1700. This great earthquake generated

a tsunami that inundated the Pacific coastline and deposited sand sheets which have been

identified in several coastal marshes from northern California to Vancouver Island (PG&E,

2002). More than 50 published studies have documented sites that contain confirmed or potential

geological evidence of tsunamis along the Pacific coast from northern California to Vancouver

Island (Peters et al., 2003). Several sites along the northern California coastline have identified

geologic evidence for tsunami inundation (Carver et al., 1996; Abramson, 1998; Garrison-Laney,

1998; PG&E, 2002; Patton, 2004).


- 2 -

Crescent City

Historically, great subduction zone earthquakes, such as those in Chile, Alaska,

Kamchatka, Japan, and Indonesia, have generated tsunamis that have inundated coastal areas far

from the earthquake’s epicenter (Atwater, 1995; Dengler and Magoon, 2006). Two far-field

tsunamis, one from Chile in 1960 and the other from Alaska in 1964, inundated the Crescent City

area (PG&E, 2002; Dengler and Magoon, 2006). The deposits from these two far-field tsunamis

were preserved as two thin distinct sand sheets in Sand Mine Marsh near Crescent City (Carver

et al., 1996).

In historic times, Crescent City has been the most tsunami-prone area on the west coast of

the United States (Dengler and Magoon, 2006). Thirty-one tsunamis have been recorded at

Crescent City since 1933, nine with amplitudes of 0.5 meters or larger (NGDC, 2009). The 1964

far-field tsunami from Alaska was the largest historic event, flooding 29 city blocks in Crescent

City and inundating Crescent Beach to an elevation of approximately 20 feet (Magoon, 1966;

Figure 2). Paleoseismic investigations of Crescent City and Lagoon Creek (south of Crescent

City) show evidence of at least six large events in the past 3500 years (Abramson, 1998;

Garrison-Laney, 1998; PG&E, 2002). These sites contain the most complete stratigraphic record

of tsunami inundation in the Crescent City area (PG&E, 2002).

Several tsunamis have been recorded at Crescent City (Carver et al., 1996), yet these

seismically induced sea-waves represent only one of several processes responsible for the

deposition of anomalous sand sheets into coastal wetlands and marshes. Three processes are

considered as candidate depositional mechanisms in near sea level coastal marsh settings: (1)

near-field tsunamis generated from the CSZ, (2) far-field tsunamis generated from within the

Pacific Rim, and (3) storm-waves caused by extreme climatic conditions. Coastal marsh


- 3 -

stratigraphy that includes multiple, laterally continuous sand sheets in wash-over settings may

contain sedimentary evidence of tsunami inundation as well as storm-wave run-up (Witter et al.,

1999). However, there is no published evidence for storm-wave deposits at Crescent City

(PG&E, 2002). An oblique aerial photo in figure 4 documents the emplacement of a sand sheet

deposited from a high energy marine event which was laid down in a coastal marsh near

Crescent City.

The objectives of the current study were to describe the stratigraphy of South Crescent

Marsh and to identify the candidate processes responsible for anomalous sand sheets in this

coastal freshwater marsh. Understanding the depositional mechanisms for the emplacement of

anomalous sands in coastal marshes will aid in the interpretation of marsh stratigraphy.

Setting

Research was conducted within the Redwood National Park at South Crescent Marsh

located approximately five kilometers south of Crescent City along Crescent Beach (Figure 3).

The study area is located on Quaternary Battery Formation (Qb) deposits directly west of the

Cretaceous-Jurassic Franciscan broken formation (KJfbf) (Aalto, 1981; Figure 3). A small

intermittent stream feeds into the eastern side of the marsh, underneath Bluff Road which is 3.8

meters above MHHW (mean higher high water is an average of higher high water height

observations over a period of 19 years for tidal datums), from approximately one kilometer

landward with its headwaters in the Franciscan Complex. An outlet to the ocean on the north-

west side of the marsh drains freshwater out onto Crescent Beach. A sandy beach berm 3.3

meters above MHHW separates the South Crescent Marsh from the ocean. The beach berm is

periodically breached by large storm events or times of higher discharge within the marsh,

exposing the marsh to sand deposition by high energy marine conditions (Figure 4).


