**5.4 Ar40-Ar39 dating**

A sample by sample result is presented in **Table 5**. The Ar/Ar ages span between 1.3 and 2.5 Ma, confirm the earlier K-Ar ages of 2.1 and 1.9 0.31 Ma reported by [1] on dolerites on the Jos Plateau. The short interval in the radiometric ages suggests volcanic eruptions occurred at discrete times, separated by short periods of non-activity at a mean age average of 0.55 Ma (CN3 = 2.500 0.318 Ma and CN5 = 1.970 0.173 Ma). This long period must have been dominated by profound erosion. The considerable long-time difference from the oldest to the youngest eruption suggests that there was relatively steady magma source overtime.

**Figure 8.**

**Figure 9.**

**20**

*AB = subalkaline basalts, AB = alkaline basalts).*

*Forecasting Volcanic Eruptions*

*Plot of Log (Zr/TiO2) ratio versus SiO2 [12] of the volcanic rocks of Jos Plateau Volcanic province (Sub-*

*SiO2 versus Na2O+K2O classification diagram of basalts of the Jos Plateau volcanoes [13].*

*Log Zr (ppm) versus Log (Zr/Y) (ppm) diagram [14] volcanic rocks of the Jos Plateau Volcanic province.*

as increase in the concentrations of Cl from 2.5 to 5.6 mg/l; SO4 from <0.33 to

*Spidergraph plot of incompatible element compositions of basaltic rocks from the Plateau volcanoes normalized*

order Mg > Ca > K > Na (**Table 5**). The highest concentrations of Mg (30 to ≤40 mg/l), Ca (21–25 mg/l), K (15 mg/l) Na (8–11 mg/l) are observed during the dry season (January–April) while lowest concentrations of Mg (16–25 mg/l), Ca (10–15 mg/l), K (4–7 mg/l) in the rainy season (August–October). The intermittent change of color of the Lake from clear blue to brown has been attributed to

**Figure 14** presents the REE patterns from the Crater Lake normalized to Chondrites. The REE concentrations are impoverished relative to Chondrite values (<1 Chondrite). There are significant variations in the LREE (0.03–0.18 Chondrite for La) relative to HREE (Gd-Lu). An important characteristic of the spectra is the similarities between the LREE patterns indicating similar source. The slight enrichment in LREE must have been influenced by fluid percolation through

the host crustal materials (host granite basement) rich in these elements.

The major anion concentrations from the lake vary in concentrations in the order of -HCO3 > Cl > SO4. The highest concentration of in the LREE range from <0.5 to 5.5 mg/l and 0.0675 to 0.0321 mg/l, respectively, and were observed during

*5.5.3 Anion concentrations (SO4, Cl, HCO3, NO3, F, Br, and PO4)*

In general, the major element concentrations in the Pidong Lake decrease in the

1.05 mg/l (**Table 5**).

**Figure 13.**

*to OIB [15].*

**23**

*5.5.1 Major element concentration/distribution*

*Is a Volcanic Eruption Possible in Nigeria? DOI: http://dx.doi.org/10.5772/intechopen.84253*

the increase in Fe concentrations into the Lake.

*5.5.2 Rare earth element (REEs) concentrations*

**Figure 12.**

*Ternary diagram of Ti/100 – Zr – Y\*3 [12] for the volcanic rocks of the Jos Plateau Volcanic province. WPB = D, within plate basalts; OFB = B, ocean flood basalts; LKT = A,B low potassium tholeiitic basalts; and CAB = D,C, calc-alkaline basalts.*

#### **5.5 Hydrogeochemistry of the Pidong Crater Lake**

Comparative hydrogeochemical parameters of previous study [7] and this present study is presented in **Table 5**. It shows clearly that pH and alkalinity have decreased overtime from 9.35 to ≥7.0 and from 335 to 145 mg/l, respectively as well

**Figure 13.**

*Spidergraph plot of incompatible element compositions of basaltic rocks from the Plateau volcanoes normalized to OIB [15].*

as increase in the concentrations of Cl from 2.5 to 5.6 mg/l; SO4 from <0.33 to 1.05 mg/l (**Table 5**).
