A geological eco d o mul iple Pleis ocene sunami inunda ions
in an oceanic island: The case o Maio, Cape Ve de
JOS

EMADEIRA*†, RICARDO S. RAMALHO*†‡§, DIRK L. HOFFMANN¶,
JO
~
AO MATA*†and M

ARIO MOREIRA***
*Ins i u o Dom Luiz, Faculdade de Ci^
encias, Uni e sidade de Lisboa, Edi 
ıcio C1, Campo G ande,
1749-016 Lisboa, Po ugal (E-mail: [email p o ec ed])
†Depa amen o de Geologia, Faculdade de Ci^
encias, Uni e sidade de Lisboa, Edi 
ıcio C6, Campo
G ande, Lisboa 1749-016, Po ugal
‡School o Ea h Sciences, Uni e si y o B is ol, Wills Memo ial Building, Queen’s Road, B is ol BS8 1RJ, UK
§Lamon -Dohe y Ea h Obse a o y, Columbia Uni e si y, Come Geochemis y Building, PO Box 1000,
Palisades, NY 10964-8000, USA
¶Depa men o Human E olu ion, Max Planck Ins i u e o E olu iona y An h opology, Deu sche Pla z 6,
Leipzig 04103, Ge many
**Ins i u o Supe io de Engenha ia de Lisboa, R. Conselhei o Em
ıdio Na a o 1, Lisboa 1959-007, Po ugal
Associa e Edi o – Ped o Cos a
ABSTRACT
In he Cen al A lan ic a chipelagos – he Cana ies, Cape Ve de, Madei a and he
Azo es – sunamihaza diso en ega dedaslow,whencompa edwi ho he
ex eme wa e e en s such as hu icanes and s o ms. The geological eco d o
many o hese islands, howe e , sugges s ha sunami haza d may be unde es i-
ma ed, no wi hs anding being lowe han in a eas adjacen o subduc ion zones,
such as he ma gins o he Paci ic and Indian oceans. Mo eo e , sunamis in
oceanic islands a e gene ally igge ed by local la ge-scale olcanic lank col-
lapses, o which li le is known abou hei equency, making i di icul o es i-
ma e he p obabili y o a new occu ence. Pa o he p oblem lies in he ac ha
sunami deposi s a e usually di icul o da e, and ew islands in he wo ld exhi-
bi e idence o epea ed sunami inunda ion on a p o ac ed imescale. This
s udy epo s on he p esence o abundan sunami deposi s (conglome a es and
sands ones) on Maio Island (Cape Ve de) and discusses hei s a ig aphy, sedi-
men ological cha ac e is ics, p obable age and sunamigenic sou ce. Obse a-
ions indica e ha ou dis inc inunda ion e en s o a iable magni ude ook
place du ing he Pleis ocene. One o he sunami deposi s yielded a high-con i-
dence U/Th age o 78809 ka, which o e laps wi hin e o wi h he
73 7 ka age p oposed o Fogo olcano’s lank collapse, an e en known o
ha e had a signi ican sunami impac on nea by San iago Island. This shows
ha he Fogo sunami also impac ed Maio, esul ing in unups in excess o 60 m
abo e coe al sea-le el a ca 120 km om he sou ce. Two olde deposi s, possi-
bly linked o ecu en lank collapses o he Tope de Co oa olcano in San o
An ~
ao Island, yielded lowe -con idence ages o 479 o 390 ka and 360 o 304 ka.
A younge deposi (<78 ka) emains unda ed. In summa y, he geological eco d
o Maio exhibi s well-p ese ed e idence o epea ed sunami inunda ion, ein-
o cing he no ion ha sunami haza d is no so low a olcanic a chipelagos ea-
u ing p ominen and highly-ac i e olcanoes such as in Cape Ve de.
Keywo ds Cape Ve de, equency, ocean islands, sedimen s, sunami.
1
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s
Sedimen ology (2019) doi: 10.1111/sed.12612
INTRODUCTION
Oceanic islands a e exposed o a ious na u al
haza ds depending on hei geodynamic se ing
and geog aphical loca ion; hese include ol-
canic e up ions, ea hquakes, loods, d ough s,
s o ms, landslides and sunamis. Island popula-
ion cen es a e usually loca ed a he coas and
o en a low ele a ions, and a e hus highly ul-
ne able o ma ine inunda ions esul ing om
s o m wa es and su ges o om sunami impac .
In he Cen al A lan ic a chipelagos, sunami
haza d is o en ega ded as low, bu he geologi-
cal eco d sugges s ha his haza d has been
conside ably unde es ima ed. Despi e being
much lowe han on coas lines o oceans su -
ounded by ac i e subduc ion zones capable o
p oducing high-magni ude subma ine ea h-
quakes, examples om Maca onesia (a biogeo-
g aphic egion including he Cen al A lan ic
a chipelagos o he Azo es, Madei a, Sel agens,
Cana ies and Cape Ve de; Fig. 1A) show ha he
isk imposed o popula ions by his ype o na u-
al haza d may, in ac , be much highe han is
usually conside ed. Accoun s o his o ical
e en s and geological e idence o pas sunami
inunda ions a ec ing he islands, igge ed by
bo h local and dis al sou ces, exis in all o Mac-
a onesia (Wa d & Day, 2001; Pa a as-Ca ayannis,
2002; And ade e al., 2006; Gisle e al., 2006;
Pe ez-To ado e al., 2006; Giache i e al., 2011;
Pa is e al., 2011, 2017, 2018; Fe e e al., 2013;
Hun e al., 2013; Ramalho e al., 2015; Madei a
e al., 2016; Omi a e al., 2016). Fo example,
chao ic conglome a es ea u ing ma ine ossils
occu dispe sed along he slopes o Aga€
e e al-
ley in G an Cana ia, om 41 o 188 m in ele a-
ion, a es ing o signi ican sunami inunda ion
esul ing om he G€
u
ıma olcanic lank col-
lapse(s) in he nea by island o Tene i e, which
ook place some ime be o e 083 Ma (Pe ez-To -
ado e al., 2006; Giache i e al., 2011; Pa is
e al., 2018). Ano he example in he Cana y
Islands conce ns he Isla Baja and Teno Bajo
deposi s in no h-wes Tene i e, ound up o
132 m in ele a ion, which a es o he succes-
si e impac o wo consecu i e sunamis ig-
ge ed espec i ely by he Icod lank collapse and
Ab igo ignimb i e e up ion ca 170 ka; hese
deposi s indica e a scena io in ol ing a coupled
lank collapse and majo explosi e e up ion,
esul ing in ex eme sunami inunda ion o adja-
cen coas lines (Pa is e al., 2017, 2018). The
collapse o Fogo olcano, in Cape Ve de, is ye
ano he example o a sunamigenic e en ha
esul ed in a de as a ing impac o adjacen
coas lines. E ec i ely, ields o s anded mega-
clas s (up o 243 m
3
) and chao ic ma ine con-
glome a es occu in he adjacen island o
San iago, up o 220 m o ele a ion, a es ing o
he impac o a sunami igge ed by his col-
lapse a ca 73 ka (Pa is e al., 2011, 2018;
Ramalho e al., 2015; Ma 
ınez-Mo eno e al.,
2018). These deposi s imply sunami unups
exceeding 270 m along he no he n sho e o
San iago, once again con i ming he haza d
po en ial o olcanic lank collapses as nea - ield
sou ces o highly de as a ing sunamis (Ramalho
e al., 2015; Pa is e al., 2018).