- 4 -

METHODS

Selection of Study Site

South Crescent Marsh (Figure 5) is susceptible to sand deposition from near-field

tsunamis generated from the CSZ, far-field tsunamis generated within the Pacific Rim, and storm

wave wash-over caused by extreme climatic conditions. It represents a semi-protected wetland

that has a high potential for preserving episodes of sand deposition related to high energy events.

Near-field tsunamis have been detailed in Sand Mine Marsh by Carver et al. (1996) which is

located two kilometers to the north, adjacent to Crescent Beach in a similar setting (Figure 3). In

addition, South Crescent Marsh lies within the zone of inundation by the 1964 tsunami making it

a good candidate for far-field preservation (Magoon, 1966). Large drift logs, greater than 0.5

meters in diameter, were emplaced by the 1964 tsunami and spatially coincide with Magoon’s

tsunami debris line (Magoon, 1966). The low elevation (approximately at the MHHW line) and

close proximity to the ocean make South Crescent Marsh a susceptible setting for periodic

episodes of wash-over from extreme climatic conditions. Strandlines of small woody debris were

observed overtopping the edge of the beach berm.

Field Study

To investigate the stratigraphy at South Crescent marsh, 18 two centimeter diameter

gouge cores were extracted along a transect perpendicular to Crescent Beach. These one-meter-

long gouge cores were taken at closely spaced intervals to better asses the continuity of the

subsurface stratigraphy and to facilitate in layer correlations across the marsh. All core samples

were digitally photographed in sections and logged at one millimeter intervals. Stratigraphic and


- 5 -

sedimentologic evidence from the gouge cores were inspected by visual and tactile methods

(Table 1) and then recorded on field sheets that detailed sediment lithology, lithologic modifiers,

such as the presence of rip-up clasts or detritus, and the type of contact between each layer.

Sediment colors were interpreted in the field. The field sheets were then digitized later using

Adobe Illustrator (Appendix A). Core positions were recorded with a Garmin GPSmap 60Cx

handheld GPS device. With WAAS/EGNOS enabled, this device allowed for accuracy within

2.13 to 3.57 meters. All core locations are recorded in decimal degrees using NAD83 as the map

datum.

Using standard surveying equipment, a beach profile was created parallel to the gouge

core transect in order to connect positions of the gouge cores relative the beach topography

(Figure 5). This profile bisects the beach, adjacent beach berm, and marsh area starting from the

western most point and moving eastward perpendicular to the coastline. The MHHW line is

interpreted to be at the same elevation as the break-in-slope of the sandy beach berm which

corresponds to 2.6 meters above the survey’s starting point. At the Crescent City tidal station,

ID# 9419750, the diurnal range (difference in height between MHHW and MLLW) is 2.09

meters (NOAA-COOPS, 2009). For consistency, all elevation measurements use the MHHW

tidal datum which is set to 0 meters in this report.


- 6 -

RESULTS

The subsurface stratigraphy was mapped approximately 200 meters east from the western

most edge of the marsh. Coring was restricted to this area due to the impenetrable substrate

outside of the marsh area. Several reconnaissance cores were taken east of Bluff road to confirm

that the furthest extent of marsh deposits lay at the western side of Bluff road. However, the

corer could not penetrate deeper than 15 centimeters. Based on the 15 centimeter deposits and

highly indurated character, it is interpreted that South Crescent Marsh transitions to Quaternary

Battery Formation deposits with increasing landward distance and elevation gain east of the

marsh.

