Volcanism on the seafloor may account for >75% of all global volcanic activity. As we continue to increase exploration of the seafloor, we learn more about volcanic activity miles below the ocean's surface and the make-up of the oceanic crust.
Samuel's research aims to understand how submarine eruptions differ from those on land, and how deep volcanic activity can still have impacts at or near the surface.
Eruption dynamics and submarine clast cooling
Microtextures of volcanic rocks (glass, crystals and vesicles) can be used to interpret styles and intensity of volcanic eruptions on the seafloor. Measurements of hydroxyl (OH) in volcanic glass can be used to identify clast quenching conditions (pressure and temperature) as shown within previous research.
Vesicle and microlite size distributions and number densities have been used to interpret shallow conduit conditions, magmatic decompression, and how large pumice blocks are produced during submarine eruptions. A recent study also compared tube and spherical vesicles in pumice to assess strain conditions within a submarine volcanic conduit.
Other research has focused on fragmentation mechanisms of the 2012 eruption of the Havre submarine volcano, showing how pumice is produced in a "non-explosive" style as magma had insufficient cumulative strain or viscosity to result in magmatic fragmentation.
Secondary hyrdation of volcanic glass
Measurements of H2O in volcanic matrix glasses and melt inclusions are commonly used to interpret magma storage depths, magma ascent rates, processes within the shallow conduit, and clast quenching. However, these geochemical records can be altered by diffusion of external water into glass over a range of timescales and temperatures.
Previous research used H2O speciation (molecular H2O and OH), acquired by FTIR spectroscopy, to show how rapid rehydration can be identified in submarine glasses. High molecular-H2O/OH ratios can be used as a proxy for rehydrated glasses, and H2O diffusion profiles can be used to determine likely timescales of rehydration if quenching temperatures are known.
However, H2O speciation does not identify the source of rehydration, so we must rely on isotopic measurements of H and O in glass. More recent research (in revision) uses D/H measurements to identify multiple sources of H2O within submarine glasses from a variety of ages, eruptive styles and depths. Measurements of 18O/16O from silicate, and water in glass, can be used as a geo-thermometer to identify likely temperatures of rehydration.
Why do pumice sink or float in water?
Research currently in review compares clasts within oceanic pumice rafts with clasts taken from the seafloor produced by the same eruption. Subtle difference in microtextural properties (vesicle connectivity, pore throat diameters, and vesicle number densities) ultimately control how gas may become trapped within pore space in pumice.
Previous research by colleagues demonstrated experimentally that large volumes of gas can be trapped within high porosity pumice. The connectivity of pore space also controls how water in ingested into pumice and how vapor may escape during submarine pyroclast cooling.
Future research will aim to constrain how submarine clast textures may be identifiable from subaerial pumice microtextures, which helps with identifying paleoenvironments in ancient pyroclastic sequences.
Volcanoes katika bahari inaweza kuwa na jukumu kubwa zaidi ya 75% ya shughuli zote za volkano duniani. Kwa kuongezeka kwa uchunguzi wa bahari, tunajifunza zaidi juu ya shughuli za volkano maili chini ya uso wa bahari na muundo wa ganda la bahari. Utafiti wa Samuel unakusudia kuelewa jinsi milipuko ya chini ya maji inatofautiana na ile ya nchi kavu, na jinsi shughuli za volkano za kina kina vinavyoweza kuwa na athari kwenye au karibu na uso. Microtextures ya miamba ya volkano (kioo, fuwele na vesicles) inaweza kutumika kutafsiri mitindo na nguvu ya milipuko ya volkano juu ya sakafu ya bahari. Vipimo vya hydroxyl (OH) katika kioo volkano inaweza kutumika kutambua hali clast quenching ( shinikizo na joto) kama inavyoonyeshwa katika utafiti wa awali. Ugawaji wa ukubwa wa vesicle na microlite na wiani wa idadi zimetumika kutafsiri hali ya mifereji ya chini, decompression ya magmatic, na jinsi vitalu vikubwa vya pumice vinazalishwa wakati wa milipuko ya chini ya maji. Utafiti wa hivi karibuni pia ulilinganisha vifuniko vya bomba na vya mviringo katika mawe ya pumice ili kutathmini hali ya mvutano ndani ya mfereji wa volkano ya chini ya maji. Utafiti mwingine umezingatia utaratibu wa kugawanyika kwa milipuko ya 2012 ya volkano ya chini ya maji ya Havre, ikionyesha jinsi pumice inavyotengenezwa kwa mtindo wa "si-mlipuko" kwani magma haikuwa na mvutano wa kutosha au viscosity kusababisha kugawanyika kwa magmatic. H2O katika glasi za matrix ya volkano na inclusions ya kuyeyuka hutumiwa kwa kawaida kutafsiri magma ya kuhifadhi kina, magma viwango vya kupanda, michakato ndani ya mfereji wa chini, na clast quenching. Hata hivyo, rekodi hizi za kijiokemia zinaweza kubadilishwa na kuenea kwa maji ya nje ndani ya kioo kwa muda na joto. Utafiti wa awali ulitumia H2O speciation (molekuli ya H2O na OH) iliyopatikana na spectroscopy ya FTIR kuonyesha jinsi rehydration ya haraka inaweza kutambuliwa katika glasi za chini ya maji. Kiwango cha juu cha molekuli ya H2O inaweza kutumika kama proxy kwa glasi rehydrated, na maelezo ya kuenea ya H2O inaweza kutumika kuamua muda wa uwezekano wa rehydration kama joto la kuzima linajulikana. Hata hivyo, H2O speciation haijui chanzo cha rehydration, hivyo ni lazima kutegemea vipimo isotopic ya H na O katika kioo. Utafiti wa hivi karibuni (katika marekebisho) hutumia vipimo vya DH kutambua vyanzo vingi vya H2O ndani ya glasi za chini ya maji kutoka umri mbalimbali, mitindo ya mlipuko na kina. Kwa mfano, kipimo cha 18O16O kutoka kwa silicate na maji katika kioo inaweza kutumika kama thermometer ya kijiografia ili kutambua joto la uwezekano wa rehydration. Kwa nini mawe ya pumice huanguka au kuelea majini? Utafiti unaofanyiwa sasa unalinganisha vipande vya ndani vya miamba ya pumu ya baharini na vipande vilivyotokana na sakafu ya bahari vilivyotokezwa na mlipuko huohuo. Tofauti ndogo katika mali ya microtextural (kuunganisha vesicle, pore koo kipenyo, na vesicle idadi wiani) hatimaye kudhibiti jinsi gesi inaweza kuwa wamekamatwa ndani ya nafasi pore katika pumice. Utafiti wa awali uliofanywa na wenzake ulionyesha kwa majaribio kwamba kiasi kikubwa cha gesi kinaweza kukamatwa ndani ya mawe yenye umbo la mviringo. Uunganisho wa nafasi ya pore pia udhibiti jinsi maji katika kumeza katika pumice na jinsi mvuke inaweza kutoroka wakati wa submarine pyroclast baridi. Utafiti wa baadaye utahusisha jinsi textures ya clast ya chini ya maji inaweza kutambuliwa kutoka kwa microtextures ya pumice ya chini ya hewa, ambayo husaidia kutambua paleoenvironments katika mfululizo wa zamani wa pyroclastic.