Despi e he exis ence o ample e idence o su-
nami impac on se e al olcanic a chipelagos, a
key ques ion in he deba e abou he haza d and
isk posed by sunami inunda ion along he
coas lines o hese a chipelagos –by ei he
locally-sou ced collapse- igge ed sunamis o
emo ely-gene a ed sunamis –conce ns he e-
quency o such e en s. The es ima ion o i s e-
quency is c ucial o assess he suscep ibili y/
ulne abili y o coas al popula ions o sunami
inunda ion. A lack o a easonable knowledge
conce ning he equency o such e en s is
de i ed om se e al ac o s, namely he poo
p ese a ion o many o he deposi s (pa icula ly
deposi s om smalle -magni ude e en s), di i-
cul y in da ing se e al o hose deposi s (a p ob-
lem exace ba ed by he in insic ex eme la e al
a ia ion o acies), a iable coas al mo phology
p o iding di e en sedimen accommoda ion
space and, pe haps as he esul o he p e ious
ac o s, he a i y o ou c ops ha clea ly a es o
mul iple sunami inunda ion o he same coas -
line on a p o ac ed imescale. So a , Aga€
e e al-
ley (G an Cana ia) cons i u es one o he ew
loca ions a oceanic islands wo ldwide wi h e i-
dence o mul iple ex eme sunami inunda ions
o e a pe iod ha was long enough o allow he
deposi ion o allu ial conglome a es and he o -
ma ion o palaeosols in be ween e en s (Madei a
e al., 2011; Pa is e al., 2018). Success ul da ing
o indi idual deposi s a Aga€
e e alley, howe e ,
has p o ed elusi e, mos ly owing o he lack o
da eable ma e ial o o he poo p ese a ion o
he deposi s hemsel es, a ac ha has so a
hampe ed a solid es ima ion o he equency o
sunami inunda ion a a single island o island
g oup (Pe ez-To ado e al., 2006; Madei a e al.,
2011).
The geological eco d o Maio in he Cape
Ve des, howe e , may p o ide he pe ec place
o s udy he equency o sunami inunda ion a
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
2J. Madei a e al.
a single island. Owing o i s a id clima e, low
coas al mo phology and e y slow upli a e,
Maio o e s he pe ec condi ions o hos and
p ese e sunami deposi s, allowing also o
mo e ho ough compa a i e s udies be ween
sunamigenic and ma ine e ace deposi s, gi en
ha he la e a e also well-p ese ed on he
island. Acco dingly, his s udy analyzes he geo-
logical eco d o Maio and demons a es ha he
island exhibi s well-p ese ed e idence o mul-
iple sunami inunda ion on a p o ac ed ime-
scale, possibly making i a e e ence locali y
amongs oceanic islands o in es iga e he e-
quency o such ex eme e en s. As he cu en
Fig. 1. Loca ion, mo phology and geology o Maio. (A) Loca ion o he Maca onesian a chipelagos, ba hyme y/
al ime y om ETOPO1 Global Relie Model (Na ional Geophysical Da a Cen e /NESDIS/NOAA/U.S. Depa men
o Comme ce, 2011). (B) The loca ion o Maio Island wi hin Cape Ve de A chipelago, ba hyme y om Gene al
Ba hyme ic Cha o he Oceans (GEBCO, 2014) and al ime y om Shu le Rada Topog aphy Mission, 1 a c sec
scene (SRTM3). (C) Hillshade om a digi al ele a ion model (DEM) o Maio Island (o iginal da ase a 1 : 5000
scale; MAHOT, 2010), wi h main oponymy. (D) Geological map o Maio (adap ed om Se alhei o, 1970, and
S illman e al., 1982) o e hillshade om a DEM (MAHOT, 2010).
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 3
s udy demons a es, he s a ig aphic ela ions
be ween he abundan ou c ops o sunamigenic
sedimen s (conglome a es and sands ones) in
his island indica e he occu ence o ou dis-
inc inunda ion e en s o a iable magni ude,
which ook place du ing he Pleis ocene. This
s udy documen s hese deposi s including hei
s a ig aphic ela ions, ex u al cha ac e is ics,
basal ea u es and palaeocu en ma ke s. The
age o he deposi s is add essed by U/Th da ing
o co als sampled om hese deposi s. Possible
sou ces o hese sunamis a e also discussed
wi hin he con ex o Cape Ve de.
MORPHOLOGY AND GEOLOGICAL
SETTING OF MAIO
The island o Maio is one o he oldes in he
Cape Ve de A chipelago (Fig. 1A and B), possi-
bly ha ing eme ged abo e sea-le el du ing he
ea ly Miocene (Se alhei o, 1970; Mi chell e al.,
1983; Ramalho e al., 2010a). I belongs o he
Leewa d o Sou he n G oup o he Cape Ve des
and is loca ed be ween he islands o Boa is a
and San iago (Fig. 1B). Maio is a ela i ely small
(269 km
2
), ellip ically-shaped island, 25 km
long in he no h o sou h di ec ion by 15 km
eas o wes . The island, howe e , has been sig-
ni ican ly educed by ma ine ab asion and is
p esen ly app oxima ely hal o i s o iginal a ea.
The ex ension o he island’s no h shel indi-
ca es an o iginal no h–sou h dimension o ca
44 km. P esen ly, he island edi ice exhibi s a
azed mo phology cha ac e ized by low-lying li -
o al pla o ms, su ounding esidual elie s in
he cen e o he island (Fig. 1C). The li o al
pla o ms exhibi a s ai case mo phology ha
co esponds o Holocene li o al sal pans and a
se o Pleis ocene aised beaches a ele a ions o
2 o6m,8 o12m,15 o20m,30 o40m,55
o 65 m, 65 o 75 m and 80 o 100 m abo e p e-
sen sea-le el (apsl). The ma ine e aces a e
in e p e ed as open-shel o wa e-domina ed
beach deposi s (Ramalho e al., 2010a), in e e y
way simila o he p esen -day beaches ha su -
ound he island, bu which we e consolida ed
and aised by upli , which di e en ially
a ec ed mos Cape Ve dean Islands (Ramalho
e al., 2010b). The esidual elie s ise o low
ele a ions, o example Mon e Penoso wi h
430 m, he maximum ele a ion in he island,
Mon e Ba alha wi h 294 m and Mon e B anco
wi h 253 m. Coas lines a e usually sandy, com-
p ising ex ensi e beaches la e ally con ined by
low ocky blu s composed o ei he basal (s.l.),
limes ones, o consolida ed Pleis ocene beach
and dune deposi s, al e na ing wi h s e ches o
ocky coas line (pa icula ly on he eas e n
sho e), cha ac e ized by low cli s (<5 m). Beach
sand composi ion is highly bioclas ic, composed
mos ly o shell and hodoli h deb is, o en wi h
<10% o li hoclas s/mine oclas s in he mix u e
(Johnson e al., 2013; Ramalho e al., 2013).
Geologically (Fig. 1D), he island exhibi s a
basemen o med by an upli ed Ju assic–C e ac-
eous ocean loo sequence comp ising upli ed
No mal Mid Ocean Ridge Basal s (N-MORB) pil-
low la as o he Ba alha Fo ma ion, in ensely
in uded by dykes, o e lain by limes ones o he
Mo o Fo ma ion and shales o he Ca queijo
Fo ma ion (Se alhei o, 1970; De Paepe e al.,
1974; Be na d-G i i hs e al., 1975; S illman
e al., 1982; Az
ema e al., 1990). Conglome a es
(Co uja Fo ma ion) ep esen ing shoaling o he
island o e lie he sea loo sequence. This base-
men was in uded and de o med ( olded and
aul ed) du ing he Palaeogene by he successi e
in usion o plu ons, o ming he Cen al
Igneous Complex (Rep esas e al., 2012), com-
p ising gabb os (essexi es and py oxeni es) and
syeni es. P obably o he same age a e some a e
ca bona i e dykes. A basal ic (s.l.) olcanic
sequence o Miocene age, comp ising hyalo-
clas i es and pillow la as (Casas Velhas Fo ma-
ion) ep esen ing he seamoun and eme gen
s ages, subae ial conglome a es (Ped o Vaz Fo -
ma ion) and la a lows (Malhada Ped a and
Mon e Penoso o ma ions), uncon o mably o e -
lies he Cen al Igneous Complex and he Meso-
zoic sea loo sequence. The lowlands a ound
he esidual elie s a e ex ensi ely co e ed by
calca eni es and conglome a es om he aised
Pleis ocene beaches, aeolian sands ones (consol-
ida ed dune ields), allu ial ans, ac i e sand
dunes and sal la s (sabkha).