Sand was observed in every core taken from within South Crescent Marsh. Four laterally

continuous sand sheets were mapped out along with several other discontinuous sand layers

intermittently distributed across the marsh (Figure 6). The majority of cores at South Crescent

Marsh bottom out in either mud or muddy-peat deposits. Refer to Appendix A for detailed

illustrations of the marsh cores. Peaty-mud and muddy-peat layers generally get thicker in size as

the distance landward increases. Most peat layers were observed within the top most 60

centimeters of the gouge core samples. In some cores a distinctive light-grey mud layer used as a

marker bed was used to aid in layer correlations.

Stratigraphy

South Crescent marsh stratigraphy is represented by mud, muddy-peat, peaty-mud, peat,

and sand. A generalized description of each stratigraphic unit is included below and in Table 1.


- 7 -

Mud: Mud units are composed of 95% fine grained material with less than 5% organics. Mud

deposits range in color from light-grey to grey and brown to dark-brown. The organic material

observed within the mud contains fibrous roots, rootlets, and small black specks colored brown

to dark-brown, and black.

Muddy-peat: Muddy-peat layers contain 50% or more clay content than organics. It can range in

color from brown to dark-brown in color. Overall it appears that there are on average more

muddy-peat layers than peaty-mud deposits.

Peaty-mud: Peaty-mud layers contain 50% or more organic material in a clay matrix. It can vary

from brown to black-brown in color.

Peat: Peat at South Crescent marsh is composed of nearly all organic material. It consists of

matted organic fibers with small roots and rootlets and in some locations contains pieces of

woody debris. In situ roots are preserved where marsh vegetation is growing. Compaction of

peaty material varies but generally peat at or near the marsh surface is loosely packed together

while peat observed deeper in the core was denser. Peat varied in color from dark brown to light

brown hues.

Sand: Sand layers preserved at South Crescent marsh are similar in grain size and lithology to

that of the adjacent Crescent Beach sands. Sand layers at South Crescent marsh are generally

well-sorted and range in size from fine to medium grained sands but may contain larger lithic

fragments such as in core C7 (Appendix A). Sand layer(s) may be massive or contain rip-up


- 8 -

clasts of peat and muddy material. Organic material (roots, rootlets, woody debris) may also be

found within sandy layers.

Sand Sheets

From the 18 gouge cores taken, four continuous sand sheets (labeled I-IV; Figure 6) were

observed in the top meter of marsh sediment at South Crescent marsh. Tables 2 and 3 detail the

sand sheet and individual core attributes. Sand deposits contained in the marsh are similar in

texture and mineralogy to the adjacent beach berm and Crescent Beach sands, suggesting that the

sand deposits have a marine origin. The four sand sheets are discussed below in stratigraphic

order from youngest to oldest.

Sand Sheet I: Six of the 18 gouge cores taken at South Crescent marsh detail evidence of a

continuous sand sheet in the uppermost meter of stratigraphy. The sand deposits represent the

most recent deposition of sand at the western edge of the marsh. Sheet I extends 95 meters

eastward of the MHHW line. Sand thickness ranges from 1.5-19 centimeters. A general trend of

thinning landward is observed with the last trace of sand found at core 6 (Figure 6). Sheet I does

not show an increase in elevation with an increase in horizontal distance inland. This may be due

to its relatively short extent inland where deposits are blanketed over the inward sloping marsh

topography. Four abrupt (<5mm) and two sharp (5-10mm) basal contacts of sand deposits are

evident in the cores.

Sand Sheet II: Sheet II is the next continuous sand sheet underlying sheet I. Sheet II is found

within 12 of the 18 cores. This sand sheet extends 155 meters eastward of the MHHW line and is

observed between -25.5 and -71.5 centimeters beneath the marsh surface. Thickness of sand


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layers range from 0.5 to 15.5 centimeters. Sheet II thins landwards and pinches out at core 12.

Sand deposits rise in elevation as the distance increases eastward. Sand layers have seven abrupt,

two sharp, and three gradational (10-20mm) basal contacts.

Sand Sheet III: Sheet III is found in 15 of the 18 cores and extends 185 meters eastward of the

MHHW line. Sand layers range in size from 1.5 to 19 centimeters thick and are found between -

35 and -95.5 centimeters deep. The majority of basal contacts are abrupt (11), with three sharp

and one gradational contact detailed. Sheet III varies in thickness across the marsh as some

layers thin and thicken.

