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[1] We collected 56 marine gravity cores from the Pacific seafloor offshore Central America which contain a total of 213 volcanic ash beds. Ash-layer correlations between cores and with their parental tephras on land use stratigraphic, lithologic, and compositional criteria. In particular, we make use of our newly built database of bulk-rock, mineral, and glass major and trace element compositions of plinian and similarly widespread tephras erupted since the Pleistocene along the Central American Volcanic Arc. We thus identify the distal ashes of 11 Nicaraguan, 8 El Salvadorian, 6 Guatemalan, and 1 Costa Rican eruptions. Relatively uniform pelagic sedimentation rates allow us to determine ages of 10 previously undated tephras by their relative position between ash layers of known age. Linking the marine and terrestrial records yields a tephrostratigraphic framework for the Central American volcanic arc from Costa Rica to Guatemala. This is a useful tool and prerequisite to understand the evolution of volcanism at a whole-arc scale.

A Pliocene submarine series of alkali basaltic pillow lavas, hyaloclastites, and breccias (A), a sheeted dike swarm (B), and a basal suite of gabbro and ultramafic rocks (C) from La Palma (Canary Islands) is interpreted as a cross section through an uplifted seamount. This series has been tilted to its present orientation of 50ø/230 ø (plunge and azimuth), probably by upwarping due to intrusions in the central portion of the island. The basal plutonic complex (C) also includes intrusives coeval with up to 2000 m of younger subaerial alkali basaltic lavas unconformably overlying the submarine series. The plutonic suite (C) is overlain abruptly by more than 1800 m of sills (B), 0.4-1 m thick on average, with minor screens of lavas and breccias. Extrusives (A) form a 1750 m thick sequence of pillow lavas, breccias, and hyaloclastites. The clastic rocks increase in abundance upward and are of four main types: (1) breccias, consisting of partly broken pillows, formed nearly in situ, (2) heterolithologic pillow fragment breccias, (3) hyaloclastites composed dominantly of highly vesicular lapJill and ash sized shards, the latter thought •to have formed by near surface explosive eruptions and been subsequently transported downslope by mass flows, (2) and (3) being interpreted to have been resedimented, and (4) pillow scoria breccias from the upper 700 m of the extrusive section consisting of amoeboidal, highly vesicular "pillows" and lava stringers and local bombs, probably formed by cracking and "bleeding" of gas-rich expanding pillow lava and some shallow submarine/subaerial lava fountaining. The extrusive series is chemica!ly and mi•eralogically crudely zoned, with the most differentiated rocks (metatrachytes and mugearires) at the base and most picritic: lavas occurring near the top of the series. Subsequent to emplacement, the entire extrusive and intrusive series has been hydrothermally altered, the lower part to greenschist and the upper part to smectite--zeolite facies mineral assemblages. The La Palma succession, combined with evidence from surface studie s of seamounts, suggests that seamounts are formed by intrusive and extrusive processes in approximately equal portions. The nature of eruptive clasti c and depositional mechanisms changes drastically during growth of a seamount if the critical depth for major magmatic degassing is surpassed and especially if magmatic explosive processes can occur at very shallow water depth, the critical depth dependi'ng on magma and thus volatile composition. •Changes in slopes of a seamount influence depositional processes. Based on these factors, at least three major depositional sites develop as a seamount grows' summir, flank, and apron facies. Nonexplosive, extrusive processes prevail in the Deep Water Stage, dominant•!y producing pillow lavas (75%). These consist of individual pillow volcanoes'Up to 200 m high, with large pillows near the base and decreasing pillow size toward the top Of a volcano. Pillow breccias•, and pillow fragment breccias comprise approximately 20...