The deposi s epo ed in his s udy ha e been
o me ly classi ied and mapped as aised Pleis-
ocene beach deposi s by p e ious au ho s (e.g.
Se alhei o, 1970; S illman e al., 1982; Ramalho
e al., 2010a), no wi hs anding hei di e en and
dis inc i e ex u al and s a ig aphic cha ac e is-
ics. On close inspec ion, howe e , hese cha ac-
e is ics se hem apa om a ypical ‘no mal’
beach deposi . This wo k demons a es he
sunamigenic na u e o hese deposi s, p esen ing
also e idence o a mul is age o igin (based on a
ex u al and s a ig aphical analysis), and docu-
men ing he ela ionship be ween hese and he
adjacen ‘no mal’ aised beach deposi s.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
4J. Madei a e al.
METHODS
Field obse a ions
The sedimen s we e su eyed h ough de ailed
ieldwo k and mapped a he 1 : 25 000 scale.
The ex u e, s uc u e, s a ig aphy and hickness
o he deposi s we e desc ibed and measu ed,
and he na u e o hei indi idual componen s
analyzed. S a ig aphic columns we e p oduced
o selec ed ou c ops, using s anda d me hods.
Whene e palaeocu en ma ke s we e obse ed,
hese we e measu ed o in e anspo di ec ion.
A en ion was also dedica ed o he basal ea u es
displayed by he ou c ops, i.e. he geome y and
na u e o he s a ig aphic con ac be ween he
deposi s and he unde lying subs a e, as well as
dis inc i e ex u es a he base ( o example,
inclusion o ‘ ip-up’ clas s o he subs a um
wi hin he sunami deposi ). The deposi s we e
sampled o palaeon ological con en , bu i s
s udy will no be add essed he e.
Sedimen ological c i e ia used o iden i y
g a elly sunami deposi s
A de ailed analysis o he sedimen ological c i e-
ia used o iden i ying sunami conglome a es
and g a el beds on oceanic islands can be ound
in he ecen e iew by Pa is e al. (2018). In
gene al, sunami deposi s ypically man le he
opog aphy (e en on s eep slopes) and a e usu-
ally p ese ed as pa ches (len icula geome y)
a di e en ele a ions (Moo e & Moo e, 1984;
Moo e, 2000; McMu y e al., 2004a,b; Pe ez-
To ado e al., 2006; Pa is e al., 2011, 2017,
2018; Ramalho e al., 2015). Addi ionally, su-
nami conglome a es and g a el beds almos
in a iably exhibi chao ic ex u es, being ei he
clas o ma ix-suppo ed bu gene ally ea u ing
a mixing o sedimen s om di e en sou ces
edis ibu ed bo h inland and o sho e (i.e. e -
es ial and ma ine) (Pe ez-To ado e al., 2006;
Ramalho e al., 2015; Pa is e al., 2017, 2018).
G ain-size dis ibu ion is commonly highly
he e ogeneous, o en including la ge boulde s
‘ loa ing’ in ine conglome a ic o sandy
ma ixes and equen ly displaying a mix u e o
bo h well- ounded and angula boulde s/pebbles
(Moo e & Moo e, 1984; Moo e, 2000; McMu y
e al., 2004a,b; Pe ez-To ado e al., 2006; Pa is
e al., 2011, 2017, 2018). Deposi s a e o en o ga-
nized in subuni s sepa a ed by e osional uncon-
o mi ies o by di use bu ab up ansi ions;
ex eme la e al a ia ion o acies may be
p esen (Pe ez-To ado e al., 2006; Ramalho
e al., 2015; Pa is e al., 2017, 2018). Landwa d
ining and hinning o sedimen is a key ea u e
o sunami deposi s bu is no always easy o
iden i y gi en he deposi s’ ex eme a ia ion in
g ain sizes. Tsunami deposi s usually es o e
i egula e osi e basal con ac s and may exhibi
clas ic dykes injec ed downwa d in o he sub-
s a um (Pe ez-To ado e al., 2006; Pa is e al.,
2017, 2018). The p ese a ion o iable subae ial
subs a es benea h sunami deposi s and he
p esence o ip-up clas s o his subs a um, as
well as e e se g aded ac ion ca pe s, a e pa -
icula ly dis inc i e ea u es linked o sunami
inunda ion (Pa is e al., 2018). In e ms o
palaeon ological con en , sunami deposi s also
gene ally exhibi a mix u e o axa wi h di e en
ba hyme ical ecological zona ion, di e en
habi a s and di e en ypes o subs a e (e.g.
Massa i e al., 2009; Coello B a o e al., 2014;
Pa is e al., 2017), o en esul ing in highe bio-
di e si y indexes (Pa is e al., 2018). The only
bio u ba ion ound in sunami sedimen s depos-
i ed onsho e co esponds o oo conc e ions,
o med by subsequen plan coloniza ion a he
su ace o he deposi s.
In con as o he a o emen ioned cha ac e is-
ics, aised beach deposi s ypically show g ea
la e al con inui y alongsho e, es ing on wa e-cu
low-angle sho e pla o ms, o en close o o e en
abu ing agains he o me sho e angle ha ma ks
he maximum each o he high/s ill sea-le el
s and. Basal sho e pla o ms almos always co e-
spond o ha d subs a es, gi en ha so sub-
s a es a e a ely p ese ed by e e yday p ocesses
o wa e-cu ing (Ramalho e al., 2013; Pa is e al.,
2018). Sedimen a y sequences ypically exhibi
no mal g ading and, despi e he p esence o con-
glome a ic basal laye s in e p e ed as ‘ ansg es-
si e lag’, a ely exhibi boulde s o pebble-sized
sedimen s excep in well-s a i ied beds o well-
ounded boulde s/pebbles associa ed wi h clea
palaeo-channels o seawa d-di ec ed e igenous
deb is lows. Sedimen a y s uc u es a e hose
ypical o wa e-bea en sandy beaches, exhibi ing
e en and c oss-bedding and lamina ion (depend-
ing on which zone o he beach i co esponds
o), o swaley and/o hummocky c oss-lamina ion
in p ese ed s o m/highe ene gy sedimen s
deposi ed u he o sho e (Ramalho, 2011;
Mayo al e al., 2013). T ansi ion o aeolian s uc-
u es is equen ly ound in he uppe pa o
aised e aces, and i is o en possible o ollow
he en i e ypical beach p o ile along con inuous
exposu es ups eam p esen -day d ainage
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 5

channels (Ramalho, 2011). Bio u ba ion is pa a-
moun in p ese ed aised beach p o iles, as
desc ibed in de ail in Mayo al e al. (2013).
As shall be demons a ed in he ollowing sec-
ions, he s udied deposi s o Maio Island exhi-
bi cha ac e is ics ha con o m wi h hose
e e ed abo e as ypical o sunamii es and a e
a odds wi h hose o beach deposi s. Key sedi-
men ological c i e ia used o iden i y hese
deposi s as sunamii es a e also he e illus a ed
h ough ield pho og aphs, palaeocu en in o -
ma ion and s a ig aphic sec ions.
U anium/ ho ium (U/Th) da ing
Well-p ese ed co als we e chosen o da ing
pu poses and small sec ions we e cu and pol-
ished o isual inspec ion. The chosen p is ine
co al samples showed no isible indica ion o
ec ys alliza ion.