Sand Sheet IV: Sheet IV was captured in 16 of the 18 gouge cores. Sand deposits extend 212

meters eastward of the MHHW line across the marsh with the last sand layer observed at core 17.

Layers of sand ranged in thickness from two to 28.5 centimeters and were found between -35.5

and -129 centimeters below the marsh surface. Sand deposits rise in elevation as the distance

increases landward. Thickness of sheet IV varies between cores with some sheets thinning

between thicker adjacent deposits. 13 abrupt and two sharp basal contacts were detailed. Sheet

IV represents the deepest sand sheet captured by the one meter long gouge corer.

Sheet IV had discernable features which were used to aid in assessing lateral continuity between

cores. These features included a blue-grey appearance; sands that contained organic fragments of

wood, bark, roots, rootlets, and grass; included rip-up clasts of mud; and had larger sands that

were normally graded.


- 10 -

In summary, all four sand sheets have similar characteristics, such as texture, mineralogy,

lateral continuity, and display abrupt and sharp basal contacts. However, they differ in other

physical attributes. Only sand sheets II, III, and IV contain evidence of rip-up clasts. Only sand

sheet IV exhibits normally graded sands and is also 9.5 centimeters thicker in size than the

thickest deposits recorded for sand sheets I-III. Sand sheet I does not increase in height as the

distance inland increases while all the other sand sheets have a general trend of gaining elevation

across the marsh.


- 11 -

DISCUSSION

The objectives of the current study were to describe the stratigraphy of South Crescent

Marsh and to identify the candidate processes responsible for anomalous sand sheets in this

coastal freshwater marsh. From the 18 gouge cores, four well defined, laterally continuous sand

sheets (labeled I-IV) were mapped within the top meter of marsh sediment at South Crescent

Marsh. It is inferred from these observations that all of the sand sheets were deposited by high

energy marine waters. This limits the depositional mechanisms for the emplacement of these

anomalous sands at this coastal freshwater marsh to storm-wave run-up caused by extreme

climatic conditions and by tsunami inundation from near and far-field sources.

Sand Sheet I

Sand sheet I is interpreted as a potential high energy storm-wave deposit generated by the

wash-over effect created in part by extreme marine water conditions. This sand sheet lies at the

surface of the marsh stratigraphy and is located adjacent to a plume of sand emplaced by a

breach in the marsh beach berm (Figure 4, 5, and 6). However, it cannot be ruled out that this

sand sheet may have been deposited by a tsunami.

Sand Sheets II and III

Based on previous research conducted at Crescent City, there is a high potential for

preservation of a far-field tsunami deposit at South Crescent Marsh. Magoon’s map (1966;

Figure 2) of the 1964 tsunami inundation zone shows the outer edge of inundation extending

over South Crescent Marsh. Furthermore, Carver (1996) recorded the presence of the 1960 and

1964 far-field tsunamis at Sand Mine Marsh which is located 2 kilometers to the north along


- 12 -

Crescent Beach in a similar setting (Figure 3). One of the four sand sheets detailed at South

Crescent Marsh may represent the 1964 far-field tsunami. The best candidate would most likely

be sand sheet II or III. Sand sheets II and III are preserved relatively shallow in the marsh

stratigraphy suggesting recent deposition. They extend inland close to the edge of inundation

mapped by Magoon (1966). Sand sheets II and III contain evidence of rip-up-clasts and have

numerous abrupt basal contacts. These physical attributes provide the best evidence to suggest

that they represent the 1964 tsunami. However, it is difficult to say with certainly by relying

solely on physical attributes of the sand layers.

