Basaltic tuyas are glaciovolcanoes that form when substantial focused eruptions take place beneath thick ice. None have been witnessed, so models reconstructing tuya formation are grounded in detailed fieldwork. A key feature of many basaltic tuyas is the presence of volcanic and volcaniclastic rocks that indicate the sustained presence of an encircling meltwater lake during the eruption.

Here we provide the first description of Þórólfsfell (Thórólfsfell), a basaltic tuya from Iceland, which is sufficiently distinct from previously described tuyas to be considered a new type of basaltic glaciovolcano.

Thórólfsfell is an asymmetric tuya with an area of c.8 km², base-to-top height of c.450 m, and volume of c.2.2 ± 0.4 km³ that has been emplaced onto the approximately 12^o sloping lower southern flanks of Tindfjallajökull central volcano.

Thórólfsfell shares only two major morphological characteristics with other basaltic tuyas: (1) a sub-horizontal top comprising subaerial lavas; (2) a clear vertical topographic expression, which reflects preferential upwards edifice growth due to lateral confinement by encircling ice and/or meltwater. There is no evidence for the presence of a large and long-lived syn-eruptive meltwater lake.

The Thórólfsfell eruption is effusion-dominated, and there is a gradual reduction in cooling fractures in lavas with elevation. The eruption is divided into three Stages. Stage I forms a c.110 m thick drape onto an irregular but persistently c.12^o dipping basement of older basaltic tuffs; Stage I consists of palaeoslope-parallel lava lobes with abundant cooling fractures, accompanied by abundant breccias. Stage II comprises a c.240 m thick stack of c.12^o dipping stacked lava lobes with abundant cooling fractures, and occasional autobreccias. Stage III is c.110 m thick, and whilst early lavas have cooling fractures, the final Stage III lavas are sub-horizontal, subaerial pahoehoe lava flows.

Our model for the formation of Thórólfsfell has two key features. The first is that the inclined basement has facilitated the downslope movement of meltwater away from the eruption site into an efficient gravity-assisted subglacial meltwater drainage system. The second is that there is a close connection between the vertical growth of the tuya and the ice above, with each successive lava in the growing stack being close to and/or in contact with the overlying ice. This repeated process provides the regular (but transient) meltwater supply necessary to produce a c.350 m stack of similarly-cooled lava carapaces.

From a hazards perspective, a Thórólfsfell-style eruption is of little concern as rapid and steady meltwater drainage away from the eruption site would prevent the high-magnitude glacial outburst floods that require accumulated meltwater. The Thórólfsfell eruption provides a new perspective on effective meltwater dispersal away from tuya-building eruptions on dipping palaeoslopes, and on lava-ice interactions during subglacial eruptions. The products of other subglacial eruptions onto dipping basements, producing Thórólfsfell-type tuyas, await study.

This first description of a new type of basaltic glaciovolcano may aid in the identification and interpretation of similar glaciovolcanoes on Earth and Mars that have yet to be discovered.

玄武岩状火山岩是冰川火山，是在浓厚的冰层下大量集中爆发时形成的。没有人目击过，因此重建突崖形成的模型是基于详细的野外工作。许多玄武岩风洞的一个主要特征是火山岩和火山碎屑岩的存在，表明火山喷发过程中环绕的融水湖持续存在。

在这里，我们提供Þórólfsfell（Thórólfsfell）的第一个描述，它是来自冰岛的玄武岩风云岩，与先前描述的风云岩有足够的区别，被认为是新型的玄武岩冰川火山。

Thórólfsfell是一个不对称的风铃，面积约8 km ²，底顶高度约450 m，体积c.2.2±0.4 km ³，已放置在大约12 ^o倾斜的南部下部侧面上Tindfjallajökull中央火山。

Thórólfsfell与其他玄武岩嘴类仅具有两个主要的形态特征：（1）包括地下熔岩的近水平顶；（2）清晰的垂直地形表达，反映了由于包围冰和/或融化水而引起的侧向封闭，导致优先的高层建筑生长。有一个大的和长期的存在，没有证据SYN -eruptive融水湖。

Thórólfsfell火山喷发以渗出为主，随着高度的升高，熔岩的冷却裂缝逐渐减少。喷发分为三个阶段。第一阶段在较老的玄武质凝灰岩的不规则但持续约12 ^o浸入地下室上形成约110 m厚的垂布；第一阶段由古​​坡平行的熔岩叶组成，具有丰富的冷却裂缝，并伴有大量角砾岩。第二阶段包括约240 m厚的c.12 ^o的烟囱，浸入堆积的熔岩裂片，具有丰富的冷却裂缝，偶有自角砾岩。第三阶段约为110 m厚，虽然早期熔岩具有冷却性裂缝，但第三阶段最终的熔岩为亚水平，地下的hoe草熔岩流。

我们的Thórólfsfell形成模型具有两个关键特征。首先是倾斜的地下室已经促进了融化水从喷发点的下坡运动，进入了有效的重力辅助冰川下融化水排放系统。第二个是在风口的垂直生长与上方的冰之间存在紧密的联系，在生长的烟囱中的每个相继的熔岩都靠近并/或与上覆的冰接触。这个重复的过程提供了产生约350 m堆类似冷却的熔岩甲壳所需的常规（但瞬变）熔体水供应。

从灾害的角度看，Thórólfsfell式喷发几乎没有问题，因为从喷发地点快速稳定地排出熔体水将阻止需要积累熔体水的高强度冰川爆发洪水。Thórólfsfell喷发提供了一个新的观点，可以有效地分散融水，使其远离浸没在古坡上的突崖建筑喷发，以及冰川下喷发期间熔岩与冰的相互作用。将其他冰期下爆发的产物沉积到浸入的地下室中，产生Thórólfsfell型金枪鱼，有待研究。

对新型玄武岩冰川火山的首次描述可能有助于鉴定和解释地球和火星上尚未发现的类似冰川火山。