Subsamples o U/Th age de e mina ions we e
milled om p is ine, dense sec ions o he co als
using a hand-held den al d ill. The masses o
indi idual subsamples we e in he ange
be ween 2 mg and 5 mg. Chemical p epa a ion
ollowed a s anda d p o ocol (Ho mann, 2008)
and U/Th measu emen s we e pe o med on a
mul icollec o induc i ely-coupled-plasma mass-
spec ome e (MC–ICP–MS; Nep une; The mo
Fishe Scien i ic, Wal ham, MA, USA) a he
CENIEH (Cen o Nacional de In es igaci
on sob e
la E oluci
on Humana, Bu gos, Spain) ollowing
p ocedu es ou lined in Ho mann e al. (2007).
All ages we e calcula ed using he hal -li es
epo ed in Cheng e al. (2000) and a e he e
epo ed wi hin 2 o unce ain y.
RESULTS
Geog aphical dis ibu ion o he sunami
deposi s
Discon inuous sunami deposi s we e iden i ied
along mos o Maio’s li o al coas line and up o
7 km inland om he p esen -day coas line
(Fig. 2). Ou c op ele a ions (ob ained om
1 : 25 000 scale opog aphic maps and con-
i med wi h an al ime e ) ange om p esen -day
sea-le el up o 70 m apsl, as a es ed by a su-
nami deposi exposed in a qua y loca ed sou h
o he main oad 44 km o he ENE o Vila de
Po o Ingl^
es (si e 1 in Fig. 2; a N15.15515°,
W23.17500°). The sunami deposi loca ed u -
hes inland (7 km) is exposed in he uppe
eaches o Ribei a do Luga (si e 2 in Fig. 2; a
N15.25953°, W23.14935°), a ca 40 m in ele a-
ion. Local discon inui y o he ou c ops is in e -
p e ed o be ei he he esul o e osion o o
co e age by younge sedimen s. This is he case
along he sou h-wes coas , he longes s e ch
wi hou isible ou c ops, owing o he exis ence
o ex ensi e sal la s and a con inuous and wide
sandy beach wi hou ocky exposu es.
Al hough he base o he sunami deposi s is
o en sub-ho izon al, in some places hey co e
li o al and lu ial alley slopes (Fig. 3A o D).
Gene ally, he deposi s can only be ecognized
in c oss-sec ion exposu es (a coas al cli aces,
s eam banks, oad cu s and qua ies). A su ace
exposu es, a pe asi e ca bona ed pedogenic
al e a ion (calc e e) su ace makes i impossible
o dis inguish sunami om o he ca bona e
deposi s such as aised beach and consolida ed
aeolian sands ones (Fig. 3E).
S a ig aphy and s uc u e o he deposi s
The sunami deposi s a e amongs he mos ecen
geological uni s in he island and a e only co -
e ed by Holocene o Uppe Pleis ocene o ma-
ions (ac i e o consolida ed dune ields, allu ial
and sal - la deposi s, and beach sands in he case
o he olde sunami deposi ; Fig. 4A and B).
They o e lie all o he geological o ma ions
(Ju assic–C e aceous sea loo sequence, Miocene
subae ial and subma ine la a lows, Pleis ocene
aised beaches, consolida ed dunes, lagoon
sequences, palaeosols and allu ial an conglom-
e a es; Fig. 4C o G). The indi idual sunami
deposi s consis o one o h ee laye s
ep esen ing successi e low uni s, and ypically
s a wi h ma ix-suppo ed chao ic conglome -
a es (Fig. 4G). The hickness o indi idual uni s
anges om a ew decime es up o se e al (4 o 6)
me es. Fou di e en deposi s we e ecognized
in he island. In one key coas al sec ion no h-eas
o he Ba ei o i e mou h (si e 3 in Fig. 2; a
N15.12817°, W23.14037°), h ee sunami deposi s
a e supe posed in a con inuous ou c op (Fig. 5A
and B). All h ee deposi s exhibi e osional bases.
The lowe sunami deposi ( 1 in Fig. 5A) is dis-
con inuous and is ep esen ed by wo len icula
bodies illing palaeochannels on a basemen o
subae ial basal s om he Casas Velhas Fo ma-
ion; i is a ma ix-suppo ed, ining-upwa d, con-
glome a e composed o angula basal clas s (1 o
30 cm in diame e ), chao ically se in a bioclas ic
sandy-sil y ma ix, and exhibi ing ma ine ossils.
The e a e emains o a palaeosol de eloped on
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
6J. Madei a e al.
op o his deposi . The lowe and middle ( 1 and
2 in Fig. 5A and B) sunami deposi s a e sepa-
a ed by a 06 o09 m hick ed allu ial an
deposi , which o e lies a 08 o16 m hick beach
sands one laye . The middle sunami deposi ( 2)
is composed o wo laye s (laye s 4a and 4b in
Fig. 5A). The base is a discon inuous len icula
laye uncon o mably o e lying he allu ial an
and palaeosol, o es ing di ec ly on he beach
sands one, whe e he allu ial deposi was e oded.
I is a ossili e ous ( hodoli hs and molluscs)
ma ix-suppo ed o clas -suppo ed conglome -
a e made o angula basal clas s chao ically se in
a clay o sand ma ix (p obably he esul o mix-
ing be ween he allu ial an sedimen s and ma -
ine sands) and con ains ip-up clas s o he beach
sands one. I is less consolida ed han he uppe
laye , which s ands ou as an e osion- esis an
bed. The uppe laye o he middle sunami (uni
4b o 2 in Fig. 5) is a ossili e ous upwa d- ining
ma ix-suppo ed conglome a e composed o
angula basal agmen s (<20 cm) chao ically se
in a bioclas ic sand ma ix. Locally i displays a
palaeosol de eloped on op. This deposi is co -
e ed by a 07 m hick ed allu ial an deposi ,
which in u n is o e lain by he uppe sunami
deposi ( 3 in Fig. 5A and B). This sunami
deposi p esen s a wa y base ha co esponds o
palaeochannels ca ed on he unde lying allu ial
sedimen s. I is a single ossili e ous conglome -
a e laye wi h angula basal clas s suppo ed by a
bioclas ic sand ma ix. This deposi is iche in
ossils and sligh ly less consolida ed han he
lowe and middle sunami deposi s. The
sequence is co e ed by mode n ed allu ial an
conglome a es.
A ou h, younge sunami deposi ( 4)
occu s a he coas jus no h o he mou h o
Ribei a Funda de Cima (si e 4 in Fig. 2; a
N15.15102°, W23.10458°). This deposi co e s
a slope ha ex ends om he base o he sea
cli a 1 o 2 m up o 9 o 10 m apsl and cu s
he pla o m (a an ele a ion o 9 o 13 m) ha
suppo s one o he olde sunami deposi s
Fig. 2. Simpli ied map o he
sunami deposi s ecognized in he
Island o Maio (shaded in yellow:
da ke a eas –obse ed deposi s;
ligh e a eas –in e ed deposi s)
and main oponymy, o e hillshade
om a digi al ele a ion model
(MAHOT, 2010), numbe s ma k he
si es e e ed o in he ex and in
Table 1. U/Th ages o da ed co als
a e assigned o he espec i e
ou c ops.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 7
(p obably 1); i is a ma ix-suppo ed chao ic
conglome a e wi h angula clas s o MORB
basal and aeolian sands one se in a weakly
consolida ed bioclas ic sand ma ix (Fig. 3C).
This deposi is e y ossili e ous and some o
he gas opod shells s ill display colou . The
geome ic ela ion wi h he sunami deposi
ha c ops ou on he 9 o 13 m apsl pla o m,
he weak deg ee o consolida ion and he good
p ese a ion o he ossil con en sugges a
younge age when compa ed wi h he h ee
olde sunami deposi s.