Sand Sheet IV

Sand sheet IV represents the best candidate for a near-field tsunami. It exhibits a

landward thinning of sand layers, contains normally graded sand layers, has abrupt basal

contacts, and harbors evidence of rip-up-clasts. Additionally, near-field tsunamis have been

documented at Sand Mine Marsh (Carver et al., 1996) and at Lagoon Creek to the south

(Abramson, 1998; Garrison-Laney, 1998). This is the thickest of all sand sheets captured by the

one meter long gouge corer.

Distinguishing between candidate processes for sand deposition in coastal marsh

stratigraphy has its difficulties. For example, tsunami and storm deposits have the same spatial

characteristics; they both thin in size and texturally get finer as the distance landward increases

(Nelson et al., 1996b). In addition, sand layers recorded in marsh stratigraphy do not contain

unique physical characteristics that could be used to clearly distinguish between depositional

mechanisms, such as tsunamis versus storm waves (Witter et al., 1999). This makes it nearly

impossible to identify a true depositional mechanism for the sand sheets based on physical


- 13 -

attributes alone. If sand sheet IV was deposited by a near-field tsunami, the only identified

source would be the 1700 AD earthquake (Satake et al., 1996).


- 14 -

CONCLUSION

The current study documented four laterally continuous sand sheets within the

stratigraphy of South Crescent Marsh. The marsh is a prime wash-over setting located at MHHW

behind a relatively small berm, therefore elevated ocean levels from both tsunamis and storms

have an equal chance of inundating this area. The candidate mechanisms responsible for the

deposition of these four sand sheets are (1) near-field tsunamis generated from the CSZ, (2) far-

field tsunamis generated from within the Pacific Rim, and (3) storm-waves caused by extreme

climatic conditions. Findings from this study cannot attribute with certainty which process

caused the deposition of each of the sand sheets. However, based on depth, lateral extent and

thickness of the sand sheets, and on comparison of the sand sheets with sheets at Sand Mine

Marsh to the north and Lagoon Creek to the south, I suggest that sand sheet I was storm

generated and sand sheet IV may have been deposited by the 1700 AD CSZ earthquake. Sand

sheet II and III could have been deposited either by storms or by the 1960 and 1964 far-field

tsunamis.

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Witter, R.C., Kelsey, H.M., Hemphill-Haley, E., 1999. Pacific storms, El Nino and tsunamis:

competing mechanisms for sand deposition in a coastal marsh, Euchre Creek, Oregon.

Journal of Coastal Research, 17(3), pp. 563-583.

- 18 -

LIST OF TABLES

- 19 -

Visual and Tactile Estimation of Lithology

TABLE 1. VISUAL AND TACTILE ESTIMATION OF LITHOLOGY

Lithology % Organics Color Notes Marsh Environment† Peat > 90% Light brown to dark-

brown Consists of matted organic fibers with small roots

and rootlets and in some locations contains pieces of woody debris.

Very high marsh or forest

Peaty-Mud > 50 - 90% Brown to black-brown to to red-brown

Consists of abundant roots and rootlets colored orange to red in a clay matrix. May be dense to spongy to loosely packed when dry. In some cores minor amounts of sand was observed.

High marsh

Muddy-Peat

< 50 - 5% Organics Brown to dark-brown, clay is light grey to grey

Consists of abundant roots and rootlets colored orange in a clay rich matrix. Clay may be grey in color. Some cores contained traces of sand. When dry is loosely packed and crumbles.

Transitional marsh

Mud < 5% Light grey to grey and brown to dark-brown

Organic material observed within the mud may contain fibrous roots, rootlets, and small black specks colored brown to dark-brown, and black.

Barren tidal flat

†Based on Fiedorowicz, 1997.