A
BC
DE
Fig. 3. Field pho og aphs o sunami deposi s and hei ela ionship wi h he opog aphy. Map shows he loca ion
o he depic ed ou c ops. (A) Tsunami deposi o e lapping a slope a he igh bank o Casas Velhas c eek (base
ma ked by do ed line), in he a ield he ho izon al whi e deposi is a Pleis ocene aised beach (base ma ked by
dashed line). Leng h o ma ked sunami deposi is ca 80 m. (B) Tsunami deposi o e lapping a slope a he igh
bank o a c eek on he eas coas (base ma ked by do ed line, 14 m walking s ick o scale). (C) Pho og aph looking
upslope o he younge sunami ( 4) deposi (base ma ked by do ed line) o e lapping a coas al slope on he eas
coas , he la su ace in he backg ound is co e ed wi h an olde sunami (p obably 1; base ma ked by dashed line)
and he whi e cli behind is cu on a Pleis ocene aised beach deposi ( he isible pa o walking s ick is 12m).
(D) Geological ske ch showing he ela ion be ween sunamis 1 and 4. (E) Tsunami conglome a e exposed a he
coas sou h o Calhe a, wi h a 20 cm hick calc e e de eloped on op, he deposi is co e ed by a sandy collu ium.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
8J. Madei a e al.
A ano he loca ion in he sou h-eas coas
(si e 5 in Fig. 2; a N15.13639°, W23.12778°), an
ou c op a he sea cli exposes wo supe posed
sunami deposi s (Fig. 5C). The lowe sunami
sequence is o med by ou laye s (uni s 1a o
1d in Fig. 5C) dipping 16° o he no h (S
0
–
N80W,16N), i.e. landwa d, es ing on an e osion
su ace cu on MORB pillows, in uded by
dykes, om he Ba alha Fo ma ion. The land-
wa d dip o he lowe sunami sequence indi-
ca es ha i ossilized a no hwa d-dipping
palaeo opog aphy, a ea u e ha is ne e
obse ed in he case o ma ine e aces, which
in a iably es on gen le seawa d-dipping sho e
pla o ms. This sunami deposi s a s wi h a
chao ic coa se conglome a e, mos ly clas -sup-
po ed, comp ising angula basal clas s se in a
bioclas ic sand ma ix con aining hodoli hs and
oys e s; i is ollowed by h ee ining-upwa d
laye s o ossili e ous conglome a ic sil y-sands.
The uppe sunami deposi s ands di ec ly,
h ough an e osi e undula ed su ace, on he
lowe sunami deposi . This deposi consis s o
wo laye s (uni s 2a and 2b in Fig. 5C). The
basal laye is a ossili e ous ining-upwa d
ma ix-suppo ed conglome a e wi h a bioclas ic
sandy ma ix. Mos o he la ge clas s a e a he
base illing he e osi e palaeochannels, bu some
a e loa ing in he sandy ma ix, in chao ic posi-
ions. The la ge clas s consis o igneous ocks,
aeolian sands one, and ip-up clas s om he
unde lying sunami conglome a e. The base o
uppe laye is also e osi e, and he conglome a e
displays e e se g ading wi h he la ge blocks
on op. Igneous clas s a e dominan , and he ex-
u e is mos ly ma ix-suppo ed.
In all o he loca ions only one sunami deposi
is p esen , making i di icul o de e mine o
which e en i co esponds. The e a e, none he-
less, some indica o s such as he deg ee o li hi-
ica ion, dissolu ion o mollusc shells, o
co e age by consolida ed aeolian sands all
poin ing o an olde age o he deposi s. The
a ibu ion o he ou c ops o a de e mined su-
nami e en is in mos cases dependen on u -
he iso opic age de e mina ions.
The base o he deposi s is e osional in mos
cases (Fig. 6A o D), al hough la e ally he con-
ac may be appa en ly con o mable wi h he
unde lying uni s. The e osional ea u es include
palaeochannels and enches unca ing he
basemen o ma ions in bo h so and ha d ock,
o downwa d injec ed sedimen dykes. A Pon a
P e a beach, he p ocess o qua ying he sub-
s a e by he sunami was p ese ed in he
ex u e o he conglome a e, wi h ip-up clas s
o he unde lying beds loa ing in he conglom-
e a ic ma ix in he icini ies o he e osi e s ep
(Fig. 6D). The e, he sunami deposi o e lies a
25 o28 m hick lagoon sequence consis ing o
e igenous sands ones and consolida ed mud-
s one laye s exhibi ing bio u ba ion by ine
oo s. The sunami sedimen can be ound
injec ed in o he laye s o he lagoon sequence
along mechanical discon inui ies (sub e ical
join s and s a i ica ion su aces). These injec-
ions ac as wedges ha plucked blocks om he
unde lying laye . Blocks o hese cha ac e is ic
sedimen a y ocks a e ound inco po a ed
wi hin he o e lying sunami conglome a e
(Fig. 6D). So in aclas s o palaeosol, olcanic
u s, aeolian sands one and wea he ed la a a e
occasionally obse ed bu a e no abundan
(Fig. 6E).
Tex u e and composi ion o he deposi s
The sunamigenic sedimen s exhibi a bimodal
g anulome y co esponding o e y coa se con-
glome a es and sands ones con aining loa ing
pebbles, boulde s and blocks (Fig. 7A o G).
Some sands ones exhibi well-de eloped undu-
la ing hin lamina ion and include loa ing (i.e.
ma ix-suppo ed) boulde s (Fig 7D). The ex-
u e o he conglome a es can be ei he clas -
suppo ed o ma ix-suppo ed depending on
he amoun o ma ix. The ma ix o bo h he
conglome a es and sands ones is a medium o
coa se biogenic sand (Fig. 7C) dominan ly com-
posed o agmen s o calca eous algae (bu
also con aining agmen s o echinode m spi-
cules, mollusc shells and occasional o amini-
e a es s) wi h a mino ac ion o li hoclas s
(basal and calca eni e) and mine oclas s
(mos ly agmen s o py oxene c ys als). The
na u e o he boulde s and blocks is a iable
and depends on he geological uni s ha c op
ou in he su ounding a eas. These may
include blocks o olcanic ocks (subae ial and
subma ine basal s and dykes), a ious ypes o
sedimen a y ocks (lagoon muds ones and
sands ones, calca eni es om aised beaches,
consolida ed aeolian sands ones, o Mesozoic
limes ones) and plu onic ocks (gabb o). The
coa se ac ion includes bo h well- ounded
beach pebbles and boulde s and angula ock
agmen s (Fig. 7B and D). Some o he
ounded boulde s we e anspo ed inland om
he li o al as e idenced by he p esence o
a ached oys e s and bioe osion ea u es
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 9
A
BC
DE
FG
Fig. 8. Examples o he ossili e ous con en o he sunami deposi s. Map shows he loca ion o he depic ed ou c ops. (A)
La ge sha e ed block o ee co al (whi e do ed con ou ) a Ribei a do Luga c eek (geological hamme as scale). (B) Small
co al head a sunami ou c op a he eas coas (co al is 10 cm in diame e ). (C) and (D) Examples o ossil gas opods: ossil
(C) is 25 cm in diame e ; he limpe in (D) belongs o genus Fissu ella and is 35 cmindiame e .(E)Fossilo anechinode m
spicule (3 cm long). (F) and (G) Two di e en species o bi al es p esen ing a icula ed, closed al es. (F) Sample om Pon a
Pede nau on he no h coas (23 cm in diame e ). (G) Sample om he wes li o al sou h o Calhe a (7 cm in diame e ).
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
16 J. Madei a e al.

deposi s indica es ha he wa es o he sunami
e en s we e e ac ed a ound he island and ha
he inunda ions pene a ed signi ican ly inland
ac oss la land and climbing low-g adien slopes.
Sedimen sou ces and sedimen anspo
along he sho e
When he geology o he coas line a ies apidly,
he sunami deposi s may con ain boulde s o
li hologies ha do no c op ou in ha speci ic
locali y, implying along-sho e, landwa d o sea-
wa d anspo . Along he Ribei a P e a alley
(si e 8 in Fig. 2; a N15.14503°, W23.19338°) he
sunami deposi consis s o wo laye s: a basal
conglome a e up o 14 m hick, o e lain by a 4
o 6 m hick massi e sands one con aining big
blocks o columna -join ed subma ine basal ic
shee lows. The dimensions o 41 pa allel-
epipedal blocks we e measu ed, wi h majo axes
anging om 07 o46 m. In mos cases he
longe axis is pa allel o he join ing indica ing
he minimum hickness o he la a low om
which hey we e e oded. The sandy ma ix is
bioclas ic (ca bona ed), and hus o ma ine o i-
gin. The basemen he e co esponds o he Casas
Velhas Fo ma ion, which consis s o hyalo-
clas i es and isola ed pillow la as and does no
con ain shee lows. This ype o la a p esen ly
does no c op ou anywhe e onsho e, so he
blocks mus ha e been anspo ed no hwa d
along he alley om ou c ops p esen ly below
sea-le el, o om below he deposi i sel . This
assump ion is consis en wi h he low di ec-
ions obse ed a he coas .
An addi ional indica o o he inunda ion
di ec ion is gi en by he na u e o boulde s
included in he sunami conglome a es along
he eas sho eline. In ac , on h ee loca ions he
dominan na u e o he boulde s does no co e-
spond o he local basemen li hologies. Con-
e sely, he dominan composi ion o he clas s
ep esen s li hologies ha consis en ly only c op
ou u he sou h along he coas , implying a
no hwa d anspo , sligh ly oblique o he
coas . E ec i ely, inland om he dune o Pon a
do Mo o da A eia (si e 14 in Fig. 2; a
N15.15417°, W23.10167°), he sunami deposi
s ands on limes ones o Mo o Fo ma ion, whils
he dominan clas s in he sunami conglome a e
a e basal s om he Ba alha Fo ma ion, which
only c ops ou u he sou h. On ha same ou -
c op he sunami deposi injec s he basemen
limes ones along a na ow c ack ha dips 30° o
he NNE, a ea u e consis en wi h he deduced
inunda ion di ec ion. Fu he no h o Pon a do
Mo o da A eia (si e 15 in Fig. 2; a N15.15639°,
W23.09972°), he ela ion is he same; in depos-
i s o e lying limes ones o he Mo o Fo ma ion,
he dominan conglome a e boulde s a e basal-
ic. On he no h bank o Cimido lagoon (si e
16 in Fig. 2; a N15.16861°, W23.09778°), he
sunami deposi o e lies aeolian sands ones ha
co e a basemen o shales belonging o he Ca -
queijo Fo ma ion. A his loca ion, abou 50% o
he conglome a e boulde s a e limes one blocks
om he Mo o Fo ma ion, which only c ops ou
sou hwa d o his loca ion. These h ee ou c ops
he e o e exhibi e idence o alongsho e sedi-
men anspo om sou h o no h, compa ible
wi h he o ien a ion o he conglome a e boul-
de s a Ribei a de San a Cla a. This means ha
along he sou he n hal o he eas sho e o
Maio, he sunami inunda ed he island owa ds
a no hwa d di ec ion.
On he no h coas , he sunami deposi is
composed o ma ine bioclas ic sand (wi h abun-
dan ma ine ossils) and a coa se ac ion mos ly
composed o angula basal ic boulde s om he
Mon e Penoso Fo ma ion. Howe e , a ew blocks
o basal ic subma ine shee lows also occu in
he conglome a e. This li hology does no p e-
sen ly c op ou in he egion, so hese blocks o
subma ine la as mus ha e been picked up by
he sunami om a loca ion below p esen -day
sea-le el. The sand and ossils we e, hus, ans-
po ed inland om a sandy sho e, and he angu-
la boulde s we e picked up om he inunda ed
subae ial opog aphic su ace whe e hose
basal s c op ou .
Tsunami sou ces
The mos p obable sou ce o he sunami
deposi yielding an age o ca 79 ka is he lank
collapse o Fogo olcano (Pa is e al., 2011;
Ramalho e al., 2015). This age o 78809is
well wi hin he 65 o 84 ka age in e al and
compa ible, wi hin e o , wi h he mean age o
73368 ka epo ed by Ramalho e al. (2015)
on he basis o cosmogenic exposu e da ing o
he ields o megaclas s o no he n San iago,
which a e a ibu ed o he impac o a mega-
sunami esul ing om Fogo’s lank collapse.
Because he island o San iago s ands be ween
Fogo and Maio, he sunami wa es had o be
e ac ed a ound he conside able obs acle
o med by he island o San iago o hi Maio and
hen a ound Maio o lea e deposi s a he eas
coas o he island. Gi en ha sea-le el du ing
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 17
65 o 84 ka ( he age in e al epo ed o his
sunami; Ramalho e al., 2015) was 50 o 60 m
below p esen -day le el, he ele a ion (a leas
8 m) o his sunami deposi implies a minimum
unup in excess o 60 m abo e coe al sea-le el,
a a loca ion ha is a a dis ance o ca 120 km
A
BC
DE
FG
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
18 J. Madei a e al.
(as he c ow lies) om he sou ce o his su-
nami. The same sunami p oduced a minimum
unup o 270 m a he no h coas o San iago, a
a dis ance o 70 km om Fogo.
The e a e no con i med sou ces o he h ee
emaining sunami deposi s ( 1, 2 and 4) ound
on Maio. Howe e , onsho e and o sho e e i-
dence o la ge lank collapses abound in he
a chipelago, namely a San o An ~
ao, S~
ao Vicen e
and S~
ao Nicolau Islands (Le Bas e al., 2007; Mas-
son e al., 2008; Ancochea e al., 2010; Eisele
e al., 2015). Acco dingly, he wo olde sunami
deposi s could be associa ed wi h he wo known
lank collapses o he Tope de Co oa olcano in
sou h-wes San o An ~
ao, which may ha e aken
place a a ound 200 o 400 ka and >500 ka (Mas-
son e al., 2008). Bea ing in mind he p obable
ages epo ed by Masson e al. (2008), he o he
majo landslides in he Cape Ve de Islands (no h
and no heas San o An ~
ao, no h and sou h S~
ao
Vicen e, and no h and sou h S~
ao Nicolau) a e oo
old o accoun o he wo olde sunami deposi s
documen ed on Maio, assuming a maximum age
o 479 ka o hese deposi s. The ages ob ained o
Maio’s sunami e en 2 is compa ible wi h he
younge collapse o San o An ~
ao (Tope de Co oa
1), en a i ely da ed a 200 o 400 ka by Masson
e al. (2008). Mo eo e , he age ange displayed
by he co al samples collec ed on his deposi
(Fig. 11), oughly coincides wi h ma ine iso ope
s age 9 (MIS 9; 337 o 300 ka; Lisiecki & Raymo,
2005). This sugges s ha his sunami occu ed
du ing o soon a e his in e glacial. In a simila
ashion, he age o he olde sunami pa ially
o e laps wi h MIS 11c ( h ee peaks o empe a-
u e maxima a 425 ka, 420 o 412 ka and 407 ka;
Candy e al., 2014). This in e glacial co esponds
o a long (20 o 40 ka) wa m pe iod du ing which
he sea was close o Holocene le els (Candy e al.,
2014; Pas In e glacials Wo king G oup o
PAGES, 2016). The ac ha he clima e was
wa m, and he in e glacial pe iod long, may
accoun o he de elopmen o co al ee s on he
Maio coas . This could explain he la ge (me e-
sized) blocks o co al included in he Ribei a do
Luga sunami deposi s. P esen ly no co al ee s
exis in Maio and he ocky ou c ops in he coas
only display small enc us ing and occasional
b anching co als. Ano he signi ican aspec
obse ed in one o he Ribei a do Luga ou c ops
is ha he sunami deposi seems o co e a ocky
ab asion pla o m. This is sugges ed by a dyke
p o uding om ha su ace ha displays bioe o-
sion ea u es, blocks o which we e inco po a ed
in he sunami deposi and anspo ed eas wa d.