- 20 -

Sand Sheet Attributes from South Crescent Marsh

TABLE 2. SAND SHEET ATTRIBUTES FROM SOUTH CRESCENT MARSH

Sand Sheet Number of Cores†

Thickness of Sand (cm)‡

Depth in Core (cm)¥ Number of Basal Contacts¤ Eastward Extent of Sand (m)§

Abrupt Sharp Gradational From MHHW From Beach Berm

I 6 1.5-19 -14.5 to -32.5 4 2 - 95 80 II 12 0.5-15.5 -71.5 to -25.5 7 2 3 155 140 III 15 1.5-19 -95.5 to -35 11 3 1 185 170 IV 16 2-28.5 -129 to -35.5 13 2 - 212 197

Note: Total of 18 gouge cores. †Number of cores in which disturbance event was identified. ‡Range in sand thickness among cores, including sand mixed with peat, muddy peat, peaty mud, or mud. ¥Range in depth of disturbance event measured from basal contact and arranged lowest to highest MHHW elevation. ¤Quantity of cores that have abrupt (<5mm), sharp (5-10mm), gradational (10-20mm) basal contacts. §Eastward extent of sand relative to MHHW mark and to the top of South Crescent Marsh’s adjacent beach berm.

- 21 -

Individual Core Attributes

TABLE 3. INDIVIDUAL CORE ATTRIBUTES

Core ID # Estimated MHHW

Elevation (m)†

Distance East from MHHW

Mark (m)‡

Core Distance East from Top of Beach Berm (m)§

1 -0.09 43.36 28

2 0.05 54.36 39 3 -0.05 65.36 50 4 -0.15 75.36 60 5 -0.18 85.36 70 6 -0.15 95.36 80 7 -0.25 106.36 91 8 -0.24 115.36 100 9 -0.23 125.36 110 10 -0.35 135.36 120 11 -0.28 145.36 130 12 -0.10 155.36 140 13 -0.05 165.36 150 14 -0.03 175.36 160 15 -0.15 185.36 170 16 0.11 200.36 185 17 0.20 212.36 197 18 0.55 230.36 215

†Core elevations were extrapolated from a graph detailing distance vs. elevation of the marsh topography. ‡MHHW mark is located on the western flank of the marsh's adjacent beach berm. §Top of beach berm is 3.34 meters above MHHW.

- 22 -

LIST OF FIGURES

- 23 -

Tectonic Overview and Northern California Tsunami Sites

- 24 -

Magoon’s 1964 Far-Field Tsunami Inundation Map

- 25 -

Location of Study Site and Surrounding Area

- 26 -

South Crescent Marsh Oblique Aerial Photos

- 27 -

Transect and Cross Section of South Crescent Marsh

- 28 -

Simplified Stratigraphy of All South Crescent Marsh Cores

- 29 -

APPENDIX A

- 30 -

Cores 1 - 4

- 31 -

Cores 5 - 8

- 32 -

Cores 9 - 12

- 33 -

Cores 13 - 16

- 34 -

Cores 17 - 18

- 35 -

APPENDIX B

- 36 -

Survey Data

APPENDIX 2. SURVEY DATA†

Station # Horizontal Distance (m) MHHW Elevation (m) Notes

1 0.00 -2.60 Crescent Beach 10.00 -2.48 20.00 -2.30 30.00 -2.15 39.99 -1.97 49.99 -1.77 59.99 -1.54 69.99 -1.23 79.98 -0.88 89.97 -0.58 99.97 -0.25 109.97 -0.03 119.96 0.20 124.96 0.47 126.02 1.53 2 126.86 3.34 Top of Beach Berm 131.77 2.41 136.66 1.36 141.59 0.55 146.59 0.40 156.58 -0.14 166.58 0.04 176.58 -0.06 186.57 -0.14 196.57 -0.18 206.57 -0.14 216.57 -0.26 236.57 -0.24 246.57 -0.35 256.57 -0.29 266.57 -0.12 276.57 -0.06 286.57 -0.06

- 37 -

296.57 -0.15 306.57 0.08 316.57 0.14 326.57 0.27 336.57 0.47 346.56 0.61 356.56 0.73 366.56 0.89 376.56 1.14 387.56 1.39 398.54 1.92 406.54 2.19 412.52 2.61 416.39 3.63

3 420.39 3.78 Middle of Bluff Road

†Compiled data from survey transect A-A' across study site.

Documents

Graehl (2009) Sand deposition mech