The bioe osion bo ings in he basal ic dyke indi-
ca e ha he su ace on which he sunami
deposi s ands was a o sligh ly below sea-le el.
Since he ou c op is p esen ly a an ele a ion o
ca 40 m apsl, i indica es an a e age upli o he
island o 01 mm yea
1
du ing he las 400 ka,
which is a a e compa ible wi h he upli econ-
s uc ions o Maio (Ramalho e al., 2010a,b,c).
The igge o his sunami is s ill unce ain, bu
he olde lank collapse o Topo de Co oa (Tope
de Co oa 2 o Masson e al., 2008) is a good candi-
da e, gi en he p oximi y (bu no o e lap)
be ween he age in e al yielded by 2 (479 o
390 ka) and he age in e ed (>500 ka; Masson
e al., 2008) o his collapse, pa icula ly aking
in o accoun he la ge unce ain y in he age es i-
ma es epo ed o hese landslides.
The beach–lagoon– sunami sequence o Pon a
P e a beach (si es 6 and 7 in Fig. 2) sugges s
ei he a sea-le el d op o coas al p og ada ion.
The beach sands one c ops ou in he p esen -
day sandy beach and sea-cli om sea-le el up
o ca 10 m apsl, while he op o he lagoon
sequence is a ca 14 m apsl. Conside ing he
age o 3971283 ka yielded by he co al sam-
pled om he beach sands one, he sea-le el
d op ollowing he MIS 11c high-s and could
accoun o his eg essi e sedimen a y
sequence. This age also means ha he o e ly-
ing sunami deposi s a e ela ed ei he o e en s
2 o 3.
Fig. 9. Pho og aphs o he di e en aspec s o di ec ional s uc u es displayed by he sunami deposi s. Map
shows he loca ion o he depic ed ou c ops. (A) and (B) Imb ica ed clas s a he base o sunami conglome a es
indica ing in low (coas is o he le ) a he igh bank o Casas Velhas c eek –po ion o walking s ick isible in
(A) is 1 m long; geological hamme o scale in (B) is 33 cm long. (C) and (D) Imb ica ed la clas s in sunami con-
glome a es indica ing up ush (C) and backwash (D) a he le bank o Cumeazo c eek –coas o he igh in bo h
pho og aphs; yellow ule in (C) is 20 cm long; geological hamme o scale in (D) is 33 cm long. (E) O ien ed la
clas s in sunami conglome a e indica ing cu en s om he no h ( egion o Laje B anca Isle , geological hamme
o scale). (F) G oo es a he base o he sunami conglome a es o Pon a P e a beach indica ing a no h–sou h cu -
en (13 cm long pen o scale and o indica e cu en di ec ion). (G) Linea ions in lamina ed sands one laye om
he sunami deposi s o Casas Velhas c eek alley in e p e ed as low s uc u es (pen o scale and o indica e
cu en di ec ion). Whi e a ows in pho og aphs (A) o (E) indica e cu en di ec ion.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 19
Fig. 10. S e eog aphic plo s o he o ien ed and imb ica ed boulde s, g oo es and linea ions desc ibed in he ex
(and in Appendix S1) and espec i e loca ions o e he hillshade om a digi al ele a ion model o Maio
(MAHOT, 2010). (A) Pon a P e a beach da a wi h o ien ed clas s in blue (blue a ow indica es cu en sense and
associa ed azimu h) and g oo es and lu e cas s in ed (black a ow). (B) and (C) O ien ed clas s (B) and linea ions
(C) measu ed a Casas Velhas alley a he ou c op close o he sho e. (D) o (F) S e eog aphic plo o da a om
wo nea by ou c ops ups eam om (B) and (C) along Casas Velhas alley –(D) and (E) co espond o he lowe
and uppe pa o he same ou c op, showing in low and backwash. (G) Da a om o ien ed la clas s ( ed do s
and black a ow) and imb ica ed clas s (blue do s and blue a ow) om Cumeazo alley. (H) Da a om he coas
nea Pil~
ao C~
ao. (I) Da a om o ien ed la clas s om he coas eas o Laje B anca isle wi h he ose diag am
showing a dominan SSW–NNE di ec ion and a ain e NNW–SSE di ec ion. (J) Da a om la clas s a Pon a Ped-
e nau coas wi h he la ge dispe sion co esponding o in low om bo h he NNW and om he WSW ( ed do s)
and some blocks o e u ned by backwash (blue do s). Dip and dip di ec ion o la clas s, g oo es and linea ions
we e p ojec ed as lines ( ep esen ed as poin s in he plo s), lowe hemisphe e s e eog aphic p ojec ions p oduced
wi h GEORIENT, e sion 9.5.1; GEORIENT, 2015.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
20 J. Madei a e al.
Finally, he younges o he sunami deposi s
( 4) only c ops ou a one loca ion. The e o e, i
seems o be he esul o a e y localized e en
and may ha e been p oduced by a local sub-
ma ine landslide (on he sou h-eas subma ine
lank o Maio?), o by a smalle landslide a
Fogo, ollowing he main e en a 73 o 79 ka.
Final ema ks
No wi hs anding he s ill incomple e knowledge
o he likely sou ces and he need o mo e p ecise
ages o hese e en s, he geological eco d shows
ha he island o Maio was impac ed by ou su-
nami inunda ions in he las ( ou ?) hund ed hou-
sand yea s, h ee o which p oduced signi ican
inunda ion. This cons i u es e idence o mul iple
sunami inunda ions wi hin a p o ac ed ime-
scale, wi h a mean equency o one e en e e y
100 ka. Combined wi h examples om o he
a chipelagos (see Pa is e al., 2018, o a e iew),
he indings epo ed he e ein o ce he no ion
ha sunami haza d is high a mos olcanic a chi-
pelagos, including hose loca ed in oceans su -
ounded by dominan ly passi e ma gins. Indeed,
olcanic islands can g ow quickly p oducing
s eep mo phologies and ab up lanks, which a e
g a i a ionally uns able, being p one o ail. This
is especially ue o a chipelagos ha s ill ea u e
p ominen and highly ac i e olcanoes ha may
one day collapse (again) as is he case o Fogo and
Tope de Co oa in Cape Ve de, Tene i e, La Palma
and El Hie o in he Cana y Islands, o Pico in he
Azo es. Islands wi h ex ensi e coas al lowlands
such as Maio a e pa icula ly ulne able o
Table 1. Loca ion o he samples analyzed by U/Th.
Si e
No.
Field
Re e ence N La . W Long.
Ele a ion
(m)
1 CVP116 15.15528°23.17500°70
2 CVP71a 15.25917°23.14983°39
2 CVP100a 15.25944°23.14944°40
2 CVP142a 15.25944°23.14944°40
2 CVP142b 15.25944°23.14944°40
4 CVP128 15.15111°23.10472°4
7 CVP77 15.12608°23.20255°1
17 CVP135 15.30944°23.12888°1
18 CVP95 15.31222°23.12111°4
18 CVP138 15.31222°23.12111°6
19 CVP122 15.12250°23.14722°3
19 CVP123 15.12250°23.14722°4
20 CVP127 15.20500°23.09416°10
21 CVP129 15.21805°23.09444°3
Table 2. Resul s o he U/Th analyses o co als om Maio: n.d. = no da a.
Lab ID Sample
238
U
(ng g
1
)
232
Th
(ng g
1
)
230
Th
(ng g
1
)
[
230
Th/
232
Th]
ac i i y a io
(
232
Th/
238
U)
ac i i y a io
(
230
Th/
238
U)
ac i i y a io
(
234
U/
238
U)
ac i i y a io
Age
(ka)
(
234
U/
238
U)
ini ial
ac i i y a io
UTO221 CVP129 2478013039489 0573 2353E-02 124E-03 4630441253E-03 1310E-05 5801E-01 4239E-03 1117E+00 2117E-03 7880911457 00026
UTO197 CVP123 2850316292790 0173 4789E-02 275E-03 320532753202E-04 3071E-06 1026E+00 6557E-03 1065E+00 2423E-03 316112311597 00062
UTO218 CVP138a 2747021421162 0179 4629E-02 362E-03 7436710431384E-04 8272E-06 1029E+00 4821E-03 1061E+00 2634E-03 332011611555 00057
UTO192 CVP127 2511421120096 0042 4298E-02 371E-03 83588951401251E-05 1967E-06 1046E+00 6203E-03 1071E+00 3125E-03 338515111848 00077
UTO219 CVP135 2705315900202 0064 4610E-02 268E-03 42579032762445E-05 4323E-06 1041E+00 5150E-03 1067E+00 2470E-03 339312511749 00062
UTO220 CVP95 23959179213241 0987 4130E-02 311E-03 5823441808E-03 1587E-05 1053E+00 5576E-03 1075E+00 2348E-03 344113511976 00071
UTO216 CVP122 3078911821806 0124 5234E-02 222E-03 541035721920E-04 5261E-06 1039E+00 4074E-03 1062E+00 1937E-03 348810911655 00050
UTO196 CVP77 165508807210 0412 2662E-02 131E-03 6893551425E-03 1198E-05 9825E-01 6145E-03 1007E+00 2487E-03 397128310204 00070
UTO195 CVP71a 233499690097 0015 3783E-02 180E-03 73075953401354E-05 9697E-07 9897E-01 5445E-03 1008E+00 2326E-03 422332010261 00068
UTO198 CVP142a 260267080172 0010 4227E-02 119E-03 45911543702161E-05 6896E-07 9921E-01 6255E-03 1009E+00 2403E-03 423736110314 00071
UTO217 CVP128 2674210881589 0096 4658E-02 176E-03 547496941944E-04 5047E-06 1064E+00 4662E-03 1063E+00 2061E-03 424724012085 00121
UTO194 CVP100a 2545515654274 0276 4188E-02 256E-03 182951405494E-04 4994E-06 1005E+00 4995E-03 1017E+00 2480E-03 442835910577 00073
UTO193 CVP116 241910732846 1444 4089E-03 184E-04 232024443E-02 3540E-04 1033E+00 7987E-03 1021E+00 5552E-03 Ou o ange
UTO222 CVP142b 277861005 n.d. 4665E-02 165E-03 1026E+00 3716E-03 1015E+00 1701E-03 Ou o ange
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
Mul iple sunami inunda ions in Maio Island 21

sunami inunda ion, which may a ec a eas up o
se e al kilome es inland. In Cape Ve de his is
he case o Boa Vis a, Sal and S~
ao Vicen e (in
addi ion o Maio i sel ), which a e islands wi h
g owing coas al occupa ion as a esul o a s eady
inc ease in ou ism.
CONCLUSIONS
Resea ch on sunami deposi s om he geologi-
cal eco d o olcanic oceanic islands, including
hei p obable age and sou ce, is c ucial o es i-
ma e he equency and magni ude o hese low-
p obabili y, high-impac e en s, and o assess
he h ea posed by such ex eme geohaza ds o
island popula ions. In his s udy, he occu ence
o abundan sunami deposi s on he geological
eco d o Maio Island is epo ed, wi h key ind-
ings ha a e summa ized he e:
1Sedimen a y deposi s assigned o sunami
deposi ion occu a mul iple places along he
coas o Maio island, being ound up o 70 m in
ele a ion, and up o ca 7 km inland om he
p esen -day coas line.
2The geological eco d o Maio a es s o he
p esence o possibly ou dis inc e en s o su-
nami inunda ion a a p o ac ed imescale, du -
ing he Pleis ocene.
3Based on U/Th da ing o co als sampled in
hese deposi s, one o he e en s yielded an age
o 78 09 ka, which o e laps wi hin e o wi h
he ca 73 7 ka mega sunami igge ed by he
lank collapse o Fogo olcano, an e en ha le
ample e idence o i s impac on he nea by
San iago Island (Pa is e al., 2011; Ramalho
e al., 2015). Two olde sunami e en s a e en-
a i ely da ed a 479 o 390 ka and 360 o
304 ka, da es ha a e compa ible wi h lank col-
lapses a Tope de Co oa in San o An ~
ao (Masson
e al., 2008), hus sugges ing ha his olcano is
a possible sou ce o hese e en s. A younge
(<79 ka), smalle e en emains unda ed.
4The p esence o sunami deposi s co ela i e
o he Fogo lank collapse implies a local unup
o his e en in excess o 60 m abo e coe al
sea-le el, a a dis ance o ca 120 km om he
sunamigenic sou ce.
5The geological eco d o Maio Island hus
exhibi s well-p ese ed e idence o epea ed su-
nami inunda ion, making i ano he e e ence
locali y amongs oceanic islands o in es iga e
he equency o such ex eme e en s. I also high-
ligh s ha low-lying islands a e pa icula ly ul-
ne able o sunami inunda ion, and how sunami
haza d assessmen s o olcanic a chipelagos
should conside such low-p obabili y, high-
impac e en s.
ACKNOWLEDGEMENTS
This wo k bene i ed om discussions wi h col-
leagues M
a io Cach~
ao, C
esa And ade and Ped o
Cos a. This is a con ibu ion om p ojec s CV-
PLUME (PTDC/CTE-GIN/64330/2006), MEGA
WAVE (IF/01641/2015) and UID/GEO/50019/
2013 o Ins i u o Dom Luiz, unded by FCT –
Fundacß
~
ao pa a a Ci^
encia e Tecnologia (Po ugal).
The suppo o colleagues om he Ins i u o
Nacional pa a a Ges ~
ao do Te i 
o io (INGT) and
Ins i u o Nacional de Me eo ologia e Geo 
ısica
(INMG) o Cabo Ve de, as well as he suppo o
colleague Jai Rod igues, is much app ecia ed.
We acknowledge he con ibu ions by he Associ-
a e Edi o Ped o Cos a, and F ancisco Pe ez-
Fig. 11. Plo o he se o U/Th co al da es by age and ele a ion; sampling si es a e iden i ied by colou s shown
in he inse legend, ho izon al ba s show he age unce ain y a he 2-sigma le el, ele a ion ange o he deposi s
is depic ed by e ical ba s and ci cles a e posi ioned a he sampling ele a ion. The age o si e 4 (ma ked wi h an
as e isk in he inse legend) ep esen s a co al sampled om sunami 4, which was p obably ewo ked om su-
nami 1 and he e o e is no indica i e o he ue age o deposi ion o 4.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
22 J. Madei a e al.
To ado, Raphael Pa is and an anonymous
e iewe o hei ca e ul e ision ha helped o
subs an ially imp o e he o iginal manusc ip .
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Manusc ip ecei ed 28 Sep embe 2018; e ision
accep ed 2 Ap il 2019
Suppo ing In o ma ion
Addi ional in o ma ion may be ound online in he
Suppo ing In o ma ion sec ion a he end o he
a icle:
Appendix S1. De ails o he di ec ional s uc u es
obse ed in Maio’s sunami deposi s.
©2019 The Au ho s. Sedimen ology ©2019 In e na ional Associa ion o Sedimen ologis s, Sedimen ology
24 J. Madei a e al.